Tutorial 2

AS/NZS 3007:2013

AS/NZS 3007:2013

Australian/New Zealand Standard™

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Electrical equipment in mines and quarries—Surface installations and associated processing plant

AS/NZS 3007:2013 This Joint Australian/New Zealand Standard was prepared by Joint Technical Committee EL-023, Electrical Equipment for Mines and Quarries. It was approved on behalf of the Council of Standards Australia on 29 April 2013 and on behalf of the Council of Standards New Zealand on 23 April 2013.

This Standard was published on 24 June 2013.

The following are represented on Committee EL-023:

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Australian Cablemakers Association Australian Chamber of Commerce and Industry Australian Coal Association Australian Industry Group Aviation and Marine Engineers Association Consult Australia Department of Mines and Petroleum, WA Department of Natural Resources and Mines, Qld Mining Electrical and Mining Mechanical Engineering Society Ministry of Business, Innovation and Employment, New Zealand National Association of Testing Authorities Australia NSW Department of Trade and Investment, Regional Infrastructure and Services University of Newcastle WorkCover New South Wales

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This Standard was issued in draft form for comment as DR AS/NZS 3007.

AS/NZS 3007:2013

Australian/New Zealand Standard™

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Electrical equipment in mines and quarries—Surface installations and associated processing plant

Originated in Australia as AS 3007.1—1982, AS 3007.2—1982, AS 3007.3—1982, AS 3007.4—1985 and AS 3007.5—1987.

Previous editions AS 3007.1—2004, AS 3007.2—2004, AS 3007.3—2004, AS 3007.4—2004 and AS 3007.5—2004.

Jointly revised, amalgamated and redesignated AS/NZS 3007:2013.

COPYRIGHT © Standards Australia Limited/Standards New Zealand All rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher, unless otherwise permitted under the Copyright Act 1968 (Australia) or the Copyright Act 1994 (New Zealand).

Jointly published by SAI Global Limited under licence from Standards Australia Limited, GPO Box 476, Sydney, NSW 2001 and by Standards New Zealand, Private Bag 2439, Wellington 6140.

ISBN 978 1 74342 516 9

AS/NZS 3007:2013

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PREFACE This Standard was prepared by the Joint Standards Australia/Standards New Zealand Committee EL-023, Electrical Equipment for Mines and Quarries, to supersede Parts 1 to 5 of AS 3007—2004.

The objective of this Standard is to set out guiding principles for the design, installation, and operation of electrical equipment in mines and quarries so as to ensure the safety of persons, livestock and property, and the proper functioning of the plant.

Australian mining operations typically involve most aspects of electrical engineering, ranging from such areas as high voltage transmission to the control of undesirable static electricity. A substantial number of Standards therefore apply to such work. This Standard consolidates these requirements together into the one document.

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This edition of the Standard differs from the previous editions in the following significant ways: (a)

This Standard incorporates the requirements for the surface of underground mines in addition to surface mines, quarries and associated processing plant.

(b)

Where issues are adequately covered by AS/NZS 3000, AS 2067, and AS 60204, they have been removed from this version of AS/NZS 3007 to prevent conflict.

(c)

Relevant parts of AS/NZS 4871 (series) that apply to installations covered by the scope of this Standard have been included.

(d)

Particular requirements have been included to address known deficiencies in installation and practices.

(e)

Definitions have been aligned with other key Standards.

(f)

Requirements for transportable/relocatable distribution and control equipment have been added.

(g)

The requirements for flexible feeder, trailing, and reeling cables have been expanded.

(h)

The requirements for overhead lines have been expanded.

(i)

The requirements for specific types of power supplies have been updated.

(j)

Requirements for labelling have been updated.

(k)

Requirements for managing change within the mining operation have been added.

(l)

Information about the power supply to safety critical infrastructure for underground mines has been added.

(m)

Requirements for reclaim and transfer tunnels have been added.

(n)

Information about variable speed drives has been added.

(o)

Appendix F has been added to provide earthing requirements for mines. (This Appendix will be deleted by amendment when AS 2067 has been amended to include mine earthing.)

In recognition of changes introduced in this revision of this Standard, existing installations and equipment should be reviewed against the requirements of this Standard.

Descriptions of TN, TT and IT power supply systems have been retained as they are not found elsewhere within standards.

The terms ‘normative’ and ‘informative’ are used to define the application of the appendix to which they apply. A normative appendix is an integral part of a standard, whereas an informative appendix is only for information and guidance.

Statements expressed in mandatory terms in notes to tables are deemed to be requirements of this Standard.

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AS/NZS 3007:2013

CONTENTS Page SECTION 1 SCOPE AND GENERAL 1.1 SCOPE ......................................................................................................................... 7 1.2 REFERENCED DOCUMENTS ................................................................................... 8 1.3 DEFINITIONS........................................................................................................... 11

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SECTION 2 GENERAL REQUIREMENTS 2.1 RISK MANAGEMENT ............................................................................................. 18 2.2 LOW VOLTAGE AND EXTRA LOW VOLTAGE INSTALLATIONS ................... 18 2.3 HIGH VOLTAGE INSTALLATIONS ...................................................................... 18 2.4 EARTHING ............................................................................................................... 18 2.5 REMOVAL OF POWER AT A CLOSED ELECTRICAL OPERATING AREA ...... 19 2.6 ELECTRICAL MACHINERY................................................................................... 19 2.7 PROTECTION FROM NON-ELECTRICAL HAZARDS ......................................... 19 2.8 PROTECTION FROM ELECTRICAL HAZARDS ................................................... 19 2.9 ISOLATING SWITCHES (DISCONNECTORS) ...................................................... 20 2.10 CIRCUIT-BREAKERS .............................................................................................. 21 2.11 CABLES .................................................................................................................... 21 2.12 SYSTEM DESIGN .................................................................................................... 21 2.13 GENERAL REQUIREMENTS FOR ELECTRICAL COMPONENTS ..................... 22 SECTION 3 PROTECTION AGAINST OVERLOADS AND FAULTS 3.1 INTRODUCTION ..................................................................................................... 25 3.2 GENERAL RULE...................................................................................................... 25 3.3 AUTOMATIC INTERRUPTION—PROTECTION AGAINST OVERCURRENT DUE TO OVERLOAD .............................................................................................. 25 3.4 COORDINATION OF OVERLOAD AND SHORT-CIRCUIT PROTECTION AFFORDED BY SEPARATE DEVICES .................................................................. 26 3.5 EARTH FAULT PROTECTION ON IMPEDANCE EARTHED IT SYSTEMS ....... 26 SECTION 4 ELECTRICAL WIRING OF EQUIPMENT AND MACHINERY 4.1 GENERAL ................................................................................................................. 28 4.2 ELECTRICAL ISOLATION ..................................................................................... 28 4.3 ISOLATING FOR MECHANICAL MAINTENANCE ............................................. 28 4.4 REMOTE CONTROL................................................................................................ 28 4.5 PENDANT CONTROL (UMBILICAL CORD) ........................................................ 28 4.6 CABLING ................................................................................................................. 29 4.7 ROTATING ELECTRICAL MACHINES ................................................................. 29 4.8 MOBILE MACHINERY CABLE ATTACHMENTS ................................................ 30 4.9 CABLE REELS ......................................................................................................... 30 4.10 MOBILE MACHINERY LIGHTING SYSTEMS ..................................................... 31 4.11 CONTROL CIRCUITS AND CONTROL DEVICES ................................................ 31 SECTION 5 TRANSPORTABLE/ RELOCATABLE DISTRIBUTION AND CONTROL EQUIPMENT 5.1 GENERAL ................................................................................................................ 34 5.2 TRANSPORTABLE SUBSTATIONS ....................................................................... 35 5.3 DISTRIBUTION AND CONTROL EQUIPMENT.................................................... 38 5.4 FLEXIBLE CABLE TERMINATION BOXES ......................................................... 38

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SECTION 6 FLEXIBLE FEEDER, TRAILING AND REELING CABLE SELECTION, APPLICATION AND USE 6.1 DESIGN OF CABLES ............................................................................................... 39 6.2 POWER CABLE TWIST LIMITATION ................................................................... 40 6.3 CABLE CONNECTORS ........................................................................................... 41 6.4 MOVING CABLES ................................................................................................... 41 6.5 INSTALLATION OF CABLES ................................................................................. 43 6.6 CABLE REPAIR ....................................................................................................... 48 6.7 PRECAUTIONS DURING LIGHTNING STORMS ................................................. 48 SECTION 7 OVERHEAD LINES 7.1 GENERAL ................................................................................................................. 49 7.2 EASEMENTS ............................................................................................................ 49 7.3 MINE OWNED/OPERATED OHLS ......................................................................... 50 7.4 OHL CORRIDORS AND WORK NEAR OHLS ....................................................... 51 7.5 CLEARANCE TO MOBILE PLANT ........................................................................ 53 7.6 CLEARANCES TO HAND-HELD OBJECTS .......................................................... 55 7.7 CLEARANCE TO EXCAVATIONS ......................................................................... 55 7.8 CLEARANCE TO BLASTING OPERATIONS ........................................................ 55 7.9 CLEARANCE TO STOCKPILE AND TAILING AREAS ........................................ 56 7.10 CLEARANCE TO STORAGE AREAS ..................................................................... 56 7.11 CLEARANCE TO STRUCTURES AND PEOPLE TRANSIT AREAS .................... 56 7.12 REDUCTION OF CLEARANCES ............................................................................ 56 7.13 MOVING OF OHLS .................................................................................................. 56 7.14 PRECAUTIONS DURING LIGHTNING STORMS ................................................. 57 7.15 OPERATIONS INVOLVING LONG METALLIC STRUCTURES .......................... 57 7.16 CLEARING VEGETATION NEAR OHLS ............................................................... 57 7.17 MINE SITE INFORMATION ON OHLS .................................................................. 57 7.18 EMERGENCY RESPONSE PLAN FOR CONTACT WITH OHLS ......................... 57 7.19 EMERGENCY ACTION IF THERE IS AN ACCIDENT ......................................... 58 SECTION 8 SPECIFIC POWER SUPPLIES 8.1 POWER SUPPLIES FROM MOBILE MACHINERY .............................................. 59 8.2 SELF-CONTAINED POWER SYSTEMS ................................................................. 59 8.3 WELDING MACHINES AND EQUIPMENT ........................................................... 59 8.4 INVERTERS AND UNINTERRUPTABLE POWER SUPPLIES ............................. 59 8.5 RELOCATABLE BUILDINGS AND IT EARTHING SYSTEMS ............................ 60 SECTION 9 ELECTRICITY SUPPLY TO SAFETY CRITICAL MINE INFRASTRUCTURE FOR UNDERGROUND MINES 9.1 SAFETY CRITICAL ELECTRICAL SYSTEMS ...................................................... 61 9.2 CONTINUITY OF THE ELECTRICAL SUPPLY TO THE MINE ........................... 62 9.3 CONTINUITY OF SUPPLY TO THE UNDERGROUND WORKINGS CONTAINING SAFETY CRITICAL INFRASTRUCTURE ..................................... 62 9.4 CONTINUITY OF SAFETY CRITICAL, ELECTRICALLY POWERED VENTILATION EQUIPMENT ................................................................................. 64 9.5 MONITORING AND CONTROL ............................................................................. 65 9.6 POWERED WINDING SYSTEMS ........................................................................... 66 9.7 POWER SUPPLIES TO DE-WATERING AND FIREDAMP DRAINAGE PLANT AND EQUIPMENT ................................................................................................... 67

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SECTION 10 TRANSPORT CONVEYOR SYSTEMS 10.1 GENERAL ................................................................................................................. 68 10.2 CONVEYOR CONTROLLERS ................................................................................ 68 10.3 CABLES OF MOVEABLE CONVEYORS ............................................................... 69 10.4 BELT SPLICING EQUIPMENT ............................................................................... 69 SECTION 11 DEEP-WELL TYPE PUMPS AT SURFACE MINING OPERATIONS 11.1 GENERAL ................................................................................................................. 70 11.2 RISERS AS PROTECTIVE CONDUCTORS ............................................................ 70 11.3 CONTINUED OPERATION AFTER FIRST EARTH FAULT ................................. 70 11.4 EQUIPOTENTIAL BONDING ................................................................................. 70 11.5 EXEMPTION FROM INSULATION-MONITORING DEVICE .............................. 71 11.6 DOUBLE LINE TO EARTH FAULTS ..................................................................... 71 SECTION 12 RECLAIM AND TRANSFER TUNNELS FOR COAL MINES 12.1 GENERAL ................................................................................................................. 72 12.2 AUTOMATIC GAS MONITORING SYSTEM......................................................... 72

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SECTION 13 FIRE DETECTION AND PROTECTION SYSTEMS FOR ELECTRICAL AREAS 13.1 GENERAL ................................................................................................................. 74 13.2 GENERAL PROTECTION REQUIREMENTS......................................................... 74 13.3 ADDITIONAL REQUIREMENTS AND RECOMMENDATIONS .......................... 76 SECTION 14 STATIC ELECTRICITY, RADIOACTIVE SOURCES AND INDUCTIVE SOURCES 14.1 STATIC ELECTRICITY ........................................................................................... 77 14.2 ELECTROSTATIC PRECIPITATORS ..................................................................... 77 14.3 RADIOACTIVE SOURCES ...................................................................................... 77 14.4 HAZARDS FROM INDUCTION .............................................................................. 77 SECTION 15 LABELS, SIGNAGE AND INFORMATION REQUIREMENTS AND COLOUR CODING OF ENCLOSURES 15.1 GENERAL ................................................................................................................ 78 15.2 SPECIFIC REQUIREMENTS ................................................................................... 78 15.3 ENCLOSURES WITH COVERS GUARDING ACCESS TO LIVE CONDUCTORS ................................................................................................................................... 79 15.4 VOLTAGE IDENTIFICATION OF ELECTRICAL ENCLOSURES ........................ 79 SECTION 16 OPERATIONAL REQUIREMENTS 16.1 GENERAL ................................................................................................................. 80 16.2 RESTRICTIONS ON ACCESS BY PERSONNEL ................................................... 80 16.3 OPERATIONS INVOLVING PERSONNEL WORKING IN THE VICINITY OF EXPOSED LIVE PARTS .......................................................................................... 80 16.4 USE OF RADIO REMOTE CONTROL EQUIPMENT ............................................. 81 16.5 OVERHEAD LINES ................................................................................................. 81 SECTION 17 MANAGEMENT OF ALTERATIONS TO THE MINING OPERATION 17.1 GENERAL ................................................................................................................ 82 17.2 MANAGEMENT OF CHANGE ................................................................................ 82

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APPENDICES A TN, TT AND IT SYSTEMS DESCRIPTION ............................................................ 84 B PROTECTIVE DEVICES AND THEIR USES ......................................................... 92 C GUIDELINES FOR LOW SIGNAL LEVEL SYSTEMS AND COMMUNICATION SYSTEMS ............................................................................ 102 D VARIABLE SPEED DRIVES ................................................................................. 107 E DOCUMENTATION ............................................................................................... 110 F EARTHING ............................................................................................................. 112

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STANDARDS AUSTRALIA/STANDARDS NEW ZEALAND Australian/New Zealand Standard Electrical equipment in mines and quarries—Surface installations and associated processing plant

S E C T I O N

1

S C O P E

A N D

G E N E R A L

1.1 SCOPE This Standard applies to the design, installation and operation of electrical plant and equipment installed at surface mining and quarrying operations, the surface of underground mines, and associated processing plants.

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There are particular requirements for the following: (a)

The operation of equipment and personnel interacting with electrical installations.

(b)

Trailing cable fed machinery used for digging/winning product (i.e. electric draglines, electric face shovels, floating dredges, and electric drills), and transporting, stacking and reclaiming product (i.e. conveying systems, balance machinery such as stackers and reclaimers).

(c)

Power generation and distribution equipment used to supply trailing cables and relocatable plant.

(d)

Power and distribution on IT (impedance earthed) systems, TN and TT systems.

(e)

Earthing systems for power distribution to underground mines.

(f)

Overhead lines on a mine site.

(g)

Relocatable plant and buildings.

(h)

Fixed plant.

This Standard does not apply to the following areas: (i)

Earth moving machinery covered by ISO 6165 and not fed by trailing or reeling cables.

(ii)

The design of mine winder control systems.

The Standard describes the types of electrical distribution systems.

This Standard supplements the requirements of AS/NZS 3000, AS 2067, and AS 60204 for installations in the harsh environments found in mining and quarrying operations.

Where equipment is located on the surface and there is conflict with the AS/NZS 4871 series, this Standard takes precedence.

NOTES: 1 The requirements of this Standard may be read in conjunction with, but do not take precedence over, regulations of a regulatory authority that may apply in a specific area.

2 In some instances, State legislation refers to parts of the previous version of this Standard, therefore it is important to note that these parts have now been combined into the one document.

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1.2 REFERENCED DOCUMENTS The following documents are referenced in this Standard:

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AS 1318

Use of colour for the marking of physical hazards and the identification of certain equipment in industry (known as the Industrial Safety Colour Code)

1319

Safety signs for the occupational environment

1603

Automatic fire detection and alarm systems (series)

1670

Fire detection, warning, control and intercom systems—System design, installation and commissioning (series)

1674 1674.2

Safety in welding and allied processes—Electrical Part 2: Electrical

1755

Conveyors—Safety requirements

1824

Insulation co-ordination (series)

1851

Routine service of fire protection systems and equipment

2067

Substations and high voltage installations exceeding 1 kV a.c.

2118

Automatic fire sprinkler systems (series)

2187 2187.2

Explosives—Storage, transport and use Part 2: Use of explosives

2290 2290.3

Electrical equipment for coal mines—Maintenance and overhaul Part 3: Maintenance of gas detecting and monitoring equipment

2293 2293.1

Emergency escape lighting and exit signs for buildings Part 1: System design, installation and operation

2444

Portable fire extinguishers and fire blankets—Selection and location

2467

Maintenance of electrical switchgear

2665

Smoke/heat venting systems—Design, installation and commissioning

2700

Colour standards for general purposes

4024

Safety of machinery (series)

4436

Guide for the selection of insulators in respect of polluted conditions

4777

Grid connection of energy systems via inverters (series)

7240

Fire detection and alarm systems (series)

60044

Instrument transformers (series)

60076 60076.1

Power transformers Part 1: General (IEC 60076-1, Ed. 2.1 (2000) MOD)

60204 60204.1 60204.11

Safety of machinery—Electrical equipment of machines Part 1: General requirements (IEC 60204-1, Ed. 5 (FDIS) MOD) Part 11: Requirements for HV equipment for voltages above 1000 V a.c. or 1500 V d.c. and not exceeding 36 kV (IEC 60204-11, Ed. 1.0 (2000) MOD)

60529

Degrees of protection provided by enclosures (IP Code)

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AS 60974 60974.1 60974.6 61508

Arc welding equipment Part 1: Welding power sources (IEC 60974-1:2000, MOD) Part 6: Limited duty portable arc welding and allied process power sources (IEC 60974-6:2003, MOD) Functional safety of electrical/electronic/programmable electronic safetyrelated systems (series)

61800 61800.3

Adjustable speed electrical power drive systems Part 3: EMC requirements and specific test methods

62061

Safety of machinery—Functional safety of safety-related electrical, electronic and programmable electronic control systems

AS/NZS 1020

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AS/NZS 3007:2013

The control of undesirable static electricity

1299

Electrical equipment for mines and quarries—Explosion-protected three-phase restrained plugs and receptacles for working voltages up to and including 3.3 kV

1668 1668.1

The use of ventilation and airconditioning in buildings Part 1: Fire and smoke control in multi-compartment buildings

1747

Reeling, trailing and feeder cables used for mining—Repair, testing and fitting of accessories

1768

Lightning protection

1850

Portable fire extinguishers—Classification, rating and performance testing

2081

Electrical protection devices for mines and quarries

2802

Electric cables—Reeling and trailing—For mining and general use (other than underground coal mining)

3000

Electrical installations (known as the Australian/New Zealand Wiring Rules)

3001

Electrical installations—Transportable structures and vehicles including their site supplies

3008 3008.1.1

Electrical installations—Selection of cables Part 1.1: Cables for alternating voltages up to and including 0.6/1 kV—Typical Australian installation conditions

3010

Electrical installations—Generating sets

3012

Electrical installations—Construction and demolition sites

3100

Approval and test specification—General requirements for electrical equipment

3439 3439.1

Low-voltage switchgear and controlgear assemblies Part 1: Type-tested and partially type-tested assemblies

3800

Electrical equipment for explosive atmospheres—Repair and overhaul

4240

Remote control systems for mining equipment (series)

4763

Safety of portable inverters

4836

Safe working on or near low-voltage electrical installations and equipment

4853

Electrical hazards on metallic pipelines

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AS/NZS 4871 4871.1 4871.2 4871.3

Electrical equipment for mines and quarries Part 1: General requirements Part 2: Distribution, control and auxiliary equipment Part 3: Substations

5603

Stand-alone inverters—Performance requirements

7000

Overhead line design—Detailed procedures

60079 Explosive atmospheres 60079.10.1 Part 10.1: Classification of areas—Explosive gas atmospheres (IEC 60079-101, Ed. 1.0 (2008) MOD) 60079.10.2 Part 10.2: Classification of areas—Combustible dust atmospheres 60079.14 Part 14: Electrical installations design, selection and erection (IEC 60079-14, Ed 4.0 (2007) MOD) 60079.17 Part 17: Electrical installations inspection and maintenance 60079.29.2 Part 29.2: Gas detectors—Selection, installation, use and maintenance of detectors for flammable gases and oxygen 61000

Electromagnetic compatibility (EMC) (series)

62040

Uninterruptible power systems (UPS) (series)

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AS IEC 61511 AS ISO 14520 14520.1

Functional safety—Safety instrumented systems for the process industry sector (series) Gaseous fire-extinguishing systems—Physical properties and system design Part 1: General requirements (ISO 14520-1:2006, MOD)

AS/NZS AS/NZS ISO 31000 Risk management—Principles and guidelines IEC 61800 Adjustable speed electrical power drive systems 61800-5-1 Part 5-1: Safety requirements—Electrical, thermal and energy 61800-5-2 Part 5-2: Safety requirements—Functional 60255

Measuring relays and protection equipment (series)

60353

Line traps for a.c. power systems

60481

Coupling devices for power line carrier systems

60495

Single sideband power-line carrier terminals

60751

Industrial platinum resistance thermometers and platinum temperature sensors

IEC/TR 60663

Planning of (single-sideband) power line carrier systems

ISO 6165 13849 13849-1

Earth-moving machinery—Basic types—Identification and terms and definitions Safety of machinery—Safety-related parts of control systems Part 1: General principles for design

16732 16732-1

Fire safety engineering—Fire risk assessment Part 1: General

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BS 6657

AS/NZS 3007:2013

Assessment of inadvertent initiation of bridge wire electro-explosive devices by radio-frequency radiation. Guide

ENA Guides Doc 023 ENA guidelines for safe vegetation management works near overhead lines EG0

A risk based approach to earthing

IEEE 80

Guide for Safety in Ac Substation Grounding

1584

Guide for performing arc-flash hazard calculations

NFPA 70E

Electrical safety in the workplace

ANSI/IEEE C37.2 Electrical power system device function numbers, acronyms and contact designations ARPANSA Code of practice and safety guide for radiation protection and radioactive waste management in mining and mineral processing, 2005.

1.3 DEFINITIONS For the purpose of this Standard the following definitions shall apply:

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1.3.1 Armour (of a cable) A covering consisting of metal tapes or wires used to protect the cable from external mechanical effects.

1.3.2 Closed electrical operating area An area dedicated for the operation of electrical installations and equipment to which access is intended to be restricted to skilled or instructed persons or to lay personnel under the direct supervision of skilled or instructed persons.

NOTES: 1 Examples of such locations include substations, enclosed switchgear and distribution installations, transformer enclosures, enclosed switchgear bays or cubicles, distribution installations in sheet metal housings or in other closed installations.

2 Typically access to closed areas is only by the use of a key or tool to open a door or remove a protective barrier, and where that access is clearly marked by appropriate warning signs.

1.3.3 Dead-man control A control switch (or other similar device), either hand or foot operated, which upon release automatically returns to the off position and causes the machinery to be brought safely to rest.

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1.3.4 Direct contact Contact with a conductor or conductive part that is live in normal service.

1 2 3 N Busb ar s Is

Is: touch current

FIGURE 1.1 DIRECT CONTACT

1.3.5 Direct supervision Direct supervision is where a person is under the immediate control and direction of the supervisor of electrical work who will be in attendance at all times.

1.3.6 Earth electrode Conductive part which may be embedded in the soil or in a specific conductive medium, (e.g. concrete or coke) in electric contact with the earth.

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1.3.7 Earth fault current A current which flows from phase conductors to earth, protective conductors or protective enclosures, etc., from the point of insulation breakdown.

[IEV 826-13-05] 1.3.8 Earthable point The point in the power system (e.g. of the transformer or generator) which would be connected to earth if the system were to be earthed.

NOTE: The earthable point may be the neutral point depending on the type of power system.

1.3.9 Electrical equipment Item used for such purposes as generation, conversion, transmission, distribution or utilization of electric energy, such as electric machines, transformers, switchgear and controlgear, measuring instruments, protective devices, wiring systems, current-using equipment.

[IEV 26-16-01] 1.3.10 Electrical installation Electrical equipment installed for the purposes of conveyance, control, measurement or use of electricity, where electricity is or is to be supplied for consumption; includes electrical equipment supplied from a distributor’s system or a private generating system.

NOTES: 1 An electrical installation usually commences at the point of supply and finishes at a point (in wiring) but does not include low voltage equipment connected by flexible cable or cord.

2 Unless the context otherwise dictates, the term ‘installation’ is used in this Standard to mean electrical installation.

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AS/NZS 3007:2013

1.3.11 Enclosure A part providing an appropriate degree of protection of equipment against external influences and against contact with live parts.

1.3.12 Equipotential bonding Provision of electric connections between conductive parts, intended to achieve equipotentiality.

[IEV 826-13-1] 1.3.13 Equipotential bonding conductor A protective conductor for ensuring equipotential bonding.

1.3.14 Exposed conductive part A conductive part of electrical equipment that— (a)

can be touched with the standard test finger as specified in AS/NZS 3100; and

(b)

is not a live part but can become live if basic insulation fails.

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EXCEPTION: The term ‘exposed conductive part’ does not apply to the following: (i)

Conductive parts within an enclosure where the parts cannot be touched unless a key or a tool is required to remove the covers of the enclosure.

(ii)

Conductive parts within electrical equipment where the parts cannot be touched in normal use and movement of the electrical equipment, because of its configuration and size.

(iii) Conductive parts that are effectively and permanently separated from live parts by— (A)

double insulation; or

(B)

other conductive parts that are earthed.

(iv)

Conductive parts that are in the form of nameplates, screw heads, covers and similar attachments that cannot become live in the event of failure of insulation of live parts because of the manner in which they are supported and fixed.

(v)

A removable or hinged conductive panel fitted to a switchboard or other enclosure containing conductors that are so located and/or restrained that, in the event of any conductor becoming detached from a terminal or mounting, the conductor is incapable of making contact with the panel.

1.3.15 Extraneous conductive part A conductive part that does not form part of an electrical installation but that may be at the electrical potential of a local earth.

NOTE: Examples of extraneous conductive parts include the following: (a) Metal waste, water or gas pipe from outside. (b) Cooling or heating system parts. (c) Metal or reinforced concrete building components. (d) Steel-framed structure. (e) Floors and walls of reinforced concrete without further surface treatment. (f) Tiled surfaces, conductive wall coverings. (g) Conductive fittings in washrooms, bathrooms, lavatories, toilets, etc. (h) Metallized papers.

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1.3.16 Fault current A current resulting from an insulation failure or the bridging of insulation.

1.3.17 Flexible feeder cable An insulated cable that may be moved from time to time according to the operation without necessarily following the movements of the machinery.

1.3.18 Highest voltage (of a three-phase system) The highest r.m.s. phase-to-phase voltage which occurs under normal operating conditions at any time and at any point of the system, excluding voltage transients (such as those due to system switching) and temporary voltage variations due to abnormal conditions (such as those due to fault conditions or the sudden disconnection of large loads).

1.3.19 Indirect contact Contact with a conductive part that is not normally live but has become live under fault conditions (because of insulation failure or some other cause).

Insulation f ailure 1 2 3 Id

E ar thing conduc tor

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Is

Is: touch current I d: f ault current

FIGURE 1.2 INDIRECT CONTACT

1.3.20 Instructed person Person adequately advised or supervised by a skilled person to enable them to avoid dangers which electricity may create.

1.3.21 Insulation-monitoring device A device which causes a signal to be given in the event of reduced insulation resistance to earth.

1.3.22 IT system A power system having the earthable point not connected to earth, or connected to earth through impedance (resistor or reactor), the exposed conductive parts of the installation being connected to earth electrodes which may be the same as those used for the earthing resistor or reactor.

NOTE: For a description of the system, see Appendix A.

1.3.23 Leakage current (in an installation) A current which, in the absence of a fault, flows to earth or to extraneous conductive parts in a circuit, and which may have a capacitive component including that resulting from the deliberate use of capacitors.

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1.3.24 Lightning protection earth (LPE) That part of a lightning protection system (LPS) intended to discharge lightning currents into the general mass of the earth.

1.3.25 Live part A conductor or conductive part intended to be energized in normal use, including a neutral conductor.

NOTE: This term does not necessarily imply a risk of electric shock.

1.3.26 Machinery 1

Assembly of linked parts or components, at least one of which moves, with the appropriate machine actuators, control and power circuits, joined together for a specific application, in particular for the processing, treatment, moving or packaging of a material.

2

Assembly of machines which, in order to achieve the same end, are arranged and controlled so that they function as an integral whole.

1.3.27 Main earthing terminal A terminal or bar provided for the connection of protective conductors, including equipotential bonding conductors and conductors for functional earthing if any, to the means of earthing.

1.3.28 Mobile machinery

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Machinery which is capable of being readily moved about whilst it is in operation, e.g. flexible conveyors, electric face shovels, draglines, and overburden drills.

1.3.29 Mine underground earth (MUE) This is the power system earth for the underground electricity distribution whether into mine workings or ancillary boreholes.

1.3.30 Network earth (NE) Network operators earth by virtue of connection of their overhead earth wire or cable screens or simply being the earth system that their fault level will impact.

1.3.31 Neutral conductor (symbol N) The conductor of a three-wire or multi-wire system that is maintained at an intermediate and approximately uniform potential in respect of the active or outer conductors, or the conductor of a two-wire system that is connected to earth at its origin.

1.3.32 Nominal voltage (of a three-phase system) The r.m.s. phase-to-phase voltage by which the system is designated and to which certain operating characteristics of the system are related.

1.3.33 Overhead line (OHL) An electric line, having bare or insulated conductors, supported to maintain a specified minimum distance above ground level.

1.3.34 Prospective touch voltage Voltage between simultaneously accessible conductive parts when those conductive parts are not being touched by a person or an animal.

[IEV 826-11-03]

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1.3.35 Protective barrier (electrically) A part providing protection against direct contact from any usual direction of access.

[IEV 826-12-02] 1.3.36 Protective conductor (symbol PE) A conductor required by some measures for protection against electric shock for electrically connecting any of the following parts: (a)

Exposed conductive parts.

(b)

Extraneous conductive parts.

(c)

Main earthing terminal (see Clause 1.3.27).

(d)

Earth electrode.

(e)

Earthed point of the source or artificial neutral.

NOTE: This is equivalent to protective earth conductor as defined in AS/NZS 3000.

1.3.37 Quarry An open-air site for the extraction and processing of materials such as limestone, gravel, clay, etc.

NOTE: Any reference within this Standard to a mine or mining, also means quarry or quarrying.

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1.3.38 Reeling and trailing cables Cables having flexible conductors, insulation incorporating conductor and insulation screens where appropriate, filling, reinforcement where appropriate, one or more protective coverings, and being specially designed to provide flexible electrical connections between portable or mobile machinery and a point of supply.

1.3.39 Relocatable plant Plant which is designed to be relocated from time to time during mining activities.

1.3.40 Residual current Algebraic sum of the values of the electric currents in all live conductors, at the same time at a given point of an electric circuit in an electrical installation.

[IEV 826-11-1] 1.3.41 Restrained plug and receptacle A restrained plug and receptacle is a device where the individual receiving sockets within the plug are arranged to have accessible pins. The plug is retained in the receptacle by a fixing device that can be operated without the use of a tool.

NOTE: For typical arrangements used in coal mining, see AS/NZS 1299.

1.3.42 Shall Indicates that a statement is mandatory.

1.3.43 Should Indicates a recommendation.

1.3.44 Skilled persons Persons with technical knowledge or sufficient experience to enable them to avoid dangers which electricity may create.

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1.3.45 TN system A power system having the earthable point directly connected to earth and the exposed conductive parts of the installation being connected by protective conductors to the earthable point of the power system.

NOTE: For information on TN systems, see Appendix A.

1.3.46 Touch voltage Voltage appearing between simultaneously accessible parts.

NOTES: 1 This term is used only in connection with fault protection.

2 In certain cases the value of the touch voltage may be appreciably influenced by the impedance of the person or livestock in contact with these parts.

1.3.47 TT system A power system having the earthable point directly connected to earth, the exposed conductive parts of the installation being connected to earth electrodes which are electrically independent of the earth electrodes of the power system.

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NOTE: For information on TT systems, see Appendix A.

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2

G E N E R A L

R E Q U I R E M E N T S

NOTE: Specific requirements are given in Sections 3 to 17.

2.1 RISK MANAGEMENT Risk management techniques shall be employed for the purposes of identification and assessment of risks associated with the use of electricity. This includes the identification of controls, and the implementation, validation and monitoring of those controls during the full life cycle, including the design, manufacture, commissioning, operation, maintenance and decommissioning of the equipment.

NOTE: Techniques may include hazard analysis, risk assessment, failure mode and effect analysis, and functional safety analysis.

Control measures shall be implemented, as appropriate, to account for all foreseeable hazards.

Reference should be made to AS/NZS ISO 31000, AS 60204.1, AS 62061, ISO 13849-1, AS 4024 (series) and AS/NZS 4240 (series).

For simple tasks, job safety analysis (JSA) or other site-specific procedures may be appropriate.

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NOTE: The use of programmable electronic systems introduces an additional possibility of failure or defect if access to safety related software is not properly designed and monitored.

2.2 LOW VOLTAGE AND EXTRA LOW VOLTAGE INSTALLATIONS Low voltage and extra low voltage electrical installations shall comply with the requirements of AS/NZS 3000.

2.3 HIGH VOLTAGE INSTALLATIONS High voltage electrical installations shall comply with the requirements of AS/NZS 3000, AS 2067 and AS/NZS 7000.

2.4 EARTHING Touch voltage clearance times shall be in accordance with AS/NZS 3000 and AS 2067 and Tables F2 and F3, Appendix F, as applicable.

Earthing for electrical supplies into underground mines and to flexible cable-fed plant shall be in accordance with Appendix F. These are supplementary to the requirements of AS 2067, AS/NZS 3000, AS 60204.1 and AS 60204.11.

NOTE: Appendix F has been added to this edition to provide detailed earthing requirements.

Appendix F will be deleted by amendment when AS 2067 has been revised to address these issues.

The bond from the earthable point of the power system, if earthed, to the earthing system, is a highly critical connection. Performance, security, robustness, contingency, and proximity to the respective transformer are integral to the design.

The earthable point of a generator shall comply with AS/NZS 3010.

Equipotential bonding should be installed between metallic structures and plant that may be insulated from the structure (plant with rubber resilient mountings such as screens in processing plants).

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Resistive, reactive, and resistive/reactive earth fault current limiting devices shall comply with AS/NZS 2081.

NOTE: Alternative technologies that provide an equivalent level of safety are not excluded (e.g. arc suppression coils).

When a system consists of multiple transformers, each with its own earth fault current limitation device, and the bus tie(s) between them is (are) closed, the total system fault current consists of the level of current flowing through each of the earth fault current limitation devices added together. This shall be taken into consideration when designing an installation and determining potential voltages that may result as a function of an earth fault within the installation.

2.5 REMOVAL OF POWER AT A CLOSED ELECTRICAL OPERATING AREA Emergency shutdown facilities shall be provided to enable power to be removed from a closed electrical operating area without the need to enter that operating area, e.g. an emergency stop located external or remote to a switch room.

2.6 ELECTRICAL MACHINERY Electrical machinery shall comply with AS 60204.1 and AS 60204.11.

2.7 PROTECTION FROM NON-ELECTRICAL HAZARDS

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Where electrical technology is used to protect people from non-electrical hazards, the equipment and application shall comply with AS 4024 (series), AS 61508 (series), AS IEC 61511 (series), AS 62061 or ISO 13849-1 as appropriate.

2.8 PROTECTION FROM ELECTRICAL HAZARDS 2.8.1 General Interlocking systems shall have a category of protection consistent with AS 4024.1501 or safety integrity level consistent with AS 62061 or performance level consistent with ISO 13849-1.

2.8.2 Interlocking methods Every interlocking system that does not have a rigid mechanical link between the isolating device and the latch on the enclosure being protected shall be designed using functional safety principles.

NOTES: 1 Under-voltage releases, providing the function of ‘no volt, no close’ are the preferred form of electrical release for electrical interlocking.

2 Any circuitry used for electrical interlocking should be ELV or be suitably guarded to protect against inadvertent direct contact.

Where a shunt trip device is the only form of tripping, test facilities to test the integrity of the trip circuit should be incorporated. The trip system shall comply with AS 4024 (series), AS 61508 (series), AS IEC 61511 (series), AS 62061, or ISO 13849-1 as appropriate.

To prevent inadvertent short circuiting of interlock switches, totally enclosed interlock switches of robust construction shall be used. Switch terminals shall be shrouded.

2.8.3 Electrical interlocking for restrained plugs and receptacles Where restrained plugs and receptacles above ELV are used and there is likelihood of a person coming in contact with live pins, provision shall be incorporated to automatically disconnect electricity when the plug is removed. The provision should also prevent automatic restoration of electricity on the insertion of the plug into its receptacle.

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Loss of vacuum/frozen contact protection shall be provided to detect the failure to open of the switching device that supplies the restrained receptacles. Where a switching device is used for the control of restrained outlets, and elsewhere where determined by the risk management process, an upstream switching device shall be fitted with a shunt and/or under-voltage release to remove power from the faulted switching device.

2.8.4 Electrical protection tripping systems for distribution networks Electrical protection tripping systems for distribution networks shall not be disabled by a single undetected failure of the tripping system.

NOTES: 1 AS/NZS 3000 and AS 2067 include particular requirements for electrical protection.

2 Design of the electrical tripping system should be consistent with functional safety principles.

The following considerations apply: (a)

Where a single shunt release is used as the only form of tripping, two energy sources should be used for normal operation. One source may be a stored energy type that is capable of operating the shunt release at least once when the normal power supply is removed.

(b)

The status of the shunt trip coil should be monitored.

Where access to the stored energy device is required, tripping of the circuit-breaker shall occur and access to the stored energy device shall not be possible until the stored energy device has discharged to a safe level.

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2.8.5 Arc flash/blast protection Design shall include provisions for the prevention of arc flash/blast injury. This shall include the positioning of operating handles, explosion vents, integrity and guarding of windows.

NOTES: 1 Consideration should be given to the use of remote switching.

2 For information on arc flash/blast protection, see IEEE 1584 and NFPA-70E.

For remote operation of equipment or plant, such as a circuit-breaker operated by a pendant, the safety of the control shall be taken into account and shall be rated in accordance with a functional safety analysis.

2.9 ISOLATING SWITCHES (DISCONNECTORS) Isolating switches shall be mounted for external operation with a minimum degree of protection to the operator of IP2X to AS 60529.

Isolating switches shall be of the following types: (a)

Fault make/fault break.

(b)

Fault make/load break.

(c)

Off load make/off load break devices.

NOTE: Off load make/off load break devices may be used provided they are equipped with an interlocking device that removes the load before the device is operated and has a suitable category or performance level or safety integrity rating relevant to the risk.

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2.10 CIRCUIT-BREAKERS 2.10.1 General The mounting of the circuit-breaker shall provide for external operation with a minimum degree of protection to the operator of IP2X to AS 60529.

It shall not be possible to re-close a circuit-breaker (including momentary closure, i.e. close-re-trip) that has tripped without first resetting the protection system that caused the circuit-breaker to trip.

NOTE: This may be achieved by systems that have their protection trip interfaced into the motor recharge/closing coil circuit to prevent their operation.

2.10.2 Low voltage distribution boards For low voltage distribution boards containing miniature circuit-breakers, where two or more circuit-breakers are mounted in the same row, the operating mechanism of each shall cause the circuit to open when the operating means are orientated in one general direction.

Where multiple horizontal rows of circuit-breakers are contained within a switchboard, each row of circuit-breakers shall operate in the one general direction, and shall have additional labelling to clearly indicate the ON/OFF position.

2.11 CABLES

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Cables used for power supply and distribution shall be suitable for the intended application, duty and environment including exposure to high temperatures.

Cables that are likely to endure damage to non-protected external insulation during normal operation due to moisture, vibration or mechanical damage shall have metallic screens and/or armouring or shall be provided with conducting elastomeric screens of substantial cross-sectional area so placed as to limit to acceptable levels the touch voltages, as specified in Clause 2.4, and step voltages, as specified in IEEE 80, which may arise in the event of a cable fault.

NOTES: 1 Examples of high vibration areas include process plants and crushing plants.

2 Examples of areas where mechanical damage to insulation can occur include industrial workshops and welding bays.

For low voltage cables, the suitability of the earthing conductor cross-sectional area shall be confirmed in accordance with AS/NZS 3008.1.1.

For high voltage cables, the suitability of the sheath bonding method shall be confirmed in accordance with AS 2067.

2.12 SYSTEM DESIGN 2.12.1 General The supply system shall meet the requirements of cyclic or periodic loads, motor starting, inherent a.c. motor oscillations, transient load changes and regeneration from large motors.

2.12.2 Harmonic sources Harmonic sources such as rectifiers, switch mode power supplies and inverter-fed drives have the potential to create high frequency (capacitive) zero sequence ground currents that flow back to the supply neutral during normal operations.

In cases where neutral earthing impedance is installed, zero sequence currents create a voltage across the impedance. Care should be taken to avoid nuisance trips, alarms, or general maloperation of protection systems. The sizing and rating of the impedance should also be considered to ensure it can handle these currents.

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2.12.3 Supply system to trailing cable and reeling cable fed machinery Touch potentials and step potentials are a function of the resistance of the earth return circuit and the current that flows through the earth return circuit. To minimize the touch and step potentials either— (a)

the resistance of the earth return circuit shall be reduced; or

(b)

the currents that can flow through the earth return circuit shall be limited.

NOTES: 1 Reducing the resistance of the earth return circuit is not always practicable, especially when the fault current can be in the magnitude of thousands of amps or where long runs of cables are required to power mobile or transportable equipment.

Limiting the magnitude of the fault current reduces prospective touch potentials at remote equipment without the need to use large CSA earthing cables. The earth fault current limitation device also has the advantage of reducing touch potentials for all circuits fed from the transformer.

For these reasons the supply system associated with power to mining and quarrying machinery that are supplied via trailing or reeling cables should have earth fault current limitation, i.e. an impedance earthed IT system.

2 For details of the IT system and other systems, see Appendix A.

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2.12.4 Switch mode power supplies Switch mode power supplies are widely used. Numerous electric shocks have occurred on mine sites (involving vending machines, battery chargers and welders) when the earth connection has been compromised. The EMC/RFI filters within these machines utilize the protective earth as a discharge path for the filter; if the earth connection is lost, the discharge path can be to the frame of the device, resulting in the potential of the frame rising above earth.

Care shall be taken to ensure that the machine is installed within an appropriate environment, and the maintenance scheme concentrates on ensuring the integrity of the earth connection.

2.13 GENERAL REQUIREMENTS FOR ELECTRICAL COMPONENTS 2.13.1 Relevant Standards The electrical specifications of all components shall be not less than that required by the relevant Australian or IEC Standards.

2.13.2 Design and selection Design and selection of components shall be on the basis of expected loading, operating characteristics and cyclic duty, taking into consideration the protection required in special and arduous environmental, operational, transportation and storage conditions.

Some of these conditions are as follows: (a)

High altitude.

(b)

Low and/or high ambient temperature.

(c)

Supply voltage variations.

(d)

Supply frequency variations.

(e)

Insecure power supply and transients.

(f)

High or low humidity.

(g)

Environment, e.g. dust, wind pressure, marine atmosphere.

(h)

Flammable and/or explosive materials and/or atmospheres.

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(i)

Vermin, including rodents or other small animals.

(j)

Localities prone to natural catastrophes.

(k)

Ecological impact.

(l)

Corrosive environments.

(m)

Wet/hose down-environments.

(n)

Ultraviolet light.

AS/NZS 3007:2013

In order to ensure that correct design parameters are selected, mutual agreement shall be reached between the user and the supplier as to the quantitative and/or qualitative conditions.

Equipment shall be applied, installed, and operated in accordance with the manufacturer’s instructions.

The temperature rating of all selected electrical/electronic equipment to be installed within an enclosure shall be suitable for use at the operational temperature within the enclosure, at maximum load.

2.13.3 Construction of components and enclosures Design shall incorporate features to deal with arduous handling and transportation conditions to which the equipment is to be subjected. Suitably rated lifting and towing points, skid bases, fork lift facilities, etc., shall be included in the design.

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The design of all enclosures shall provide operator safety by means of— (a)

doors, fixed panels and partitions to prevent contact with live conductors and exposure to arcing products;

(b)

an enclosure rated to contain or control the effects of the prospective fault energy;

(c)

vents located in a position to direct any arc products away from the operator; and

(d)

pressure relief to atmosphere so that any abnormal pressures that develop are directed away from the operator.

Enclosures shall have a minimum degree of ingress protection in accordance with AS 60529 appropriate for the installation location and conditions.

Unused openings and threaded entries shall be closed or plugged so the degree of ingress protection of the enclosure is maintained.

2.13.4 Terminals The majority of mining cables have flexible multi-stranded conductors. The different cross-sections and manufacturer’s recommendations are relevant when selecting the dimensions of the terminals and crimp lugs to which they may be connected.

2.13.5 Measuring instruments Measuring instruments shall not be connected into any protective circuit such that the measuring instrument may impair the operation of the protective circuit.

2.13.6 Isolation of data and communication lines Where data communications devices are used they shall be arranged to minimize the coupling of hazardous voltages onto data communications lines.

In particular, data modems that connect or couple to power cables shall be suitably rated for the application and type tested to withstand the expected voltage range.

NOTES: 1 This should include consideration of any coupling to any energized circuits at remote locations and possibly different voltages to ensure these circuits are effectively isolated.

2 For guidance on low level signal and communication systems, see Appendix C. COPYRIGHT

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2.13.7 Clearance and creepage Design of electrical equipment shall take into account the arduous environment in which the equipment is to be installed. Clearance and creepage shall be appropriate for the level of moisture and pollution that the electrical equipment is likely to be subjected to. The minimum distances for clearance and creepage shall be in accordance with Table 2.1.

NOTE: For details of the degree of pollution expected in particular locations, see AS 4436.

TABLE 2.1 MINIMUM CLEARANCE AND CREEPAGES IN AIR Clearance of creepage, mm ≤15 V

300 V

600 V

1000 V

3300 V

Clearance phase-to-phase direct

3

5.5

8

14

51

89

127

Clearance phase-to-earth direct

3

5.5

8

14

51

64

76

Creepage phase-to-phase over insulation

5

10

20

32

76

146

216

Creepage phase-to-earth over insulation

5

10

20

32

51

89

127

6600 V 11000 V

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NOTES: 1

Clearances and creepages ≤ 1000V are derived from AS/NZS 3439.1:2002.

2

It should be realized that any tabulation of pollution characteristics cannot cover the complete range of pollution possible and hence it may be necessary, in particular cases, to increase creepage distances for the special pollution encountered. Consideration should also be given to the possibility of varying pollution levels due to seasonal changes and exceptional climatic conditions.

3

Except for Pollution degree I as defined in AS.NZS 3439.1, condensation of water will always be considered arising from either— (a) the temperature of the insulation surface falling below the dew-point of the surrounding air; or (b) hygroscopic dust or salt contamination causing moisture to deposit at low relative humidity.

4

Conductive dusts may originate from the environment (e.g. material being mined or processed), or from within an enclosure (e.g. dust from carbon or metallic brushes).

5

The voltage corresponds to the system highest voltage (phase-to-phase).

6

This Table supplements the creepage and clearance requirements of AS 2067.

2.13.8 Information requirements A Safety File (or Verification Dossier) shall be maintained over the life cycle of all electrical equipment, to provide traceable evidence relating to the safety of the equipment over each of the phases of the life cycle, and provide a reference to consider prior to carrying out any upgrades, modification or changes to maintenance practices.

NOTES: 1 The information may be supplied by manufacturers and overhaul service providers, and some may be operationally managed by the mine operators.

2 For a list of topics that should be taken into consideration, see Appendix E.

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S E C T I O N 3 P R O T E C T I O N A G A I N S T O V E R L O A D S A N D F A U L T S 3.1 INTRODUCTION 3.1.1 General This Section sets out the minimum requirements for protection against overcurrent in respect of overload protection and short-circuit protection, together with the coordination of overload and short-circuit protection and the coordination of this protection with the conductors and apparatus.

Earth fault protection on earth fault restricted systems is specifically covered.

This Section supplements the requirements of AS/NZS 3000, AS 2067, AS 60204.1 and AS 60204.11.

NOTE: For information on the types of protective devices and their maintenance, see Appendix B.

3.1.2 System fault levels

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Consideration shall be given to the fault levels of electrical circuits to ensure the electrical equipment and cabling are rated for the system fault level.

NOTES: 1 Any protection study undertaken should take into consideration the effects of minimum and maximum possible fault levels.

2 Overcurrent protection arrangements should take into consideration the reduction of risk from arc flash and blast by ensuring short-circuit faults are detected at the minimum practicable current and the fault cleared in the quickest possible time.

3 The use of impedance earthed IT systems and the potential advantages in reducing arc flash risks are given in Paragraph A5.1, Appendix A. 4 The use of arc-detection devices or other specialist arc flash protection devices may reduce the impact of an arc flash/blast event.

3.2 GENERAL RULE Electrical equipment and live conductors shall be protected by one or more devices for automatic interruption of the supply in the event of overcurrent due to overload and shortcircuits except as identified in Clause 3.3.

Protection against overload and against short-circuits shall be coordinated in accordance with Clause 3.4.

3.3 AUTOMATIC INTERRUPTION—PROTECTION AGAINST OVERCURRENT DUE TO OVERLOAD Any electrical equipment which may cause overcurrent due to overload should be provided with an overload protective device to automatically interrupt the supply to the equipment.

Devices for protection against overcurrent shall not be provided for circuits where unexpected opening of the circuit could cause a danger greater than overcurrent.

NOTE: Examples of such circuits are certain safety system supplies, lifting magnets, exciter circuits of machines and the secondary circuits of current transformers. In such cases the provision of an overload alarm is strongly recommended.

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Overload protective devices should not be installed in conductors supplying electrical equipment where the unexpected opening of the circuit could cause a danger greater than not opening the circuit. Such cases may include but not be limited to the following: (a)

Excitation circuits for d.c. and a.c. (synchronous) motors.

(b)

Supply circuits of lifting magnets.

(c)

Current transformer secondary circuits.

(d)

Fire service pumps and certain drainage pump installations.

(e)

Elevators (lifts).

(f)

Hoists.

(g)

Special hydraulic pumps.

(h)

Excavator main drives.

(i)

Certain conveyors.

(j)

Certain braking circuits.

(k)

Emergency lighting and signalling.

(l)

Certain drainage pump installations.

NOTE: Where thermal overload protection is not provided in the above examples, additional fire proofing measures should be considered, for example, oversized or fire-resistant cabling.

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3.4 COORDINATION OF OVERLOAD AND SHORT-CIRCUIT PROTECTION AFFORDED BY SEPARATE DEVICES Where the short-circuit and overload protection is provided by separate devices, the characteristics of the devices shall be coordinated so that the breaking capacity of the overload device is not exceeded.

3.5 EARTH FAULT PROTECTION ON IMPEDANCE EARTHED IT SYSTEMS Earth fault protection shall be provided on all impedance earthed IT systems except as allowed for in Clause 11.3 (see Note 1).

Where an earth fault current limitation device is not continuously rated, it shall be protected by duplicate protection schemes (see Note 3).

NOTES: 1 The ratio of earth fault current-to-earth fault protection trip should be as high as practical, whilst taking into consideration nuisance tripping caused by capacitive current.

Mechanical failure of an earth fault limitation device caused by vibration, shock, corrosion, insulation failure or external force applied to terminals can cause an IT system to become— (a) open circuit and thus disconnected from the earth reference; or (b) shorted to earth thus bypassing all or part of the impedance of the device and therefore increasing the value of the prospective earth fault current.

The thermal failure of an earth fault current limitation device can cause an IT system to become disconnected from the earth reference.

The above scenarios present extremely dangerous outcomes that can ultimately lead to the inability to detect an earth fault or increased touch and step potentials or cascaded system insulation failure.

2 Consideration should be given to the installation of an NER integrity monitoring device complying with AS/NZS 2081.

3 Continuously rated earth fault limitation devices are not normally manufactured above 25A.

Earth fault current limiting devices should be inspected annually.

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Following the activation of a backup earth fault protection scheme, the earth fault current limiting device shall be inspected unless an NER integrity monitor is fitted.

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Consideration should be given to utilizing duplicate systems for earth fault protection.

NOTES: 1 Examples of duplicate protection schemes include the following: (a) Utilizing two current transformers, two separate earth fault protection relays, and duplicate fault clearing mechanisms. (b) Single earth fault protection scheme and negative phase sequence protection scheme upstream which operates a separate fault clearing mechanism. (c) Single earth fault protection scheme and negative phase sequence protection scheme upstream.

2 Examples of duplicate fault clearing mechanisms include the following: (a) Duplicate series circuit-breakers. (b) Dual trip coils on single circuit-breaker. (c) Schemes based on circuit-breaker fail principles.

3 The assessment may take into consideration a 10:1 trip ratio with a time delay as a backup to a primary non-delayed trip at a lower trip ratio.

4 During the inspection of an earth fault current limitation device, particular attention should be paid to the condition and integrity of earth and neutral terminal bushings, bolted connections, and corrosion on the element and any welds within the device. Applying a current significantly less than the let-through value of the device in order to measure the resistance and therefore make an assessment of the integrity of the device, without an additional physical inspection, is not a reliable means of assessment.

5 Further information on the installation and use of earth fault protection systems is given in AS/NZS 2081.

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S E C T I O N 4 E L E C T R I C A L W I R I N G E Q U I P M E N T A N D M A C H I N E R Y

O F

4.1 GENERAL This Section applies to the following: (a)

Machinery which is capable of being readily moved about whilst it is in operation, e.g. flexible conveyors, electric face shovels, draglines and overburden drills.

(b)

Fixed and mobile processing plant (grinding circuits, mills, crushers, thickeners, etc.).

(c)

Refineries.

Electrical equipment of machinery and associated accessories shall be well constructed, rugged, based on sound engineering principles and designed in a manner that will facilitate inspection and maintenance.

Components shall be designed to meet such conditions as vibration, acceleration, deceleration, slewing and angles of inclination (tilting and mounting), which may occur under expected operational conditions.

Enclosures with withdrawable and plug-in equipment on such machinery as draglines and face shovels shall be constructed so the equipment modules cannot be dislodged from their position during normal operation. Withdrawable and plug-in equipment containing power circuits shall not operate unless fully engaged.

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4.2 ELECTRICAL ISOLATION Isolating facilities by means of which all power to the machinery can be isolated for the purpose of carrying out electrical work shall be provided.

The isolating facilities shall be capable of being locked in the isolated position.

The isolating facilities shall be either in a separate compartment or remote from the machinery to isolate the supply cable.

4.3 ISOLATING FOR MECHANICAL MAINTENANCE An isolating device to isolate all power to the machinery for the purposes of carrying out non-electrical work on the machine shall be provided.

The main isolating device shall isolate all electrical power circuits that may affect movement.

NOTE: On the load side of the isolating device, functional switching devices may be used for individual drives or groups of drives.

4.4 REMOTE CONTROL Remote control of mobile machinery shall comply with the AS/NZS 4240 series.

NOTE: It is not intended that the AS/NZS 4240 series be applied to equipment not covered by the scope of that series.

4.5 PENDANT CONTROL (UMBILICAL CORD) Pendant control of mobile machinery should comply with the AS/NZS 4240 series.

NOTE: It is not intended that the AS/NZS 4240 series be applied to equipment not covered by the scope of that series.

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4.6 CABLING 4.6.1 Single-core cables Single-core cables which are installed in intimate contact in a common duct, conduit or sleeving may be used for both power and control circuits. All such cables shall be insulated for the maximum voltage applied to any cable in the duct, conduit or sleeving.

When using single-core cables for alternating current circuits, all conductors of a given circuit shall follow the same magnetic path to neutralize the resultant magnetic flux.

NOTES: 1 For recommendations relating to the segregation and/or screening of cables to minimize interference to low signal level systems and communication systems, see Appendix C. 2 For the correct arrangement of phase, neutral and protective earth conductors in single-core wiring systems, see AS/NZS 3008.1.1.

4.6.2 Machinery cables

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The following requirements apply to all cables installed external to an electrical enclosure on mobile machinery: (a)

They shall be arranged clear of moving parts.

(b)

They shall be protected from hot surfaces that may adversely affect the insulation of cables.

(c)

They shall be arranged so as to prevent excessive bending or twisting.

(d)

They shall be clamped in place to prevent undue movement.

(e)

They shall be protected from mechanical damage by being correctly positioned within the body of the machinery.

(f)

They shall be impervious to or be protected from ultraviolet degradation.

(g)

They shall be protected from hydraulic lines and abrasions.

(h)

They shall be of the same temperature rating or higher as the environment in which they are installed.

NOTE: Consideration should be given to possible sheath and insulation damage due to the presence of oils, greases and other fluids and materials.

4.7 ROTATING ELECTRICAL MACHINES 4.7.1 Mechanical construction Rotating machines used in applications where high acceleration, overspeed, reversing or braking may be employed shall be designed and constructed so as to withstand expected stresses that may occur to parts such as rotor windings or cages, stators, stator end windings, shafts and couplings.

4.7.2 Guarding Electrical rotating machines shall be so located or guarded as to prevent inadvertent contact with moving parts.

NOTE: Guarding should be in accordance with the AS/NZS 4024 series.

4.7.3 Particular features For rotating electrical machines, the following should be taken into consideration: (a)

Accessible connections to motor leads or terminals, including earth connection.

(b)

Devices that secure screwed covers into place so that unauthorized persons cannot unscrew the cover.

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Lifting lugs to facilitate handling on and off the machinery.

NOTE: In general, the eye provided on a motor is not rated for lifting the motor. For means to lift the motor, the supplied technical information should be consulted.

(d)

Adequate mounting fixings or supports, with reasonable access to all fasteners, which are required for routine inspection and maintenance.

(e)

Avoidance of entries that will allow water to enter the motor enclosure during normal operating conditions.

NOTE: It may necessitate consideration of protection in the machinery design to prevent a direct fall of water on motors.

4.7.4 Variable speed drives Variable speed drives shall comply with IEC 61800-5-1 and IEC 61800-5-2.

NOTE: Refer to Appendix D for information on variable speed drives.

4.8 MOBILE MACHINERY CABLE ATTACHMENTS Attachments should be provided for anchoring trailing cables where the cable attaches to the machinery.

The design should allow for all machinery movements to minimize the risk of cable damage. Where the cable is secured to allow reeling of the cable, means should be provided to reduce shock loading on the cable in excess of the safe working load of the cable.

4.9 CABLE REELS

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4.9.1 Introduction Cable reel drums and bending radii for reeling cables (frequently reeled on and off a cable drum) shall be designed according to Clause 4.9.2 to 4.9.5.

4.9.2 General Cable reel drums shall comply with AS 60204.1 and for high voltage machinery with AS 60204.11.

The driven reel shall maintain positive tension on the trailing cable during reeling and unreeling operations. The tension shall be within the cable manufacturers’ specified operating tensions under all operating conditions.

Cable reel bearings shall not be an integral part of a circuit for transmitting electrical energy nor form part of the earthing circuit.

NOTE: Cable reel drums should be designed to prevent undue bending of cables outside the cable manufacturers’ specified operating bending radius for continuous reeling and sheathing duty.

4.9.3 Drum rating factors Provision should be made in the design of ventilated cylindrical cable reel drums to space each turn apart by at least 10% of the cable diameter.

4.9.4 Permissible reductions in cable reel drum diameters A reduction of the cable reel drum diameter with consequent reduction of cable life may be employed where critical space limitations on certain plant, such as in winning machinery or conveyors, preclude the use of the limiting values specified in AS 60204.1. Similar reductions may be employed where cables are specifically designed for the arduous duty associated with certain specialized equipment or where cables are reeled infrequently.

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4.9.5 Cable reel interlock limit Cable reels shall be fitted with a protective device to stop the machinery travel. The functionality of the protection device shall be determined by the risk management process.

The protective devices shall operate in the event that— (a)

the cable exceeds the maximum safe limit of cable on the reel (over fill limit);

(b)

the quantity of cable falls below the minimum safe limit (run out limit); or

(c)

the cable reel is in contact with the ground and the cable will be damaged if the cable reel continues to rotate (jacking limit).

The above mentioned devices shall— (i)

automatically bring the machinery safely to a stop and apply the brakes; and

(ii)

be part of a control circuit so arranged that resetting of the device does not automatically restart the machinery.

The above requirements do not apply to machinery within a defined boundary, e.g. trackmounted stackers and reclaimers.

4.10 MOBILE MACHINERY LIGHTING SYSTEMS Mobile machinery shall be provided with a lighting system that is appropriate for the machinery’s operation.

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Design of machinery lighting shall consider the effects of light pollution on machinery operators and affected neighbours.

Lighting circuits shall be arranged with emergency lighting or multiple circuits to ensure sufficient lighting is available during partial or total power loss.

NOTE: The design and installation of emergency escape lighting and exit signs should take into consideration AS 2293.1.

4.11 CONTROL CIRCUITS AND CONTROL DEVICES 4.11.1 Control, protection and auxiliary conductors Where there is a reduction of cross-sectional area of conductors connecting the power source to an auxiliary circuit protective device, the conductors shall be double insulated and as short as practicable.

4.11.2 Centre tapped control circuits Where the control supply is earthed via the centre tap of a transformer, operating coils shall not hold in at a voltage that exists between one leg and the earth point.

NOTE: This may require the addition of further protection such as 30 mA earth leakage protection or insulation monitoring where the control circuit extends to field devices.

4.11.3 Unearthed control circuits For unearthed control circuits, measures shall be implemented which ensure in case of normal operating conditions with no circuit faults that, after an operational switch-off, the total current flowing through the closing coil of a switching device shall be less than the current needed for holding the switched-on position of the switching device.

This total current shall also be less than the drop-out current of the switching device with the smallest drop-out current. This total current includes those currents caused by capacitance and leakage to earth and capacitance and leakage between the cores of the control circuit.

The value of the drop-out current for the switching device in use shall be measured and used as a basis for determining the total permissible capacitance and leakage currents, which shall not exceed 70% of the drop-out current.

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4.11.4 Earthed control circuits For earthed control circuits where a single-pole switch(es) is used for actuating the control device, the switch(es) shall be in the phase conductor to the device. The neutral conductor shall be directly connected to the other terminal of the device. Double-pole switch(es) may be used for actuating the control device provided that they operate simultaneously in both the phase and neutral conductors.

After an operational switch-off—in the case of normal operating conditions with no circuit faults—the total current flowing through the closing coil of a device shall be less than the current needed for holding the switched-on position of the device. This total current shall be less than the drop-out current of the device having the smallest drop-out current. The total current includes those currents caused by capacitance and leakage between the cores of the control circuit.

The value of the drop-out current for the device in use shall be measured and used as a basis for determining the total permissible capacitance and leakage currents which shall not exceed 70% of the drop-out current.

4.11.5 Control device location Controls on all machinery shall be located so they are within easy reach of the operator.

NOTE: Consideration should be given to sound ergonomic principles for location and means of operation.

Where dual-driving cabs are fitted to machinery (e.g. draglines and EWPs), a control direction device shall be fitted and set to give control to one driving cab and to immobilize the controls in the second driving cab.

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4.11.6 Synchronous motor control 4.11.6.1 Automatic discharge of field energy Where synchronous motors are used, provision shall be made for automatic discharge of the field energy (i.e. field removal or suppression) upon disconnection of the motor.

4.11.6.2 Automatic field excitation control Where synchronous motors are used to drive periodic or cyclic loads (a type of duty in which operation whether at constant or variable load is regularly repeated), an automatic field excitation control is recommended.

4.11.6.3 Power loss protection Where synchronous motors are used to drive loads which may be regenerative, means shall be provided to trip the motor starting switch or incoming line switch upon loss of power supply.

NOTE: Frequency-sensitive devices are recommended.

4.11.7 Dead man control Where a ‘dead man control’ is required, its operation shall stop travel movement and bring the machinery safely to rest.

NOTE: The principles described in AS 4024 (series) should be used in the design of the control.

4.11.8 Start controls Where equipment is started manually from one or more locations, or is started automatically, a suitable audible warning device, together with appropriate notices, shall be provided to give advance warning of equipment starting, unless one or more of the following conditions apply: (a)

Guarding is provided to prevent personnel access to hazardous parts.

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Danger to personnel does not exist from equipment starting.

NOTE: For sequential starting of a localized plant group, a single warning system may be sufficient.

The audible alarm shall sound for a specified time (determined by a risk management process) before any movement occurs; in addition visual alarms may be required.

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The alarms shall be operational regardless of what form of control has been selected.

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S E C T I O N 5 T R A N S P O R T A B L E / R E L O C A T A B L E D I S T R I B U T I O N A N D C O N T R O L E Q U I P M E N T 5.1 GENERAL 5.1.1 Issues This Section covers distribution and control equipment which is required to be moved from place to place between periods of operation.

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The types of issues commonly associated with the use of this type of equipment on a mine or quarry include the following: (a)

The movement of the equipment around the site.

(b)

The verification of the design after relocation.

(c)

The supply of trailing cable fed machinery from a significant amount of this equipment.

(d)

The control of touch voltages.

(e)

The control of transfer voltages due to earth potential rise.

(f)

Lightning protection.

(g)

The operation of switchgear in a confined area.

(h)

The change of operating location and the resulting impact on system characteristics including verification of the electrical protection devices settings under the new conditions and location within the network.

(i)

The ability to supply power to a variety of loads.

(j)

Potential variability in the voltage at the point of connection and/or in the equipment being supplied.

(k)

The emergency removal of power.

(l)

Access to high voltage equipment.

(m)

Proximity to shot firing operations with respect to direct damage from overpressure waves, fly rock and excessive vibration.

(n)

Control of documentation.

5.1.2 Enclosures Enclosures shall comprise single or multiple compartments, each fitted with suitable covers or access covers.

NOTE: Enclosures should incorporate facilities for lifting and transport.

Where enclosures are required to be coupled together, the coupling arrangement shall prevent, in normal use, undue strain being placed on any busbars, flanges or interconnecting cable coupling devices.

5.1.3 Means of isolation A means shall be provided to isolate all circuits above extra-low voltage (ELV).

All isolators shall be externally operated and fitted with lockout facilities. The switched position and function of all isolators shall be clearly labelled.

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Auxiliary circuits that are required to remain energized while the main power is isolated, such as lighting and power sources, shall be provided with a means of isolation. These auxiliary circuits shall only remain energized while the main power is isolated, provided such equipment and cabling associated with the auxiliary circuits are not housed in the same compartment(s) as equipment isolated by the main switching device.

5.1.4 Location of explosion vents Particular care should be taken with the location of explosion vents on transportable equipment due to the different methods of access compared to fixed equipment.

5.1.5 Positioning of outlets All outlets shall be positioned to allow ease of connection, removal of plugs, adequate bending radius of cables and ready access to outlet controls.

5.1.6 Lighting Area lighting should be considered to improve the visibility of outlets, indicators, labels and instructions.

5.1.7 Internal wiring Through-conductors shall maintain the same phase polarity and phase rotation on any extension supply.

5.1.8 Control, protection and auxiliary conductors

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Where there is a reduction of cross-sectional area of conductors connecting the power source to an auxiliary circuit protective device, the conductors shall be double-insulated and as short as practicable.

5.1.9 Monitoring protective conductor continuity in trailing cables Continuous continuity monitoring should be provided for the protective conductor of trailing cables supplying mobile machinery. Where such monitoring is used, the operating coils shall not be inserted in protective conductors.

5.2 TRANSPORTABLE SUBSTATIONS 5.2.1 General requirements For substations supplied at 11 kV or below, substations constructed in accordance with AS/NZS 4871.3 may be used.

If cable droppers are used to provide high voltage supply to the transportable substation, the droppers shall be affixed to the powerline by suitably designed clamps and shall be provided with additional mechanical support to prevent tension to the electrical connection of these clamps.

NOTES: 1 These substations are commonly used to supply trailing cable fed mobile machinery and underground workings. They should be fitted with a form of earth fault current limitation.

2 For typical electrical protection arrangements and a diagrammatic example (see Figure B1, Appendix B).

5.2.2 Earthing terminals Provision shall be made on each enclosure of the substation for the attachment of an external earthing terminal. There shall be at least two accessible terminals for connection to any associated earth grids/stakes. Earthing terminals shall be bonded together via copper straps or flexible conductors.

NOTE: The recommended minimum bonding conductor cross-sectional area (CSA) is 70 mm 2.

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5.2.3 Primary switchgear Circuit-breakers or combination fuse switch (CFS) units shall be provided in conjunction with protection devices to provide a means of protection against a range of fault conditions.

NOTE: Circuit-breakers are preferred.

5.2.4 Primary protection Where utilized, the following protection shall clear the primary protection device of the transformer: (a)

Short-circuit.

(b)

Overload.

(c)

Transformer differential.

(d)

Backup secondary side earth leakage.

(e)

Circuit-breaker loss of gas/vacuum.

(f)

Transformer over-temperature.

(g)

Transformer loss of gas, if gas pressurized.

(h)

NER integrity monitor.

(i)

Bucholz relay.

(j)

Overpressure switch.

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For short-circuit, earth-leakage and loss of gas/vacuum trips, a positive means of fault diagnosis shall be provided to identify individual fault trips after loss of power.

5.2.5 Transformers 5.2.5.1 General Power transformers shall comply with AS 60076.1 or equivalent.

NOTE: Electrostatic shielding between primary and secondary windings should be considered.

5.2.5.2 Core, coil and tank bracing The core and coils of the transformer shall be securely clamped in order to ensure the whole assembly is sufficiently rigid to withstand any electrical or mechanical stresses, caused by the arduous cyclic duty and vibration, which may occur in service and when being transported around the mine.

Guides, locating lugs or a combination of both, shall be mounted with adequate fixing bolts inside the tank to register the location of the core.

NOTE: Means for attaching lifting tackle should be provided on the core frame.

5.2.5.3 Enclosures Any transformer breather or pressure-relief means shall be fitted in such a way as to minimize degradation of the cooling medium (coolant) through condensation.

5.2.5.4 Off-load tap changing Off-load tap changers shall— (a)

have all positions clearly marked;

(b)

be visible from a safe position; and

(c)

have provision for securing in any position.

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Where a hand-wheel-operated tap changer is used, it shall be designed to suit the rated temperature and have provision to ensure it cannot be left in any position other than one of the tap positions.

Where bolted links are used, they shall be arranged to avoid incorrect connection.

Any internal connections, including transformer bushing, shall be rated to suit the operating temperature.

5.2.5.5 Oil containment Where there is no environmental or safety risk, oil bunding is not required.

5.2.6 Secondary protection

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The following protection shall be provided: (a)

Short-circuit.

(b)

Overload.

(c)

Earth leakage.

(d)

Earth continuity for— (i)

trailing and reeling cable supplies; and

(ii)

where restrained receptacles are used.

NOTES: 1 For impedance earthed IT systems, AS/NZS 2081 details the design and construction requirements for earth continuity and earth fault protection devices.

2 Consideration should be given to the use of earth fault lockout protection (see AS/NZS 2081).

3 Consideration should be given to the use of frozen contact protection (see AS/NZS 2081).

4 Consideration should be given to the use of under-voltage trip systems on the secondary side.

5.2.7 Labelling The following labels are required: (a)

Operational instructions.

(b)

Where a lifting facility of a subassembly is not capable of being used to lift the complete substation assembly, labelling shall be provided to warn/prevent them being used after the substation is assembled.

(c)

Identification of outlets. A durable label shall be placed adjacent to and in an unambiguous location for each of the cable connection facilities, as follows: (i)

For the supply connection other than OHL droppers.

DANGER—HIGH VOLTAGE SUPPLY CONNECTION THIS CONNECTION IS NOT ISOLATED BY THIS CIRCUIT-BREAKER

(ii)

For the extension supply (through going or ring main supply).

DANGER—HIGH VOLTAGE EXTENSION SUPPLY CONNECTION THIS CONNECTION IS NOT ISOLATED BY THIS CIRCUIT-BREAKER

(d)

Identification of switching devices.

Labelling shall be clear and unambiguous.

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5.3 DISTRIBUTION AND CONTROL EQUIPMENT For distribution and control equipment supplied at 11 kV or below, equipment constructed in accordance with AS/NZS 4871.2 may be used.

For equipment supplied at higher voltages, the following applies: (a)

The equipment shall comply with AS/NZS 4871.2.

(b)

If cable droppers are used to provide high voltage supply to the transportable substation, they shall be affixed to the powerline by suitably designed clamps and shall be provided with additional mechanical support to prevent tension to the electrical connection of these clamps.

NOTE: For typical electrical protection arrangements, see Appendix B.

5.4 FLEXIBLE CABLE TERMINATION BOXES Where a practicable cable plugs shall be utilized for cable joining.

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Where cable plugs cannot be used, the following measures shall be taken: (a)

High voltage clearances and wiring segregation shall be maintained.

(b)

Ingress protection levels shall be suitable for the environment.

(c)

Ergonomics shall be suitable to allow easy handling of cables connected to the termination box.

(d)

Termination boxes shall be either lockable with a suitable keying system restricting access, or fitted with a trapped keyed interlocking system that only permits access after the source of supply has been isolated.

(e)

Where practicable, a pilot system interlocked to the main compartment door of the termination box, so that the supply to the trailing cables is removed if the door is opened, shall be utilized.

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S E C T I O N 6 F L E XI B L E F E E D E R , T R A I L I N G A N D R E E L I N G C A B L E S E L E C T I O N , A P P L I C A T I O N A N D U S E 6.1 DESIGN OF CABLES 6.1.1 AS/NZS 2802 compliant cables Cables should comply with AS/NZS 2802.

6.1.2 Phase conductors Selection of phase conductor size should take into consideration the expected load current, short-circuit current and duration of fault, voltage drop and the mechanical strength required for the expected method of handling. The voltage drop should be calculated for both starting and maximum load conditions. Where supplying cyclic loads, the currentcarrying capacity should be based on the long time, e.g. 10 min r.m.s. current expected.

6.1.3 Protective conductor

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All multicore cable of the flexible feeder, reeling and trailing types shall contain a protective conductor. In high voltage systems, special measures shall be taken to guard against deterioration of the earthing circuit.

NOTE: This may be achieved by the following: (a) Monitoring the protective conductor against increase in resistance by the use of pilot cores, high-frequency monitoring or other means. (b) Using cables in accordance with manufacturer’s specified tension limits and bending radii limits. (c) Using a protective conductor in the form of core(s) and/or screen(s).

For certain classes of flexible feeder cables, the armouring may, subject to the requirements of Clause 6.1.3, form the protective conductor.

6.1.4 Armouring as protective conductor Where the cross-sectional area of a single composite strand of the armouring is greater than 6 mm2, the metallic armouring of a flexible feeder cable may be used as the protective conductor, provided— (a)

the security against breakage of the armouring (taking into account strength, elongation, lay, etc.) is at least equal to that of all the conductors; and

(b)

the armour conductivity is at least equal to that of a protective conductor of the required nominal cross-sectional area which would otherwise be required.

6.1.5 Protection against partial discharge Partial discharge testing shall be conducted in accordance with AS/NZS 2802.

For flexible cables having nominal voltages greater than 4000 V, measures shall be provided to minimize internal partial discharge or to render such effects harmless (e.g. field gradient control).

6.1.6 Semi-conducting layers Where cables are fitted with substantial longitudinal semi-conducting layers for the purpose of providing a current path to the protective conductor in the event of a fault, the resistance between the semi-conducting element and the protective conductor should be tested to ensure that it is suitable to carry the prospective fault current.

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6.1.7 Provision of screens and/or armouring for cables above 1000 V High voltage cables shall have metallic screens and/or armouring or shall be provided with conducting elastomeric screens of substantial cross-sectional area and so placed as to limit the touch and step voltages that may arise in the event of a cable fault to acceptable levels as defined in Clause 2.4.

6.1.8 Segregation of power and control cores 6.1.8.1 Multicore cables

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Multicore cables containing power and control cores shall comply with the following requirements as appropriate: (a)

Any cable containing pilot, control and supervisory cores shall have such cores insulated from all other conducting elements of the cable.

(b)

Any cable containing pilot cores shall contain semi-conductive or metallic screen barriers to prevent the transmission of high voltage onto the pilot core under fault conditions.

(c)

Cables operating at high voltage on an IT system shall have either metallic screens or individual conductive rubber screens separating the power cores from the other core(s).

(d)

Cables operating at high voltage on an earthed system (TT or TN systems) shall have metallic screens separating the power cores from the other core(s).

(e)

Manufacturers’ recommendations shall be followed for the installation and operation of these cables.

Cables operating at low voltage shall have pilot, control or supervisory cores separated from power cores by conductive rubber or metallic screens if on an IT system, or metallic screens if on a TT or TN system. Alternatively, for either system, the pilot, control or supervisory cores shall be insulated to a voltage level equal to that of the power cores.

6.1.8.2 Composite multicore cables on reeling drums Multicore cables which contain power, pilot, control or supervisory cores may be used for reeling drum applications, provided the cable is specially designed for such reeling duty.

6.1.8.3 Compliant cables Cables complying with AS/NZS 2802 are deemed to comply with the requirements for segregation of power and control wires.

6.1.8.4 Repair of cables Cable repairs shall be in accordance with AS/NZS 1747.

6.2 POWER CABLE TWIST LIMITATION Where the normal mode of operation of the machine requires infrequent rotation through an arc of up to 360 degrees in either direction, the distance between the clamping supports of the cable shall be not less than 50 times the largest cable diameter in the cable run.

Where the normal mode of operation of the machine requires frequent rotation through an arc of up to 360 degrees in either direction, the distance between the clamping supports of the cable shall be not less than 100 times the largest cable diameter in the cable run.

Where cables designed especially for flexible feeder, trailing and reeling are used, the above ratios may be reduced to 25 and 50 times respectively.

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6.3 CABLE CONNECTORS Where plug and socket connectors are used at voltages above 1000 V, measures shall be taken to prevent the plug from being engaged with, or disengaged from, the socket while the circuit is energized.

The measures shall consist of one or more of the following: (a)

The provision of isolating switches which are interlocked with the plug/receptacle so as to prevent connection or disconnection while the circuit is energized and to prevent switching the circuit when the plug/receptacle connection is incomplete.

(b)

The provision of protective conductor monitoring by means of a pilot core, high-frequency monitoring, or other means.

NOTE: This measure is intended as a safety feature and should not be used for normal isolation purposes.

(c)

Implementation of suitable operational procedures such as the use of plug/receptacle connectors requiring a special tool for disengagement.

Bolted couplers shall be designed so the most likely fault is a phase-to-earth fault (e.g. inter-phase earthed barriers).

6.4 MOVING CABLES 6.4.1 Cable management plan

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Where determined by risk assessment, a cable management plan shall outline the requirements for moving and handling cables.

NOTE: As part of the cable management plan, the following should be taken into consideration: (a) Protection of cables. (b) Maximum tensions to be applied to trailing cables. (c) Minimum bending radii for trailing cables. (d) Trailing cable roadways. (e) Anchoring of trailing cables. (f) Storage of trailing cables. (g) Transporting of trailing cables. (h) Snigging of trailing cables. (i) Cable tower and high wall gantries. (j) Manual handling of trailing cables. (k) Additional protection requirements for trailing cables.

6.4.2 Flexible cable risks All mineworkers who handle cables or who work in close proximity to cables or cable accessories are exposed to the hazards of— (a)

manual handling of heavy, awkward cables and associated accessories;

(b)

electric shock through direct or indirect contact as a result of working with damaged trailing cables; and

(c)

uncontrolled release of energy through short-circuits (arc blast).

The most common causes of failure in trailing or reeling cables are crushing or other similar mechanical damage, constant bending or flexing inside the minimum bending radius, excessive tension, sheath wear resulting from abrasion, and ingress of moisture.

Table 6.1 sets out some typical risks and their causes.

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TABLE 6.1 TYPICAL RISKS AND CAUSATION Typical risks Direct contact with cable conductors or parts of cable accessories such as plugs or couplers

Typical causes Damaged cable or plugs exposing live conductors and protection fails to detect the damage and automatically disconnect the supply.

Plugs separated or access to junction boxes exposing live conductors and pilot circuit wired to incorrect outlet, not provided, defeated or not fail-safe.

Inadequate precautions taken to guard against induced voltages or capacitively coupled voltages from OHLs and lightning.

Indirect contact of personnel with a faulted cable

Failure of protection to detect and clear fault.

Poor procedural control for cable handling and practice.

Induced voltages from OHLs or lightning.

Pin holes in cable resulting in surface tracking.

High voltage onto low voltage pilot or control circuits due to inadequate phase segregation.

Use of cables that are not screened or provided with phase barriers to AS/NZS 2802.

Poorly designed earthing system including no provision of earth fault current limitation, faulted earth fault current limitation, faulted earth fault system or defective earth fault lockout device.

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Explosion of cable couplers or other uncontrolled release of energy

Poor design of cable accessories, e.g. not electrically symmetrical.

Poor maintenance of cable accessories resulting in ingress of moisture.

Poor management practice of cables and cable accessories, e.g. cable plugs and couplers left on the ground.

Damage of cable accessories resulting in degradation of insulation or phase barriers.

Poorly graded or incorrect setting of short-circuit protection.

Defective earth fault current limitation or earth fault current limitation not provided.

Defective earth fault protection or incorrect setting of earth fault protection.

No provision of phase barriers or phase barriers defective.

Over-tensioning of cable at coupler gland point (poor cable management practices).

Failure of the earthing system.

Partial discharge caused by poor design, aging, contamination or inclusion leading to insulation failure.

Reclosing (either manual or automatic) onto a faulted cable. (continued)

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TABLE 6.1 (continued) Typical risks Mechanical damage of trailing or reeling cable

Typical causes Faulty or poorly maintained reeling devices.

Poorly designed handling attachments.

Inadequate procedures.

Excessive tension.

Draglines swinging over its trailing cable and rocks falling from the bucket.

Material falling onto cable.

Machinery striking cables or running over cables.

Light vehicles, graders, dozers and other machinery running over cables.

Operation of cable within minimum bending radius.

Poor slinging and towing practices.

Abrasion of cable sheath from dragging over the ground.

Rear dump trucks driving through cable crossings with the rear dump tray (body) up.

Muscular skeletal damage

Manual handling of cables and accessories.

Coupling or de-coupling plugs.

Handling practices not established or not appropriate.

Health effects from materials Grinding, burning or other mechanisms for exposure of persons.

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Ignorance of the hazards and No hazard awareness training. risks Poor safety culture or Poor organizational leadership. attitude/Production demands Lack of procedures. overriding safety or environmental considerations Inadequate training.

6.4.3 Cable damage prevention Where trailing cables and reeling cables are moved by a machine, means shall be provided to prevent direct strain being placed on cable terminations. Movement of the cables shall be carried out in accordance with the manufacturer’s recommendations regarding the maximum tension, minimum temperature and bending radius.

All trailing cables and reeling cables shall be so located that damage by rocks, stones, etc., will be minimized. All trailing cables and drum cables shall be examined at regular intervals to ensure freedom of movement and freedom from damage.

Where the movement of trailing cables and reeling cables requires separation of cable couplers, the cable shall be isolated before the work is commenced.

NOTE: Equipment to separate and join plugs should be used.

6.5 INSTALLATION OF CABLES 6.5.1 Protection of cables Cables which may be subject to damage as a result of the movement of mobile plant (vehicles and mobile machinery) shall be conspicuously located or appropriately protected.

Such protection may take the form of— (a)

ramps and covers;

(b)

warning flags, markers or fences;

(c)

earth embankments;

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(d)

burying in pipes (with adequate air circulation) under defined roads;

(e)

overhead cable bridges; or

(f)

supporting cables above ground level.

Cable connecting plugs shall be laid at 90 degrees to the cable.

6.5.2 Maximum tensions to be applied to trailing cable 6.5.2.1 General All possible steps should be taken to ensure that recommended cable tensions are not exceeded.

The maximum safe working force (SWF) for flexible conductors in different applications is listed below in Table 6.2. Manufacturer’s datasheets should also be consulted.

TABLE 6.2 MAXIMUM CABLE TENSIONS Application Reeling

Trailing

Cable type

Maximum safe working force (SWF) N/mm 2

No sheath reinforcement

15

Sheath reinforcement

20

No sheath reinforcement

20

Sheath reinforcement

30

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NOTE: Maximum safe working force for metric flexible conductors when trailing is s = 20 N/mm 2 .

6.5.2.2 Calculating the maximum cable length to be pulled The maximum length of cable to be dragged or pulled from a suitably attached anchor point is calculated by the following equation:

L=

T

( f × W × 10)

where L

= maximum length to be pulled, in metres (m) NOTE: The cable loops should be half the maximum calculated value where they are to be straightened out.

T

= tension, in Newtons (N) − SWF × A where SWF = safe working force, in newtons per square millimetre (N/mm2).

A

f

= cable cross-section area of phase conductor, in square millimetre (mm 2)

= 0.5 (coefficient of friction of cable/surface) NOTE: This is a normally expected value specified by cable manufacturers, but does not take into account heavy terrain such as muddy conditions.

W

= mass of cable, in kilograms/metre (kg/m)

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6.5.2.3 Calculating the maximum cable length to be suspended Suspended unarmoured cables should not exceed the maximum pulling tension, as calculated by the following equation—

L=

T

(W × 9.8)

where L

= maximum length to be suspended, in metres (m)

T

= tension in Newtons (N)

9.8 = force of gravity W

= mass of cable, in kilograms/metres (kg/m)

6.5.3 Minimum bending radii of trailing cable The bending radius should be kept as large as possible and the minimum bending radius should always be maintained. Manufacturer’s datasheets should be consulted for specific data.

Examples of minimum bending radii are given in Table 6.3.

TABLE 6.3

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MINIMUM BENDING RADII OF CABLES (Figures quoted are multiples of the cable diameters) Application

Cables rated 1.1/1.1 kV

Cables rated 3.3 kV and above

Despatch drum barrel

6

8

Fixed bend

4

6

Free flexing

6

10

Repeated reeling

10

12

Passing over sheaves

10

15

NOTES: 1

Where reeling of cables involves directional changes or where the cable is subjected to an ‘S’ bend, the straight section of cable between the two adjacent bending points shall be not less than 20 times the cable outside diameter (OD).

2

Operationally, the term ‘bending diameter’ is often used (diameter = 2 × radius).

6.5.4 Cable roadways Trailing cables shall be installed on graded/prepared cable roads where practicable.

Cable roads shall be of sufficient width to allow for light and medium vehicle access for the entire length of the trailing cable.

Trailing cables shall be clearly identified to all persons working in the vicinity of the cable.

NOTE: Cable management plans should identify maximum spacing for trailing cable identification equipment for all foreseeable situations.

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6.5.5 Anchoring of cables Nylon webbing cable straps/stockings or fit-for-purpose cable handling grabs shall be used for anchoring trailing cables.

Nylon webbing cable straps shall be applied to a trailing cable and secured to avoid unravelling or strap movement on the cable.

NOTE: The manufacturer’s data sheets should be used for the recommended length of cable coverage.

Trailing cables shall be anchored to machinery in a manner that places no tension on the termination of the cable and minimizes stress on the cable due to the bending radius at the point of departure from the machine. The trailing cable shall be anchored at appropriate locations such as— (a)

cable plug joining stands;

(b)

flexible cable termination boxes (hot box);

(c)

cable tower bases;

(d)

cable gantry bases (in both directions of entry and exit from the gantry);

(e)

substation entry;

(f)

machinery;

(g)

any other point that may subject terminations to stress; or

(h)

any point at any equipment that creates a hazard from cable movement.

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6.5.6 Storage of cables Trailing cables shall be stored in a manner that prevents ingress of moisture or dirt to either cable terminals or plugs.

NOTE: Methods of storage include plug covers or cable bags.

Trailing cables shall be stored in such a manner as to allow access to both cable ends.

All trailing cables not in use and not intended for impending use shall be stored in a designated cable storage area.

Each designated cable storage area shall be well drained and shall be free from any debris or mining refuse.

Each trailing cable storage area should have restricted access to prevent unnecessary vehicular traffic at these locations.

6.5.7 Transporting of cables Trailing cables shall be transported by cable spools, cable boats or other means that minimize wearing and damage to the cables.

6.5.8 Snigging of cables The methods of attachment for snigging trailing cables shall be nylon webbed cable straps, aluminium cable clamps, or other suitably engineered devices that minimize crush force while minimizing slippage of the cable and cable machine attachment device.

NOTE: Nylon/hemp rope is not permitted to be used for snigging trailing cables.

When the loop is a ‘trailing loop’, the loop shall be monitored to ensure the loop does not get caught on an obstruction causing damage.

In wet weather, the length of cable permitted to be snigged may need to be reduced to reduce the load on the cable due to mud build-up.

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6.5.9 Cable towers and high wall gantries 6.5.9.1 General Where lifting, lowering or supporting cable or cable accessories, all lifting devices should be engineered and rated for the expected loads. Personnel utilizing such equipment should be adequately trained.

6.5.9.2 Cable towers Trailing cable towers shall be positioned to a maximum distance so as to allow a cable span that does not exceed the maximum tension allowed for the cable, attachment equipment and tower.

All cable towers and cable support equipment shall be designed and rated for the maximum span for the cables to be used.

All cables shall be securely anchored at the entry and exit of the cable tower span.

Cables shall be suitably supported at the top of the cable towers in a manner that minimizes stress on the cable due to the bending radius at the point of departure (e.g. specifically designed and rated polyurethane cable elbows or cable grabs).

NOTE: Cable elbows and cable grabs used for supporting cables should not be used for snigging cables.

Cable towers shall have the minimum clearance prominently displayed to oncoming traffic and have adequate clearance for any loaded or unloaded machine that passes under them.

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6.5.9.3 Cable gantries Where trailing cables pass over high wall/low wall, they shall be installed on high wall cable gantries or a chamfered edge that has no sharp objects that may damage the cable.

Highwall cable gantries shall have the cable anchored securely at the base in both entry and exit directions.

Highwall cable gantries shall be installed to keep the cable clear of the highwall face. No excess cable shall remain at the base of highwall.

6.5.10 Manual handling of cables The cable management system should be designed such that direct handling of energized high voltage trailing cables is, where practicable, eliminated.

NOTE: Direct handling of an energized high voltage cable is not recommended due to the possibility of being exposed to electrical energy.

Energized high voltage cable couplers shall not be manually handled.

Insulated lifting tongs, insulated hooks or straps, insulated work gloves and slings or other suitable equipment may be used to provide additional operator protection when handling energized high voltage cables.

NOTES: 1 These controls may not only help mitigate electrical hazards, but also assist in manual handling operations.

2 Where energized high voltage cables are to be handled, a risk assessment should be conducted to identify appropriate controls.

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6.5.11 Additional protection requirements for trailing cables Unprotected trailing cables shall not be driven over by any equipment. Machinery can drive over cables via adequately rated cable ramps or other means that maintain a clearance between the cable and machine.

Where tracked machinery are required to cross trailing cables, this may be achieved by placing trailing cables in an open trench allowing adequate distance between the machine tracks and the cable.

Trailing cables shall not be run out in such a position that they may be permanently buried by graded windrows, falls from the open cut highwalls or mining debris.

In the event that the trailing cable is covered with water, overburden, coal or debris, etc., the cable shall be cleared as soon as possible to prevent damage/overheating.

Due to derating factors, trailing cables shall be installed to maintain a minimum of 150 mm from any other cables along cable runs.

All trailing cable plug joins and joining boxes shall be located in a suitable position to enable safe access by personnel. Plug stands shall be used for all trailing cable plug joins.

Machinery operators shall not swing a loaded bucket over the trailing cable unless the cable is protected and special operator guidelines are adhered to.

Cables that are in close vicinity to a blast area shall be removed.

NOTE: Where there is a risk of damage from fly rock, the cable may be temporarily covered by material while in a de-energized state.

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De-energized cables shall not be laid parallel to OHLs due to the possibility of induced voltage.

Cables shall not be buried direct in the ground as overheating and damage can occur.

Where there is a risk of stored energy or risk of induced voltage, cables shall be discharged per high voltage procedures.

A method of reporting and recording cable damage shall be in place.

6.6 CABLE REPAIR Cable repairs shall be carried out in accordance with AS/NZS 1747.

6.7 PRECAUTIONS DURING LIGHTNING STORMS De-energized cables shall not be handled or repaired during lightning storms where there is a possible risk of direct strikes or from induced voltages.

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S E C T I O N

7

O V E R H E A D

AS/NZS 3007:2013

L I N E S

7.1 GENERAL Overhead lines (OHLs) (also known as powerlines) are one of the most significant sources of electrocution in Australia. OHLs are widely used in mining operations; they operate at LV and HV. OHLs at mines shall be designed to function properly and minimize the risk of direct contact by persons, machinery or equipment transported by machinery or personnel.

OHLs shall be designed and installed so as to ensure adequate mechanical strength, clearances and current-carrying capacity. Refer AS/NZS 7000.

Clearances may need to be increased above published values where operations associated with mining, treatment and transport (road and rail) take place near the overhead electricity line. Clearances shall be in accordance with Clauses 7.5.2 and 7.5.3.

An earthing conductor(s) shall be installed above the OHLs along their length to protect the OHLs from lightning strikes.

Signs should be installed at appropriate places to warn of the presence of OHLs. The signs shall state the voltage and the maximum height of any mobile plant (vehicles and mobile machinery) that can travel under the OHLs. The signs should be positioned so that workers have sufficient time to respond appropriately to the warning.

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NOTE: For guidance and information on safety signs for the occupational environment, see AS 1319.

Appropriate markers shall be installed— (a)

on OHLs crossing designated traffic routes to make them more conspicuous; or

(b)

where mine roads pass under OHLs by erecting height restrictions barriers.

NOTE: Mobile plant that have to pass beneath OHLs can be limited to a safe height.

NOTES: 1 The risk of contact with OHLs may be eliminated by using cables buried underground at transport crossings; however, this has to be balanced against the risks presented by these cables.

2 OHLs should be accessible for inspection purpose. In particular, access should be available at night and in poor weather.

For any work where the minimum safe clearances are encroached upon, power shall be removed from the OHL. NOTE: Power poles of wooden construction should not be used in areas where spontaneous combustion may occur.

7.2 EASEMENTS Not all OHLs on a mine site will be under the direct control of the mine. Transmission authorities and network service providers may have easements or own all or part of the OHL asset. Easements are required so that authorities can construct, reconstruct, operate and maintain their OHLs and to control activities under or near OHLs that may create an unsafe situation. Arrangements between the mine and the OHL owner will need to provide for safe access to and interaction with the OHLs and specify the types of mine controlled activity that can occur within the easements.

Easements shall be in accordance with AS/NZS 7000 and the operating agreements with the supply authority.

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Typical activities that are not permitted within an easement are— (a)

construction of buildings or other substantial structures;

(b)

the installation of fixed plant or equipment;

(c)

the storage of flammable materials or explosives;

(d)

vegetation with a mature height exceeding 4 m;

(e)

any obstruction placed within 15 m of an OHL structure or supporting ropes, wires or chains; and

(f)

parking of mobile plant with a height equal to or greater than 4.3 m.

Before carrying out any work near OHLs owned by a transmission authority or network service provider, their advice and permission needs to be sought, irrespective of any guidance given by this Standard.

7.3 MINE OWNED/OPERATED OHLS 7.3.1 Placement of OHLS

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In considering the requirements for OHLs the integrity of pole or tower structures (including stay wires) should not be compromised by mining or work practices. OHLs and their associated equipment should be placed so that normal mining operations can be carried out without affecting the safety integrity of the OHL. It is good mining practice to route OHLs— (a)

around or away from mine infrastructure (such as stockpiles, wash-down bays, workshops, hard stand areas, parking areas, maintenance areas and other work areas);

(b)

away from being directly above future underground mining areas likely to experience subsidence;

(c)

away from the mining area; and

(d)

to minimize crossing roads where large mobile plant such as dump/tipper trucks travel.

Where OHLs pass over such areas and, in particular, where mobile drilling, excavating, loading, hauling or lifting equipment is used in normal mining operations, conductors should be placed so that the clearances specified in Clause 7.5 are always maintained between the conductors and the mobile plant, any of its extensions, people on the equipment or items with which they may be in contact.

NOTE: Bump safe covered conductor overhead wire systems have been developed for voltages up to 66 kV; the use of these systems should be considered.

When determining this clearance, account shall be taken of conditions which give the least clearance between the OHL and mobile plant (e.g. maximum sag of OHL conductors).

7.3.2 Other design considerations Apart from compliance with design codes, the mine operators should consider insulation coordination of the OHL and equipment (refer AS 1824 series).

It may be necessary— (a)

to install additional earthing at poles and towers to reduce step and touch voltages to acceptable levels; or

(b)

to prevent access to poles and towers where excessive touch and step voltages exist.

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OHL design should take into consideration the impact of mine subsidence. OHLs should be designed to withstand the effects of the predicted mine subsidence. Consideration should be given to placing the OHL support structures outside of the extracted area of longwall blocks. Where this is not possible, a subsidence monitoring program should be implemented to detect excessive OHL and OHL structure movement.

NOTE: OHLs have been successfully installed and withstood up to 2 m subsidence.

For electricity supplies to underground mines overhead earth wires should be installed (see AS/NZS 1768) and surge diverters should be installed at the termination of OHLs. Surge diverters should be installed at every point of transition from OHL to cable.

The type of material that the OHL is to be stood in should be taken into consideration, e.g. if the OHL is in sand, then the sand may erode from a pole, or build up under a OHL, thereby reducing the height of the OHL. 7.4 OHL CORRIDORS AND WORK NEAR OHLS OHL corridors should be established with access controlled by an access permit system.

The corridor should extend a sufficient distance from the extremities of the OHL so that direct contact or flashover is prevented under normal operating or foreseeable abnormal circumstances.

NOTES: 1 It is accepted practice that a 10 m corridor is to be applied from the base of the pole.

2 For mobile plant movement clearances, refer to Clause 7.5.

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Figures 7.1 and 7.2 may be used to establish the dimensions of OHL corridors.

NOTES: 1 Storing of equipment, product, waste and the like should be prohibited within the corridor.

2 The use of any digging or lifting machinery within the corridor should be prohibited in all but exceptional circumstances; however, when work has to proceed under or near OHLs, particularly with heavy mining equipment or earthmoving equipment or cranes, it is essential to stay clear of OHLs using the ‘No Go Zone’ principles. For OHLs on poles, the ‘No Go Zone’ is anywhere above the OHL and within 3 m each side of and 3 m underneath the OHL (refer Figure 7.1).

Provided a safety observer is present at all times, work may be carried out between the edge of the ‘No Go Zone’ and the following clearance within each side of and underneath the OHL: (a)

6.4 m for OHLs on poles and towers up to 33 kV (see Figure 7.1).

(b)

10 m for OHLs on poles and towers above 33 kV (see Figure 7.2).

NOTES: 1 Figures 7.1 and 7.2 are derived from Significant incident Report No. 2/2007, Department of Primary Industries, Victoria.

2 It may be the case that high transmission voltages (e.g. 132 kV and above) may be present on single pole structures, in which case the danger of this higher voltage level has to be taken into consideration.

For OHLs on towers, the ‘No Go Zone’ is anywhere above the OHL, 8 m of each side of the OHL, and 8 m underneath the OHL (refer Figure 7.2).

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NO GO ZONE A ny w h e r e a b ove p owe r l i n e and wi thi n 3 m e a c h s i d e and 3 m f r o m th e b ot to m Open area outside 6.4m of p owe r li n e s

S p ot te r required b e t we e n 3 - 6.4 m of p owe r li n e s

S p ot te r required b e t we e n 3 - 6.4 m of p owe r li n e s

Open area outside 6.4m of p owe r li n e s

3m

3m

3m

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FIGURE 7.1 OVERHEAD POWERLINES ON POLES ON TOWERS (NOMINAL MAXIMUM VOLTAGE 33 kV)

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NO GO ZONE

Open area outside 10 m of p owe r li n e s

S p ot te r required b e t we e n 8 -10 m of p owe r li n e s

A ny w h e r e a b ove p owe r l i n e and wi thi n 3 m e a c h s i d e and 8 m f r o m th e b ot to m

8m

S p ot te r required b e t we e n 8 -10 m of p owe r li n e s

Open area outside 10 m of p owe r li n e s

8m

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8m

FIGURE 7.2 OVERHEAD POWERLINES ON POLES AND TOWERS (NOMINAL VOLTAGE >33 kV)

7.5 CLEARANCE TO MOBILE PLANT 7.5.1 Risk assessment The risk of contacting OHLs by mobile plant brought to site (newly purchased, hired or belonging to contractors) shall be assessed. Before mobile plant that is not regularly used is used on the site, the likelihood of the clearance between the mobile plant and the OHL being reduced below specified requirements shall be determined.

Initially the likely clearances shall be determined by comparing the known minimum ground clearances of OHLs on the site with the maximum height above the ground of the mobile plant, its load, any item of the equipment extended to its full height, or persons on the equipment.

If this comparison shows that the specified clearances can always be maintained, the equipment may be used without restrictions, provided the road surface is not increased in height due to ballast, grading, etc.

Should the initial determination show that the clearances specified cannot always be maintained, a thorough inspection of the route to be taken and the work to be carried out on the site should be made. That inspection should determine clearances between the mobile plant and the OHL. This should be determined by physically checking the height of the mobile plant and the ground clearance of the OHL with suitable measuring devices.

The areas of the mine that cranes and other mobile plant are required to access shall be defined and delineated by using warning signs, rigid protective barriers or tape protective barriers with high visibility ‘bunting’ or similar material.

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The permissible routes for mobile plant shall be defined in order to minimize the risk of contact with OHLs. In particular, the location and voltage of all OHLs at the site shall be known before operating or working with any crane. Many accidents arise when operators deviate from established routes.

Should the site inspection show that the clearances specified may not be maintained the OHL should be isolated, short-circuited and earthed whilst the mobile plant is in use near the OHL. Should the site inspection show that movement of the mobile plant could cause damage to the OHL, the OHL should be disconnected and removed from the area where the mobile plant is to be used.

7.5.2 Vertical clearances

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The minimum clearances specified in Table 7.1 shall be observed when mobile plant passes under OHLs. The clearances apply from the highest point of the mobile plant to the OHLs. NOTES: 1 Minimum clearance is the difference between the lowest height of the overhead conductor and the highest point of the mobile plant.

2 Ground clearance is the perpendicular distance between the ground and the conductor. That distance is the smallest arc which can be drawn from the conductor, the ground being tangent to it.

3 The condition which gives the maximum distance above the ground of the equipment will need to be taken into consideration. For example, in the case of a dump truck, this would be when the body is fully raised and springs and tyres are at maximum extension (after a bump); and in the case of a drilling rig, its mast is in the vertical position.

For mobile plant with a long overhang (such as the jib of a mobile crane) the ground clearance to be considered may need to be when the mobile plant (with jib down) is passing over the crest of a hill causing the overhanging part to have a greater clearance to the ground than if the ground was level.

Rear dump trucks and other mobile plant that can raise parts above their normal level commonly contact OHLs and overhead cables even when warnings about the dangers of raising the part (e.g. the tray) are fitted in the operator’s cabin.

4 Other considerations include— (a) the maximum pond level where floating plant is used, which may be due to the raising of the water table, pump failure or flooding; (b) the effect of swinging conductors sag; and (c) the maximum expected wind speed.

Provided OHLs are installed and maintained with clearances to mobile plant as specified in this Standard, the equipment to which these clearances relate may be used without restrictions.

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TABLE 7.1 MINIMUM CLEARANCES FOR THE MOVEMENT OF VEHICLES AND MACHINERY UNDER AND IN THE VICINITY OF OHLS Nominal voltages (phase-to-phase) kV, r.m.s

Minimum clearance*†, mm

≤1.1

1000

>1.1 ≤33

2300

>33 ≤66

2500

>66 ≤110

3000

>110 ≤220

4000

*

The minimum clearances specified take into account the fact that the system voltage may vary by up to 10% from the nominal voltage.

†

Allowance should be made for the possible sag and swing of the OHL.

7.5.3 Horizontal clearances

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Where mobile plant is operated in the vicinity of OHLs and the height of the mobile plant is such that the minimum vertical clearances specified in Table 7.1 cannot be achieved, an adequate horizontal clearance of not less than the appropriate value specified in Table 7.1 shall be maintained between the mobile plant and the OHL provided the design of the road prevents encroachment by the mobile plant or the mobile plant is adequately controlled.

NOTE: An OHL installed adjacent to a road which provides adequate horizontal clearance is a circumstance where the movement of the mobile plant is considered to be in control.

7.6 CLEARANCES TO HAND-HELD OBJECTS Where OHLs pass over areas where long conducting objects may be handled as part of the normal mining operations, e.g. metal survey staffs or pipes for the pumping system, the overhead conductors should be placed so that the clearances specified in AS/NZS 7000 are maintained. When manually carried, pipes and long metallic objects should be carried in the horizontal position by at least two people.

All factors should be taken into account to determine the least clearance between the handheld object and the OHL, e.g. maximum sag condition to be considered and, in the case of a survey staff, this would be the staff fully extended and held perpendicular to the ground surface at a height of 2.4 m above the ground.

7.7 CLEARANCE TO EXCAVATIONS OHLs shall be placed at such a distance from excavations that the stability of any pole, tower, associated stay lines, earthing conductors and earth electrodes are not affected by the excavation or slump.

7.8 CLEARANCE TO BLASTING OPERATIONS OHLs shall be placed so that fly rock from blasting operations will not damage any part of the OHL. The OHLs should be able to withstand overpressure waves caused by blasting.

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Electric blasting considerations include the following: (a)

Induced effects in electric blasting circuits. Stray currents can be induced in the shot firing cables during fault conditions on the OHL or in normal operation in the case of single wire earth return (SWER) OHLs.

(b)

The possibility of OHLs falling to the ground.

NOTES: 1 Electrically initiated explosive devices and connecting cables should not be used in the vicinity of OHLs. 2 For further information refer to AS 2187.2.

7.9 CLEARANCE TO STOCKPILE AND TAILING AREAS OHLs shall be kept well clear of stockpiles and tailing areas.

NOTE: The clearance should be such that stockpiles and tailings cannot encroach on the OHLs in such a manner that safety clearances will be compromised. The stockpile should not encroach into the OHL corridor.

7.10 CLEARANCE TO STORAGE AREAS OHLs shall be kept well clear of storage areas.

NOTE: The clearance should be such that stored equipment and mechanical lifting devices used for storing equipment cannot encroach on the OHLs in such a manner that safety clearances will be compromised.

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7.11 CLEARANCE TO STRUCTURES AND PEOPLE TRANSIT AREAS OHLs shall be kept well clear of structures not associated with the OHL and areas where people regularly transit (e.g. car parks, muster areas).

7.12 REDUCTION OF CLEARANCES Particular care shall be taken to ensure that the clearance of OHLs to ground is not reduced below the minimum values permitted by dumping or tipping of material, grading of roadways, landscaping, or by creating storage areas, or by the positioning of buildings or structures.

7.13 MOVING OF OHLS Before moving an OHL, all conductors shall be isolated and made safe from inadvertent reconnection and the effects of induction and capacitive coupling.

When persons are working at heights, appropriate precautions shall be taken to minimize the risk of falling (e.g. use of EWPs and safety belts).

Precautions shall be taken to ensure that all poles or towers are structurally sound and that releasing the conductors will not cause instability to other sections of the OHL. All mobile plants shall be prevented from passing under or over an OHL during dismantling and erection unless appropriate protective measures are taken.

Unused poles shall be removed. Before poles or associated hardware are re-used, an inspection of the poles, hardware and conductors shall take place to ensure they are suitable to be returned to service. When poles are re-used, the installation shall comply with AS/NZS 7000.

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7.14 PRECAUTIONS DURING LIGHTNING STORMS De-energized OHLs shall not be handled or repaired during lightning storms where there is a possible hazard from direct strikes or from induced voltages.

In the event of an electrical storm in the area of the OHL, all work on the OHL shall cease.

NOTES: 1 This should be part of the management plan dealing with the risks from lightning.

2 It may be necessary to cease work when lightning activity is a substantial distance from the work area as the OHL may traverse to/from the lightning activity.

7.15 OPERATIONS INVOLVING LONG METALLIC STRUCTURES Care shall be taken when long metallic structures (e.g. moveable conveyors, pipeline systems) are run parallel to OHLs because of possible hazards from induced voltages.

NOTE: For the principles that apply to hazards on metallic structures see AS/NZS 4853.

7.16 CLEARING VEGETATION NEAR OHLS ENA Doc 023 gives details of the work that should to be carried out.

7.17 MINE SITE INFORMATION ON OHLS

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Information should be readily available to mine staff to facilitate risk assessments and controls related to operations near to OHLs. The information should identify the following: (a)

The geographical location of all OHLs on the mine property.

(b)

The location of every power pole/tower.

(c)

The pole/tower construction (timber, concrete, steel).

(d)

Insulated or uninsulated conductors.

(e)

The nominal voltage.

(f)

Overhead earth wires and surge diverters.

(g)

The OHL owner (e.g. mine, transmission authority, network service provider).

(h)

Any associated easements.

(i)

Whether the OHL is for mining purposes.

(j)

The location of all isolation points.

(k)

The minimum height of the OHL over roadways.

(l)

Delineate power corridors.

(m)

Pole inspection records.

This information necessitates mine plans, distribution diagrams and associated registers being readily available and the plans to be on display at operational supervisors offices and ‘muster areas’.

7.18 EMERGENCY RESPONSE PLAN FOR CONTACT WITH OHLS A risk assessment shall be undertaken covering foreseeable emergency situations that might result from mobile plant contacting OHLs, including the following: (a)

Contact with OHLs when the power trips.

(b)

Contact with OHLs when the power does not trip.

(c)

A fire starting on the mobile plant.

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(d)

A grass or bushfire starting.

(e)

A tyre catching fire and/or tyre pyrolysis leading to a tyre explosion.

(f)

A combination of Items (a) to (e).

From these risk assessments, an OHL emergency response plan shall be developed and integrated in the mine’s emergency management plan, including firefighting equipment requirements, liaison with power supply authority and owners of OHLs, liaison with outside emergency agencies, electrical shock victim management and electrical burns management.

7.19 EMERGENCY ACTION IF THERE IS AN ACCIDENT

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Should contact be made with a live OHL or a flash-over occur between a live OHL and a crane or other item of mobile plant, the following actions should be taken: (a)

Stop all work in the vicinity of the incident and summon help to have the OHL isolated.

(b)

Never touch an OHL—even if it has been brought down by machinery, or has fallen.

Be aware that any fallen conductors could also whip around unexpectedly.

(c)

Never assume OHLs are dead.

(d)

When a machine is in contact with an OHL, electrocution is possible if anyone touches both the machine and the ground. Stay in the machine and lower any raised parts in contact or drive the machine out of the OHLs if you can.

(e)

Be aware that the rubber tyres of mobile plant subjected to contact with OHLs may explode by pyrolysis effect, causing serious injuries.

(f)

After de-energization of the OHL, an exclusion zone of 300 m should be maintained around rubber-tyred mobile plant for at least 24 hours after contact. This is to ensure that no-one is put at risk in the event of a tyre explosion.

(g)

If non-rubber tyred mobile plant contacts an OHL, isolate the mobile plant for at least 24 hours until all possible sources of explosion (hydraulic cylinders and tanks) are neutralized.

(h)

When a crane or other item of mobile plant has been in contact with a live OHL, it should be checked by a competent person for damage. Any actions recommended by the competent person should be completed before the mobile plant is returned to service.

(i)

If you need to get out to summon help or because of fire, jump out as far as you can without falling over or touching any wires or the machine—keep upright and jump away keeping both feet together.

(j)

Request the electricity company to disconnect the supply to transmission networks.

Even if the OHL appears dead, do not touch it; automatic switching may reconnect the power.

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P O W E R

S U P P L I E S

8.1 POWER SUPPLIES FROM MOBILE MACHINERY For off-board mobile and moveable auxiliary equipment (e.g. welding equipment, vulcanizing transformers) which require the provision of a protective conductor, either the protective conductor shall be visible throughout its length or one or more of the following measures shall be adopted: (a)

The protective conductor shall be monitored for increase in resistance.

(b)

Sensitive earth leakage protection shall be provided.

(c)

A visible equipotential bonding conductor shall be provided between the off-board mobile or moveable auxiliary equipment and the plant from which it is supplied.

8.2 SELF-CONTAINED POWER SYSTEMS When the supply of electrical energy is self-contained within stationary, mobile, or moveable items of equipment and there is no external supply, such equipment need not be connected to the general mass of the earth.

8.3 WELDING MACHINES AND EQUIPMENT

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Welding machines and equipment shall be constructed to achieve safety outcomes identified in AS 60974.1 and AS 60974.6 as applicable and comply with AS 1674.2.

All welding machines shall be fitted with a hazard-reducing device as defined by AS 1674.2.

NOTE: For welding machines a means of isolation, as specified in Clause 2.9, is not required if power to the welding machine is supplied through a switched plug and receptacle.

8.4 INVERTERS AND UNINTERRUPTABLE POWER SUPPLIES 8.4.1 General AS/NZS 3000 details requirements for inverters and uninterruptable power supplies (UPS) relating to— (a)

control;

(b)

isolation;

(c)

overcurrent protection;

(d)

earthing;

(e)

neutral continuity; and

(f)

electrical equipment connected to the output.

The manufacturer’s instructions should be followed for the safe use of inverters and UPSs. 8.4.2 Inverters Portable inverters shall comply with the requirements of AS/NZS 4763.

Stand-alone inverters shall comply with the requirements of AS/NZS 5603.

Grid connected inverters shall comply with the requirements of the AS 4777 series.

NOTE: Mine sites should comply with the requirements for the safe use of inverters as per AS/NZS 3012.

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8.4.3 Uninterruptible power supplies Uninterruptible Power Supplies (UPS) shall be used in accordance with AS 62040 (series).

8.5 RELOCATABLE BUILDINGS AND IT EARTHING SYSTEMS 8.5.1 General Relocatable buildings form an integral part of an electrical installation on mine and quarry sites. These buildings are usually pre-wired to comply with AS/NZS 3000 and AS/NZS 3001, based on a TN earth system (MEN) and arrive on site in a ready to connect state, and are generally used for offices or as an ablution facility. The ablution facility may be a high-risk area due to high humidity, water and dampness and may require additional considerations to reduce the risk from electric shock.

Where relocatable buildings designed for use on a TN system are to be connected to an IT system, the neutral for the relocatable building shall not be derived from the neutral point of the IT system.

NOTE: See Paragraph A5.6, Appendix A, for an explanation of the issues involved.

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An isolation transformer shall be installed between the IT supply and the relocatable building. The isolation transformer options are as follows: (a)

415/240 V 3 phases IT connected isolation transformer. This increases the protection against electric shock, as the phase-to-earth voltage is now 139 V. If this option is selected the special requirements identified in Clause 8.5.2 shall be implemented with regard to the switches and outlets installed in the relocatable building.

(b)

415/240 V 2 phases IT (via centre tap on the 240 V winding) connected isolation transformer. This increases the protection against electric shock, as the phase-to-earth voltage is now 120 V. If this option is selected the special requirements identified in Clause 8.5.2 shall be implemented with regard to the switches and outlets installed in the relocatable building.

(c)

415/240 V 2 phases TN (one phase of the 240 V winding is earthed) connected isolation transformer.

8.5.2 Isolation switches If the 240 V supply is an IT system all conductors shall be considered as active and shall be switched in accordance with AS/NZS 3000. This includes isolation switches for air conditioners, hot water services, lighting services, etc.

8.5.3 Earth fault protection testing In accordance with AS/NZS 3000, testing of Residual Current Devices (RCDs) shall be undertaken upon completion of the installation. Routine testing of RCDs should be performed and, as such, consideration should be given to the addition of a testing outlet for each of the circuits fitted with a RCD. This testing outlet provides for ease of testing and lowering the risk of exposure to open switchboards whilst testing. This testing outlet should be switch selectable from each circuit, thus simplifying the testing on circuits that do not have a suitable socket outlet (e.g. a lighting circuit).

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SECTI ON 9 ELECTRIC ITY SUPPL Y TO S A F E T Y C R I T I C A L M I N E I N F R A S T R UC T U R E F O R U N D E R GR O U N D M I N E S * 9.1 SAFETY CRITICAL ELECTRICAL SYSTEMS 9.1.1 General Safety critical electrical systems are those systems which supply safety critical infrastructure (plant or equipment).

9.1.2 Safety critical infrastructure Safety critical infrastructure falls into the following two categories: (a)

That whose failure could lead to immediate risk to the safety or health of any person.

(b)

That whose failure might prejudice the recovery of an emergency situation or the conduct of rescue operations.

9.1.3 Examples of safety critical infrastructure

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Systems affecting the safety or health of persons include the following: (a)

Powered winding systems.

(b)

Ventilation equipment where the interruption of ventilation would lead to a build-up of gases to hazardous concentrations.

(c)

Firedamp drainage equipment where failure could lead to the build-up of flammable gases.

(d)

Pumping equipment where failure may lead to flooding, which impedes the safe exit of persons from the mine.

(e)

Systems affecting emergency situations or rescue operations (e.g. communications systems and gas-monitoring systems) necessary to facilitate— (i)

the safe evacuation of a mine, or parts of it;

(ii)

the recovery of an emergency situation;

(iii) the control of rescue operations; and (iv)

environmental monitoring systems which supply information on the state of the mine atmosphere or equipment.

Not all mines will have the full range of safety critical infrastructure. Some mines will have very little, and some none at all. What is safety critical at a particular mine depends on the hazards present and the risks that they pose to persons.

9.1.4 Risk assessment To establish the infrastructure, all possible dangerous situations, where the continuity and reliability of the power supply is needed for safety reasons, shall be dealt with and managed in an effective manner. A risk assessment shall be carried out to consider all potential mining hazards and the likely consequences from a loss of power to associated ancillary equipment or services such as— (a) *

shaft side equipment and shaft signals needed for mine winders to operate; Section 9 contains UK public sector information, being based on the UK Health and Safety Executive publication Guidance on the design and construction of safety critical electrical systems at mines, 2001.

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(b)

transducers providing signals to safety critical equipment;

(c)

data communications systems used to monitor safety critical equipment or the underground environment;

(d)

firefighting pumps;

(e)

medical equipment in medical centres; and

(f)

communications centres, lamp rooms, and emergency organization rooms or other areas identified by risk assessment.

The assessment should also take account of any measures necessary to prevent one item of faulty equipment causing damage to other safety critical equipment. Such measures might include— (i)

fire barrier wall designed to withstand impact and blast forces between sections of switchgear to prevent a chain reaction of failures if one item of plant suffers a catastrophic failure;

(ii)

suitable fire-resistant walls, doors and cable routes to prevent fire spreading and damaging safety critical equipment;

(iii) firefighting equipment and arrangements to tackle electrical fires; and (iv)

reducing the fire loading by minimizing the use of equipment filled with large quantities of flammable oil, in places where there is a lot of safety critical equipment (such as winding engine houses and main ventilating fan houses).

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9.2 CONTINUITY OF THE ELECTRICAL SUPPLY TO THE MINE 9.2.1 Integrity, reliability and security of the supply to the mine A minimum of two independent reliable electrical supplies are recommended at mines— (a)

where ingress and egress is only possible through shafts; and

(b)

with safety critical ventilation systems.

Where there are two independent electrical supplies, each supply shall be secure and capable of maintaining power to— (i)

the winding engines;

(ii)

the main fan(s); and

(iii) other safety critical infrastructure.

9.2.2 Severe weather conditions Precautionary measures shall be taken when severe weather conditions are likely to cause disruption of the main power supplies to the mine. Where provided, a check shall be undertaken to ensure— (a)

the mine’s standby feed and first aid rooms feed are available; and

(b)

mobile generators have sufficient fuel.

9.3 CONTINUITY OF SUPPLY TO THE UNDERGROUND CONTAINING SAFETY CRITICAL INFRASTRUCTURE

WORKINGS

9.3.1 Design of networks and selection and maintenance of equipment 9.3.1.1 Distribution network design Distribution networks used to supply safety critical infrastructure should be designed to minimize disruption of the electrical system during testing, examination, inspection, maintenance or alteration.

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The distribution network design should be based on the following: (a)

When selecting equipment to supply or monitor safety critical infrastructure, avoid that which is known to be susceptible to failure.

(b)

Try to ensure that all safety critical plant can be supplied and operated at full capacity in the event of a single line component failure.

(c)

Where possible, main underground substations should be supplied from the surface by at least two cables which form a ring, duplicates or parallel feed system. As far as possible, route each cable through different shafts, or drifts, and roadways to minimize the possibility of a single hazard (e.g. roof fall) affecting both cables.

(d)

Ring main systems are not usually appropriate for supplying electrical power to safety critical infrastructure. It is difficult to set protection, and the whole ring can be tripped by a single fault on the system.

(e)

Where distribution is by parallel feeders, arrange the system so that— (i)

each feeder is operated as an independent system whenever possible;

(ii)

directional protection is provided;

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(iii) each feeder is designed with sufficient capacity to supply all safety critical plant; (iv)

the system is designed to allow switching between feeders to be carried out without interrupting the supply to the mine; and

(v)

the phase rotation and instantaneous voltage are correct.

For duplicate feeders operated from a common supply point, directional relay protection should be provided.

9.3.1.2 Protecting circuits Circuits supplying safety critical infrastructure should be segregated to avoid sympathetic tripping due to non-related faults on the system. Circuit protection should be arranged to discriminate between real and non-related faults.

9.3.1.3 Sustaining network supplies in the event of disruption When assessing the protection necessary to guard against the unintended loss of power supplies to safety critical infrastructure, and those measures that are required to ensure that power can be quickly restored after an interruption, the following should be considered: (a)

Whether the risk of unintentional tripping by using tripping mechanisms with a low susceptibility to system disturbances can be minimized.

(b)

Whether the likelihood of spurious tripping by removal of unnecessary protection circuits can be reduced.

(c)

The use of shunt tripping systems specifically designed to be highly reliable instead of under-voltage tripping, provided that there is no increase in risk from unintended operation of equipment or failure to trip of electrical protection.

(d)

The use of circuit-breakers which can be reclosed— (i)

automatically; or

(ii)

from a remote position (e.g. from the mine control room), to minimize the length of power supply interruptions.

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9.3.1.4 Cable, cable couplers To prevent mechanical damage, all cables supplying safety critical infrastructure shall be of the steel wire armoured type.

NOTE: Where there is a foreseeable risk of mechanical damage, cables for telephones and intrinsically safe circuits to and from underground workings should also be of the steel wire armoured type.

All cables shall be— (a)

routed to minimize the chance of damage;

(b)

properly terminated; and

(c)

properly supported.

NOTE: To reduce the number of potential failure points, try to reduce the number of cable couplers that use ‘pin and socket’ type connections.

9.4 CONTINUITY OF SAFETY VENTILATION EQUIPMENT

CRITICAL,

ELECTRICALLY

POWERED

9.4.1 Provision of ventilation equipment The main and standby electricity supplies shall be sufficiently secure to give a high degree of assurance that the main fan(s) will run continuously. What is provided to secure supplies will depend on the hazards present and the risks they pose if power to the main fan is lost.

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The hazards that might result from a main fan stoppage include— (a)

flammable gases in dangerous concentrations, including the risks posed by degassing operations;

(b)

high concentrations of toxic or suffocating gases;

(c)

lack of oxygen; and

(d)

excessive temperatures/humidity.

The greater the hazards and risks, the more secure power supplies should be.

Clauses 9.4.2, 9.4.3, 9.5 and 9.6 give provisions on electrically driven surface fans and booster fans, which will apply depending on the circumstances at a particular mine.

9.4.2 Surface fans If a continuously running surface fan is needed to maintain a safe mine atmosphere, a standby fan is strongly recommended. A standby fan will ensure the continuity of ventilation if the main fan breaks down.

Where there are both main and standby fans, if possible, there should be a separate power supply to each of them. This will greatly reduce the chance of a total loss of supply due to a single cause and therefore increase the likelihood that one fan can be run.

A separate power supply should be provided by— (a)

using different distribution boards and separate buildings for housing the equipment;

(b)

splitting a single distribution into two with a bus section switch between them; and

(c)

providing another power supply source, e.g. diesel generator.

Ideally the standby fan should have the same capacity as the main fan. Both the main fan and the standby fan should be used as the duty fan at suitable intervals to ensure the reliability of both.

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Where a fan is sited in a remote location and is unattended, provision of automatic or remote restarting should be considered, particularly if conditions in the mine could rapidly deteriorate in event of a stoppage.

Where the required amount of ventilation is provided by multiple fans, consideration should be given to designing the system so that in the event of one fan failing the capacity of the remaining fans can be increased to meet the demand.

Where fan-monitoring circuits are provided (e.g. for vibration or temperature), they should be set to give warning rather than to trip the fan so that corrective action may be initiated.

The fan should only trip when the monitoring indicates that there is a risk of severe damage to the fan or some other danger (e.g. causing a fire in the roadway).

To reduce the potential for serious damage, the main circuit-breaker electrical protection circuits should be set up to remove power as quickly as possible under electrical power fault conditions. At the same time care should be taken that electrical protection circuits do not spuriously trip surface fans in the event of transient supply disturbances.

‘Fan-running’ and ‘fan-stopped’ indicators may provide additional safety and efficiency benefits. If they are provided, they should be sited at places where they can be seen by persons who can take action or initiate remedial action.

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9.4.3 Provision of a dedicated feeder system for booster fans The reliability of underground booster fans can be greatly improved by providing a dedicated feeder system, as this reduces the risk of power loss due to faults on other non-safety critical equipment. It is better for the dedicated supply to start at the mine surface and include its own dedicated shaft or drift feeder. Providing the means to connect onto a standby supply may also prove useful in the event of a major failure in the normal dedicated booster fan supply.

9.4.4 Surface restarting and automatic restarting of booster fans Restarting booster fans automatically or from the surface can significantly improve the reliability of a mine’s ventilation system. Such facilities make it possible to re-establish ventilation quickly once power is restored.

9.5 MONITORING AND CONTROL Control equipment shall be arranged to prevent any fan restarting if— (a)

the firedamp concentrations in the general body of air at the fan installation exceeds the prescribed limit;

(b)

any of the electrical equipment has tripped because of electrical power fault;

(c)

conditions such as short-circuit, earth fault or overload are present; or

(d)

any other main ventilating machinery needs restarting beforehand.

Other protective equipment, such as— (i)

vibration monitoring;

(ii)

water curtain; and

(iii) emergency stop switches, should be arranged to minimize the chance of them leading to an unnecessary fan stoppage.

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9.6 POWERED WINDING SYSTEMS 9.6.1 Availability of exits from the mine The power supplies to each winding system should be as secure as practicable.

Where the only two means of escape are by separate winders, each winder shall have separate power supplies. This ensures that no single failure will adversely affect the operation of both systems.

Alternatively another supply source, e.g. from a standby generator, may provide the required security.

It should also be ensured that certain ‘associated parts’ of the winder and shaft side equipment can be operated if the main power supply to the mine is lost (for example, shaft side interlocks, shaft signals, and communications).

Where safety-related winding functions rely on a compressed air supply an alternative supply of compressed air, for example from an emergency air compressor, should be available.

When for some reason a wind has not been completed and people are held in the shaft for prolonged periods, in-cage communication systems can reduce stress and assist their safe recovery. Power supply to such equipment should be kept in serviceable condition.

9.6.2 Facilities to cater for breakdown of powered winding systems

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As part of the emergency resources and preparedness required, the underground mines shall provide suitable and effective auxiliary apparatus and equipment to enable persons to gain exit to the surface safely in the event of a breakdown of the normal winding systems.

Foreseeable circumstances when the normal winding apparatus might not be available include— (a)

a widespread power failure to such an extent that it becomes necessary to evacuate persons from the workings;

(b)

a breakdown of the winding apparatus, which makes it necessary to complete the wind using an alternative means to the main winding apparatus;

(c)

a hold-fast or immobilization of a conveyance in the shaft; and

(d)

the need for persons working or travelling in the mine shaft to leave in an emergency.

Some of the recognized methods of providing the required auxiliary facilities are— (i)

gravity winding apparatus;

(ii)

an independent ‘pony motor/engine’ driving the main drum;

(iii) mobile emergency winder; (iv)

any standby power supply necessary to operate equipment such as shaft signals and shaft-side interlocking systems; and

(v)

auxiliary ‘pony’ drive.

In the case of auxiliary ‘pony’ drives, it should be ensured that— (A)

its source of power is independent of the power source to the winding engine; and

(B)

it is capable of driving the main drum or rope sheave in the worst case out-of-balance condition.

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9.6.3 Gravity winding Gravity winding usually involves placing water tanks on the uppermost conveyance to increase its weight. The out-of-balance load is used to raise the lower conveyance in a controlled manner. Even though the winder requires no electrical power to move, a power supply may still be needed for— (a)

the winder’s hydraulic or pneumatic brakes;

(b)

certain winder controls including safety circuits;

(c)

water pumps to get water to the gravity winding tanks;

(d)

communications; and

(e)

shaft signals.

9.6.4 Testing of auxiliary pony drive and gravity winding systems Both the gravity winding and pony-drive facilities need periodic checking and frequent operation to ensure that they are available and ready for use when needed. Ideally, there should be a full mock test at least every 12 months.

Such tests present an opportunity for training new staff and re-training existing staff in the procedures required by site emergency preparedness strategies.

9.6.5 Diesel-driven emergency generators

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A diesel-driven emergency generator can provide a power source which can be connected onto the appropriate distribution board(s).

At mines with a.c. winders and dynamic braking, a higher-power emergency generator that is capable of operating the winder’s dynamic braking circuit shall be selected. This will give better speed control of the conveyances during gravity winding and removes the need to depend totally on the winding engine’s mechanical brakes. Where the generator does not have sufficient power to enable dynamic braking, the need to provide additional cooling for the brake paths should be considered.

9.7 POWER SUPPLIES TO DE-WATERING AND FIREDAMP DRAINAGE PLANT AND EQUIPMENT Where there is a risk of water or firedamp entering the mine, and drainage systems have been provided as part of the control measures, steps similar to those described for ventilating fans and winding engines may be needed to ensure continuity of the power supply to the drainage equipment and its associated instrumentation and monitoring.

For mines with complex underground workings interconnected by automatic telephones or other means of electronic communication, consideration should be given to installing a ‘telephone emergency desk’. Such a desk should— (a)

be able to be manned in an emergency;

(b)

have routed through it all of the important telephone lines;

(c)

have a facility to override an existing conversation on an engaged automatic line; and

(d)

prevent unwanted calls to a specific telephone(s), usually at the incident site.

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1 0

T R A N S P O R T SYSTE MS

C O N V E Y O R

10.1 GENERAL This Section specifies the requirements for electrical equipment of transport conveyor systems.

Transport conveyor systems are moveable or stationary mechanical items of plant designed for the conveying of materials continuously from one location to another (e.g. belt conveyors, chain conveyors, bucket conveyors, paddle or scraper conveyors, screw conveyors, hydraulic or pneumatic conveyor systems.

Transport conveyor systems shall comply with the requirements of AS 60204.1, AS 60204.11 and AS 1755.

10.2 CONVEYOR CONTROLLERS

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In addition to the requirements of AS 1755, conveyor controllers shall comply with the following: (a)

The controller design shall incorporate a single point of isolation (i.e. main isolator).

This main isolator shall be located in its own compartment and comply with Clause 2.9.

(b)

As far as practicable all field devices shall be supplied at voltages not exceeding ELV. Where voltage drop issues prevent the use of ELV field devices, the lowest practicable voltage shall be used and the circuit shall be protected by RCDs set to trip at 30 mA, and shall have an appropriate IP rating.

(c)

The risk management process shall consider the incorporation of vibration and temperature monitoring of each drive motor assembly, drive pulley and other major turning pulleys on the conveyor.

The risk management process should— (i)

address a means of isolation for individual conveyor drive or auxiliary motors; and

(ii)

consider the level of inter-tripping between multiple drive motors of the conveyor in the case that a fault occurs on any drive motor on that conveyor.

All discontinuous structures or frames of moveable conveyors shall be equipotentially bonded by fit-for-purpose flexible earth bonds to protect the electrical conductors and devices against lightning strikes and welding currents, and minimize indirect contact voltages.

NOTES: 1 It is assumed that moveable conveyors are such that induction hazards are minimized by either the length of the conveyor or separation from induction sources.

2 35 mm 2 flexible earth bonds are considered sufficient for this application.

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10.3 CABLES OF MOVEABLE CONVEYORS Where cables without semi-conductive sheaths, metallic screens or armouring are suspended from structures or frames of moveable conveyors, such structures and frames shall be considered as extraneous conductive parts and shall be included as part of the whole plant in the design of the protective measures against indirect contact (i.e. by ensuring that all metallic parts are linked together).

NOTE: It is assumed that moveable conveyors are such that induction hazards are minimized by either length of the conveyor or separation from induction sources.

10.4 BELT SPLICING EQUIPMENT Equipment used on site for the purposes of forming hot vulcanized spliced joints in conveyor belting shall, as a minimum, comply with the following: (a)

Splicing equipment shall comply with the requirements of Clauses 2.9, 2.10, 2.11 and 2.13.

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NOTE: Depending on the design of the splicing equipment, other parts of Section 2 may be applicable.

(b)

The splicing equipment shall have an earth leakage circuit-breaker having an earth leakage trip value not greater than 30 mA for protection of any hand-held electrical equipment used in conjunction with the splicing equipment.

(c)

The splicing control box shall contain circuitry that ensures the platens have an effective earth connection at all times (a form of pilot circuit will be regarded as complying with this requirement).

(d)

The resetting device for the short-circuit and earth leakage protection shall be capable of being locked to prevent unauthorized resetting.

(e)

The plug connecting the platen cable to the platen shall be secured with a retention device to ensure the plug cannot inadvertently come free from the platen.

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S E C T I O N 1 1 D E E P- WE L L T Y P E P U M P S S U R F A C E M I N I N G O P E R A T I O N S

A T

11.1 GENERAL This Section applies to deep-well pumps used in surface mining operations. It does not apply to pumps in operating underground mines.

Electrical supply to deep-well pumps operating in underground mines shall comply with the requirements of Appendix F. 11.2 RISERS AS PROTECTIVE CONDUCTORS Where a continuous metallic riser pipe is fitted between the motor and the well head, no protective conductor is required between the motor and the protective conductor connected directly to the fixed riser provided— (a)

the supply cable is terminated close to the well head;

(b)

the conductivity of the metallic riser (stand pipe) and the connections (couplings) is at least equal to the conductivity of the protective conductor which would otherwise be necessary; and

(c)

persons do not have access down the well.

11.3 CONTINUED OPERATION AFTER FIRST EARTH FAULT Accessed by Yancoal Australia Ltd on 17 Nov 2016 (Document currency not guaranteed when printed)

Operation may continue after the first earth fault only when— (a)

an impedance earthed IT system is used and all components are continuously rated for the level of earth fault and the resulting increased voltage that will occur on unfaulted phases;

(b)

the risk of tripping off the supply is greater than not tripping the supply; and

(c)

persons do not have access down the well.

Where operation may continue after the first earth fault, equipotential bonding shall be provided in accordance with Clause 11.4.

If a second earth fault is detected, the protective device shall automatically disconnect supply.

NOTE: Based on industry practice, a maximum of 10 A earth fault current limitation should be used.

11.4 EQUIPOTENTIAL BONDING An equipotential bonding conductor shall be installed between the main earth terminals of the supply and the well head(s), where the conductor shall be connected directly to the fixed riser. Where transformers are located at the well head, their enclosures shall be connected to this bonding conductor.

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The equipotential bonding conductor shall be so dimensioned that the voltage drop between any two points that may be contacted simultaneously will not exceed 50 V. That is— R≤

50 KI n

where R = resistance value between these two points, in Ohms In = rated current of the power fuses or, in the case of circuit-breakers, 0.2 times the releasing current for the instantaneous or short-time delay trip, in amperes K = a constant (a recommended value is 2.5) NOTE: The purpose of this requirement is to ensure that the voltage/time limits are not exceeded in respect of indirect contact between the various parts of the equipotential conductor.

11.5 EXEMPTION FROM INSULATION-MONITORING DEVICE For IT systems, an insulation-monitoring device (or earth fault detector) is not necessary to indicate the occurrence of the first earth fault provided the prospective touch voltage does not exceed 50 V and the conditions of Clause 11.2 are fulfilled.

11.6 DOUBLE LINE TO EARTH FAULTS

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For IT systems, a device, such as one which detects a change in neutral displacement on the occurrence of the first and second earth faults, may be used to disconnect the supply on the occurrence of the second earth fault.

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S E C T I O N 1 2 R E C L A I M A N D T R A N S F E R T U N N E L S F O R C O A L M I N E S 12.1 GENERAL Reclaim or transfer tunnels or parts of such tunnels for coal mines should be assessed in accordance with AS/NZS 3000 to determine if they contain hazardous areas (gas or dust or both). Because the characteristics of the coal being mined can change from time to time, the classification of these areas should be assessed for the full range of materials encountered during the life of the mine. Triggers for reassessment of these areas should be implemented, e.g. the detection of gas in underground workings.

NOTE: Particular care should be taken in cavities created for feeder systems and coal delivery chutes.

Where artificially driven ventilation is used, the classification in accordance with AS/NZS 60079.10.1 and AS/NZS 60079.10.2 shall take in consideration the failure of the ventilation system. When classified as a hazardous area, the electrical equipment shall be selected in accordance with AS/NZS 60079.14.

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NOTES: 1 Where electrical equipment selected in accordance with AS/NZS 60079.14 is required to have an EPL Ga, electrical equipment with an EPL Ma may be used.

2 Where electrical equipment selected in accordance with AS/NZS 60079.14 is required to have an EPL Gb, electrical equipment with an EPL Mb may be used.

3 Any automatic warning and tripping systems should be subjected to a functional safety analysis.

12.2 AUTOMATIC GAS MONITORING SYSTEM 12.2.1 Explosive atmospheres Where an explosive gas-monitoring system is provided, the following applies: (a)

The trip mechanism shall isolate the power supply to all non-explosion-protected equipment within the tunnel when the methane concentration exceeds 0.25%.

(b)

The trip mechanism shall isolate the power supply to equipment with an EPL of Mb or Gb when the methane concentration exceeds 1.25%.

NOTES: 1 The nominated concentrations of methane are levels that have traditionally been used in underground coal mines. These concentrations give a safety factor in excess of the typical safety factors specified in AS/NZS 60079.10.1.

2 Consideration should be given to leaving the ventilation fan running at the established trip points unless the concentration exceeds a point where the fan is at risk of being an ignition source.

3 A lockout mechanism should be fitted that will prevent the restoration of power until the trip mechanism is reset. Following an explosive gas trip it should not be possible to apply power to the equipment in the tunnel until the explosive gas concentration has fallen to safe levels.

4 There should be a visual indication of the gas level at all entry points and any control room.

5 Access to the reset mechanism should be restricted to authorized personnel.

6 The gas monitoring system should be maintained in accordance with AS 2290.3 or the principles of AS/NZS 60079.29.2.

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12.2.2 Irrespirable gasses Where a gas monitoring system is provided to detect irrespirable atmospheres, the following should apply: (a)

A warning should be given within a sufficient time to escape the irrespirable atmosphere. The time is dependent on the provision of any breathing aids provided to personnel and length and accessibility of the escape route.

(b)

The warning should be sufficient to prevent access into the tunnel.

(c)

There should be a visual indication of the oxygen level at each entry point.

12.2.3 Reclaim or transfer tunnel shutdown Consideration should be given to the shutdown of the conveyor when fire or flammable gases are detected. It may be necessary to run the conveyor clear of coal before bringing it to a stop.

12.2.4 Reclaim or transfer tunnel emergency lighting Reclaim or transfer tunnel emergency lighting should be designed and installed in accordance with AS 2293.1. The emergency lighting may need to be explosion-protected.

12.2.5 Stockpiles above reclaim or transfer tunnels Consideration should be given to interlocking stockpile feed conveyors such that discharge onto active work areas cannot occur.

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Indicators that show which reclaim tunnel feeders are operating should be visible from the active work areas.

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S E C T I O N 1 3 F I R E D E T E C T I O N A N D P R O T E C T I O N S Y S T E M S F O R E L E C T R I C A L A R E A S 13.1 GENERAL This Section sets out basic minimum requirements for protection of persons and plant from the hazards associated with fire, either originating from an electrical source or whose combustion could be supported by materials incorporated in the electrical installation, or where fire originating from another source could cause damage to the electrical installation.

The objective of this Section is to protect persons from the hazards of fire such as burns, noxious fumes or vapours, and insufficient oxygen for breathing.

Prevention of personal injury or loss of life by fire should be the first objective of fire protection. Where protection is required in this Section, it implies that the safety of persons may be otherwise jeopardized.

In many cases where property is jeopardized by fire, persons may also be jeopardized. In such cases, property protection is considered essential. In those cases where fire damage to property has no bearing on personal safety, protection of property is optional.

13.2 GENERAL PROTECTION REQUIREMENTS

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13.2.1 General Where a hazard resulting from fire has the potential to create personal danger, appropriate protection measures to mitigate risk, such as the installation of electrical and fire protection equipment, shall be taken.

NOTE: The reduction of property damage resulting from fire should also be taken into consideration when designing systems.

13.2.2 Analysis of need for protection A risk analysis of the equipment and installations shall be undertaken to determine the need for protection against fire and the means of providing such protection.

NOTE: For information on fire risk assessment, see ISO 16732-1.

The risk analysis should evaluate fire hazards with regard to the danger of the start and spread of fire, generation of smoke, gases or poisonous fumes, the possibility of flammable liquids being present, explosion and other occurrences endangering persons.

The analysis should establish the means to be used for detecting and giving an early warning of fire, normal and emergency means of escape, barriers or enclosures to prevent or contain the spread of fire, availability of firefighting personnel, and the type and quantity of fire extinguishment equipment.

A single extinguishment system may be used to protect against more than one hazard in a single area.

13.2.3 Means of protection 13.2.3.1 Protection by means of escape Means of escape is the route persons would follow to evacuate the workplace.

The means of escape shall be a well-defined, adequately marked and lighted passage, stairway or ramp.

NOTES: 1 A second or alternative means of escape may be necessary.

2 Emergency lighting (fixed or portable) may be required.

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13.2.3.2 Protection by portable means All electrical installations shall be equipped with portable fire extinguishing equipment suitable for the class of fire hazard likely at the installation. The equipment shall be available to all areas, easily visible, readily accessible, and so located that persons may have the option of either using this equipment or moving to a place of safety. Clear indication shall be provided on or adjacent to the unit of the method of operation and the class(es) of fire for which it is suitable.

NOTE: Portable units should be mounted to minimize damage and sealed to discourage misuse.

AS/NZS 1850 classifies portable fire extinguishers according to the general class(es) of fire for which they are suitable. AS 2444 sets out guidelines for the selection and location of portable fire extinguishers.

13.2.3.3 Protection by means of barriers and/or enclosures Barriers and/or enclosures constructed of materials having sufficient fire resistance to contain a fire or prevent fire penetration for an adequate period can be considered as a means of protection if they are installed so as to protect the workplace from exposure to fire and/or permit safe escape for personnel.

13.2.3.4 Protection by manually activated systems Where a fire hazard area is inaccessible thus preventing adequate protection by portable means, a manually operated fixed fire extinguishing system may be installed, provided persons are normally in attendance. The manual release device or devices shall be readily accessible in a fire situation and shall be capable of being initiated from a safe place.

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13.2.3.5 Protection by automatically activated systems Where a fire hazard area is inaccessible thus preventing adequate protection by portable means and persons are not normally in attendance, a fixed automatic fire extinguishing system may be installed. Automatically activated systems shall be capable of manual activation and the manual release device or devices shall be readily accessible in a fire situation and shall be capable of being initiated from a safe place.

13.2.3.6 Fixed detection, alarm and fire extinguishing systems and their equipment All fixed detection, alarm and fire extinguishing equipment and systems shall be selected and installed to suit the application, taking into account the class of fire(s) anticipated, operating conditions and area characteristics. The equipment and systems shall be installed by or under the general supervision of persons qualified for such installations.

NOTE: General supervision is where the supervisor does not have to be in attendance all the time but exercises control and direction that ensures the person can carry out the work required.

All detection and fire extinguishing equipment and systems shall be functionally tested after installation to ensure proper operation. Testing may not require discharge of the extinguishment medium.

NOTE: Attention is drawn to the following series: AS 1603, AS 1670, AS 7240 and AS 2118, which respectively deal with thermal detectors for fire alarm installations, automatic fire alarm installations, and automatic fire sprinkler systems.

13.2.3.7 Quantity and type of fire extinguishing medium available The quantity of fire extinguishing medium kept available at the particular area of fire hazard should be commensurate with the quantity of flammable material present, the nature of the extinguishment selected, the magnitude of the hazard to persons and the method of delivery of the medium.

Portable means of fire extinguishment are naturally limited in the quantity of medium contained. Where necessary, multiple units may be installed.

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Where gaseous fire systems are installed to accomplish total flooding of an enclosed volume, they shall meet the requirements of AS ISO 14520.1.

NOTE: Expert guidance should be sought to ensure the oxygen levels do not decrease below a safe level.

Fire extinguishing means applied to locations involving energized electrical equipment shall be safe in use. Unless appropriate precautions are taken to permit the use of conductive fire-extinguishing media, a non-conductive fire extinguishing medium shall be used.

Ambient temperatures shall be considered when selecting an appropriate fire extinguishing medium.

Fire blankets shall be supplied for smothering clothing fires in areas of high fire risk.

13.3 ADDITIONAL REQUIREMENTS AND RECOMMENDATIONS 13.3.1 Fire protection notices Notices indicating the location of fire-protection equipment shall be prominently displayed.

13.3.2 Protection of equipment or plant

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The following measures should be considered in order to minimize fire hazards for equipment or plant: (a)

Use of flame-retardant cables or, alternatively, coating of cables after installation with flame-retardant paint.

(b)

Installation of dry type power transformers.

(c)

Use of ‘less flammable oils’ in oil-filled transformers.

(d)

Wall panels, ceilings and false floors of control rooms and switch rooms constructed of non-combustible materials.

(e)

The use of cables that minimize dangerous by-products of combustion (e.g. low halogen cables).

13.3.3 De-energization of electrical equipment Provision shall be made for prompt de-energizing of electrical circuits and equipment involved in a fire.

Where automatic fire systems are installed, provision shall be made for the automatic removal of power to the area protected by the fire system.

13.3.4 Supplementary fire extinguishing equipment When the fixed fire extinguishing equipment is temporarily de-activated or otherwise rendered inoperative, alternative fire extinguishing equipment shall be made available. This may include portable equipment, gravity-feed water storage systems or self-contained fire water pumps.

Portable fire extinguishing equipment shall supplement fixed (manual or automatic) fire extinguishing equipment for early control of small fires.

13.3.5 Maintenance of fire protection systems Fire protection systems shall be maintained in accordance with AS 1851.

13.3.6 Ventilation systems and air conditioners Consideration shall be given to the need for shutting down, or redirecting ventilation systems in the event of a fire.

NOTE: Attention is drawn to AS/NZS 1668.1 and AS 2665, which respectively deal with fire precautions in buildings with air-handling systems and with smoke/heat venting systems.

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S T A T I C E L E C T R I C I T Y , S O U R C E S A N D I N D U C T I V E S O U R C E S

14.1 STATIC ELECTRICITY For the purpose of this Section, generation of static electricity is taken to mean the separation of electric charges into equal quantities of opposite polarity by disunion or relative movement between contacting surfaces of two substances having a different physical and/or chemical structure at the contacting surfaces. The substances may be both solids, both liquids, or one solid and one liquid. No static is generated by disunion or relative movement between gas and solids or gas and liquids, except where the gas contains entrained substances.

The requirements of AS/NZS 1020 shall apply.

14.2 ELECTROSTATIC PRECIPITATORS Where electrostatic precipitators and separators operating at high voltage are used, precautions, such as coded locks and interlocking, shall be taken to prevent access of personnel to high voltage areas having sufficient energy to create a hazard for personnel.

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14.3 RADIOACTIVE SOURCES The requirements of the ARPANSA Code of practice and safety guide for radiation protection and radioactive waste management in mining and mineral processing shall apply.

14.4 HAZARDS FROM INDUCTION Consideration shall be given to the possibility of hazards arising from induction from installations involving extremely high currents such as may exist with pot lines and arc furnaces. This applies particularly to the installation of cables in the vicinity of such equipment.

Consideration shall be given to the possibility of hazards arising from induction to installations of overland conveyors, pipelines, and other long metal structures which are located parallel to OHLs. When an OHL under construction, or de-energized for maintenance, is located close to another energized OHL, a potentially lethal voltage can be induced into the de-energized OHL by the electric field of the energized OHL and by the magnetic field arising from the OHL current. These voltages combined create a hazard that is dependent upon the length that the two OHLs run in parallel and inversely related to the distance between the two OHLs. In a similar manner, potentially lethal voltage can also be induced into overland conveyors, pipelines and other long metal structures by a nearby energized OHL.

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S E C T I O N 1 5 L A B E L S , S I G N A G E A N D I N F O R M A T I O N R E Q U I R E M E N T S A N D C O L O U R C O D I N G O F E N C L O S U R E S 15.1 GENERAL Single line distribution diagrams, maximum and minimum fault levels and protection settings for high voltage and low voltage distribution systems shall be provided and kept up to date. In all cases, the information shall be readily available to electrical personnel.

NOTE: A weatherproof enclosure located at the point of switching may be used to ensure single line diagrams are available to personnel.

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Labels and signs shall be provided to— (a)

comply with statutory regulations;

(b)

uniquely identify all electrical components, assemblies and associated equipment;

(c)

warn of the presence of electricity, including the voltage level;

(d)

provide advice of the action to be taken in the event of fire on the electrical equipment;

(e)

provide advice on the action to be taken in the event of electric shock or other electrical injuries;

(f)

identify the point or points of isolation necessary to make the electrical components and assemblies safe;

(g)

identify underground and hidden services;

(h)

appropriately and unambiguously indicate status and function of electrical components and assemblies;

(i)

clearly define closed electrical operating areas and access requirements for areas of either a permanent or temporary nature; and

(j)

clearly define arc flash energy levels and to advise that personnel protective equipment is required when performing any work in the proximity of switchgear.

15.2 SPECIFIC REQUIREMENTS Mine site standards shall be developed and documented for the mine site’s label and signage requirements. The standards shall cater for the following: (a)

Allocation of unique identifiers.

(b)

Consistent and appropriate presentation of information, by use of colours, symbols, format and size.

(c)

Materials of construction and installation.

Minimum requirements for labelling and signage of electrical equipment and assemblies shall be in accordance with AS 1318, AS 1319, AS 1755, AS 2293.1, AS/NZS 3000, AS 60204.1, AS 60204.11, AS 2067 and AS 2467, as applicable.

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Additional requirements for warning labels and signs shall be identified via a formal risk assessment. As a minimum the risk assessment shall take into consideration the following hazards: (i)

Risk of electric shock.

(ii)

Heat, fire and explosion.

(iii) Isolation. (iv)

Personnel movement and exposure to hazards.

(v)

Loss of safety and system integrity resulting from the removal of protective barriers, safety protective devices and electrical connections.

(vi)

Circuits requiring earthing.

(vii) Circuit earthing procedures.

15.3 ENCLOSURES CONDUCTORS

WITH

COVERS

GUARDING

ACCESS

TO

LIVE

To prevent inadvertent direct contact by persons, access covers of enclosures which provide access to live conductors above ELV, which either can be contacted by persons or are not protected by acceptable insulation material of thickness and grade appropriate to the voltage, shall be marked in accordance with Clause 15.2 and as follows: (a)

Reflective danger and warning labels shall be provided as required and determined by risk management.

(b)

Labels shall be permanently fixed in the appropriate location.

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Typical labels include the following: (i)

A warning label to be prominently displayed adjacent to each interlock switch with wording as follows: WARNING: SAFETY INTERLOCK—DO NOT OPERATE

(ii)

On any cover or door the removal or opening of which exposes live conductors: DANGER: XXXX VOLTS. (Highest voltage within the enclosure ) DANGER: ISOLATE ELSEWHERE BEFORE REMOVING COVER

(iii) In close proximity to the incoming supply and, where fitted, the through-bolted cable coupling adaptor or other connecting device: WARNING: THIS .................. IS NOT CONTROLLED BY THIS SWITCH

(iv)

In proximity to all high voltage cable coupling adaptors: WARNING: PRIMARY SIDE CABLE ADAPTORS ARE NOT ISOLATED BY OPENING THIS PRIMARY SIDE CIRCUIT DISCONNECTOR

(v)

In proximity to any off-load tap changing device: DANGER: OFF-LOAD TAP CHANGER—DO NOT ALTER SETTING WHEN ENERGIZED

15.4 VOLTAGE IDENTIFICATION OF ELECTRICAL ENCLOSURES Where multiple voltages exist within the one operating area, a site-consistent means of clear identification of the various voltage levels shall be provided.

NOTES: 1 One method that may be used is colour coded enclosures.

2 Preferred colours for electrical equipment are orange (X15) for low voltage switchboards up to 690 V; harbour blue (B24) for 1 kV; and signal red (R13) for high voltage. These colours are defined in AS 2700.

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O P E R A T I O N A L

R E Q U I R E M E N T S

16.1 GENERAL This Section specifies the normal operating procedures that shall be developed and implemented to ensure the safety of personnel. These procedures may be varied in certain circumstances where a planned operation is performed under controlled conditions.

NOTE: Attention is drawn to the fact that the requirements of regulatory authorities may differ from the requirements specified in this Standard.

A site-specific risk assessment shall be undertaken to identify risks presented by the electrical distribution system and assess the suitability of the risk controls in place.

16.2 RESTRICTIONS ON ACCESS BY PERSONNEL 16.2.1 Identification of closed electrical operating areas Closed electrical operating areas shall be identified prominently with signs.

16.2.2 Access to closed electrical operating areas The mine site shall have a procedure in place to restrict access to closed electrical operating areas to authorized persons and persons under the direct supervision of authorized persons.

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A risk assessment shall be undertaken and the identified risk controls implemented for each type of operation and routine work that takes place within a closed electrical operating area.

NOTES: 1 Consideration should be given to the types of equipment and tools used within the closed electrical operating area and their potential for direct contact with energized equipment.

2 Special consideration should be given to concurrent work activities, e.g. the entry of a cleaner to an area in which switching may take place.

16.3 OPERATIONS INVOLVING PERSONNEL WORKING IN THE VICINITY OF EXPOSED LIVE PARTS 16.3.1 Low voltage Work (including testing) on low voltage systems shall comply with AS/NZS 4836.

16.3.2 High voltage Work on assets owned by the network service provider shall be carried out in accordance with the procedures of the network service provider.

Work on mine-owned assets shall only take place with the assets de-energized. For high voltage installations, in addition to isolation of the circuit and checking that it has been de-energized (often referred to as ‘checking for dead’), all active conductors shall be earthed. A skilled person shall ensure that the isolation and application of the earths have been satisfactorily completed, and shall give authorization before the commencement of any work. For testing purposes, the earths may be temporarily removed provided appropriate measures are adopted to ensure the safety of personnel.

A skilled person shall ensure that all persons who are to work on the parts are fully conversant with the isolated area and the work to be carried out. The skilled person shall be aware of the possibility of dangerous voltages being induced from adjacent energized conductors and, where necessary, shall ensure that appropriate precautions are taken.

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Where there are adjacent exposed live parts that cannot be safely isolated from the work area by the use of protective barriers, the exposed live parts shall be isolated and, where applicable, short-circuited and earthed, and shall be clearly identified and precautions taken to avoid contact with the exposed live parts.

A ‘high voltage access permit procedure’ shall be established to safeguard work on or in close proximity to exposed high voltage conductors. Electrical workers shall be instructed in this procedure. Work in close proximity to high voltage equipment shall not be permitted unless authorized by a ‘high voltage access permit’. A ‘ground excavation permit procedure’ shall be established to safeguard persons required to excavate ground in the vicinity of cables buried in the ground. Workers shall be instructed in this procedure.

Excavation work in the vicinity of buried cables shall not commence unless authorized by a ‘ground excavation permit’.

16.3.3 Use of stop controls Stop controls shall not be used for the purpose of isolation or immobilization to allow work to be carried out on parts which would otherwise be electrically energized or capable of moving.

16.3.4 Use of interlocking Control circuit interlocking shall not be relied upon as a means of isolation to gain access to enclosures supplied with greater than extra-low voltage.

The interlocking of restrained plugs and receptacles shall not be relied upon as a means of isolation.

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16.4 USE OF RADIO REMOTE CONTROL EQUIPMENT Spectrum management for radio-controlled equipment shall be taken into consideration.

NOTE: For remote control systems for mining equipment, see AS/NZS 4240 (series).

16.5 OVERHEAD LINES Work near overhead lines shall comply with AS/NZS 7000.

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SECTI ON 17 A L T E R A T I O N S T O

MANAGE MENT OF T H E M I N I N G O P E R A T I O N

17.1 GENERAL Care shall be taken to ensure that compliance with this Standard is maintained when the electrical system and/or mining operation is altered. Review of any proposed change shall take into consideration the impacts on operational and maintenance activities of the immediate plant affected by the change and of surrounding mining operations and plant.

Such alterations may include— (a)

extending the area of mining operation (requiring longer OHLs or cables);

(b)

construction of roads;

(c)

addition, or substitution, of equipment;

(d)

change to operating procedures;

(e)

change to equipment ratings; or

(f)

change to power supply arrangement.

Matters that should be considered include— (i)

clearances;

(ii)

guarding of electrical installations;

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(iii) protective conductor size; (iv)

overload and short-circuit protection;

(v)

under-voltage;

(vi)

exposure to lightning;

(vii) prospective touch voltages; (viii) fault level and equipment fault rating; and (ix)

integrity of safety systems.

Before changes are made to distribution networks, a check shall be conducted to ensure that the changes will not adversely affect the supply to safety critical infrastructure.

17.2 MANAGEMENT OF CHANGE Any intended alteration to the ‘as built’ documented operation or electrical installation shall be implemented under a ‘modification control’ system.

The ‘modification control’ system should include the following measures: (a)

Preparation: (i)

Scope defined and design prepared.

(ii)

Appropriate level of risk assessment is conducted on the proposed design.

(iii) Opportunity for other stakeholders and non-electrical disciplines to have input. (iv)

Concept review and approval process prior to final design and implementation.

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Implementation: (i)

Detailed design.

(ii)

Review, validation and approval of final design prior to implementation and commissioning.

(iii) All work is implemented and commissioned under a site work order system. (c)

Close out: (i)

The plant technical record of drawings and procedures are ‘as built’ to reflect the implemented changes.

(ii)

The mine plan and other relevant documents are updated to accurately show the changes.

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(iii) Stakeholders and the initiator of the change sign off on satisfactory implementation.

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APPENDIX A

TN, TT AND IT SYSTEMS DESCRIPTION (Informative) A1 GENERAL The codes used in the description of the systems have the following meaning: (a)

First letter The relationship of the earthable point of the power system to earth, as follows: T = direct electrical connection (minimum practical impedance) to earth.

I

= no connection (all live parts isolated from earth) or connected to earth through an impedance (resistor or reactor) or equivalent circuit.

NOTE: In three-phase systems, the earthable point is commonly the neutral point of the generator or transformer.

(b)

Second letter The relationship of the exposed conductive parts of the electrical installation to earth, as follows: T = direct electrical connection (minimum practical impedance) to earth, independently of any connection to the earthable point of the power system.

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N = direct electrical connection (minimum practical impedance) to the earthable point of the power system.

Where the characteristics of the system of earthing of the supply to the electrical installation are not known, they should be ascertained from the power supplier.

A2 DESCRIPTION OF THE SYSTEMS The following distinction is made with regard to the system of earthing: (a)

TN system (Figures A1, A2, and A3) Power systems having the earthable point directly connected to earth, the exposed conductive parts of the installation being connected by protective conductors to the earthable point of the power system.

(b)

TT system (Figure A4) Power systems having the earthable point directly connected to earth, the exposed conductive parts of the installation being connected to earth electrodes which are electrically independent of the earth electrodes of the power system.

(c)

IT system (Figures A5, A6, A7) Power systems having the earthable point not connected to earth, or connected to earth through deliberately inserted impedance (resistor or reactor), the exposed conductive parts of the installation being connected to earth electrodes which may be the same as those used for the earthing resistor or reactor.

(d)

Zero sequence reactor system Power systems deriving supply from other systems (TT or TN) through a three-phase reactor (zero sequence reactor) offering a high impedance to earth fault (zero sequence) currents with neutral displacement. An earth fault current-limiting neutral displacement reactor is intended for use in series with a three-phase system. The earthable point (the neutral point in this case) is earthed, providing low impedance to load current but high impedance to zero sequence currents in order to limit to a specified value the current which would occur under a single phase-to-earth fault. Normally reactors of this type are used only on systems above 1000 V. Such a reactor may be used in lieu of an isolating transformer for the purpose of restricting earth fault currents.

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A3 PROTECTIVE MEASURES FOR TN SYSTEMS A3.1 General

L1 Powe r sys te m e a r th a b l e p o i n t

L2 L3 N PE

E a r th E x p o s e d c o n d u c tive p a r t s

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FIGURE A1 POWER SYSTEM TN WITH SEPARATE NEUTRAL AND PROTECTIVE CONDUCTORS THROUGHOUT THE SYSTEM

L1 Powe r sys te m e a r th a b l e p o i n t

L2 L3 PE PEN N

E a r th E x p o s e d c o n d u c tive p a r t s

E x p o s e d c o n d u c tive p a r t s

FIGURE A2 POWER SYSTEM TN WITH NEUTRAL AND PROTECTIVE FUNCTIONS COMBINED IN A SINGLE CONDUCTOR IN A PART OF THE SYSTEM

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Powe r sys te m e a r th a b l e p o i n t

L2 L3 PEN

E a r th E x p o s e d c o n d u c tive p a r t s

FIGURE A3 POWER SYSTEM TN WITH NEUTRAL AND PROTECTIVE FUNCTIONS COMBINED IN A SINGLE CONDUCTOR THROUGHOUT THE SYSTEM

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In TN systems, the earthable point (in three-phase systems commonly the neutral point of the power system) and exposed conductive parts are interconnected by a protective conductor. In the case of a short-circuit from a phase conductor to the protective conductor or exposed conductive parts, the resultant fault current initiates, through a protective device, disconnection of the supply to the defective equipment.

To ensure that, in case of a fault (to exposed conductive parts or to earth), the potential of the protective conductor and of the exposed conductive parts connected to it differs as little as possible from the earth potential, the protective conductor should be connected to a number of earthing points distributed so as to obtain the lowest practical earthing impedance.

A3.2 Bonding of exposed conductive parts A3.2.1 General All exposed conductive parts of the electrical installation should be connected to the earthable point of the power system by protective conductors.

A3.2.2 Single conductor as combined protective and neutral conductor A single conductor may combine the functions of a protective and neutral conductor, provided— (a)

the conductor is non-flexible and in a fixed electrical installation;

(b)

the cross-sectional area of the conductor is not less than 10 mm 2; and

(c)

the conductor is not supplied through a residual-current-operated protective device.

In those instances where the conductor may be bare (i.e. without insulation), it may be necessary to insulate the conductor for reasons other than protection against indirect contact (e.g. fire risk).

A3.2.3 Interruption of combined protective and neutral conductor The protective conductor should not be interrupted in service. Overcurrent-operated protective devices are admissible in a combined protective and neutral conductor only where they also interrupt the phase conductors.

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A3.2.4 Separation of protective conductor from a combined protective and neutral conductor If from any point of the electrical installation, the neutral and protective conductors are separated, it is inadmissible to connect these two conductors to each other from that point on toward the load.

The neutral conductor should be insulated and installed in the same manner as a phase conductor.

A4 PROTECTIVE MEASURES FOR TT SYSTEMS A4.1 General

L1 Powe r sys te m e a r th a b l e p o i n t

L2 L3

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N

E a r th E x p o s e d c o n d u c tive p a r t s

PE

E a r th

FIGURE A4 POWER SYSTEM TT

In TT systems, the earthable point (neutral point) is directly connected to an earth electrode with no impedance (other than the impedance of the protective conductor) being inserted between the earthable point and the earth electrode.

The exposed conductive parts are connected, either individually, in groups, or as a whole, to one or several earth electrodes independent of the earth electrode of the earthable point.

For systems wholly contained within moveable or mobile machinery, the metallic structure should form the earth electrode and the earthable point should be connected to the metallic structure.

In the event of a fault between a phase conductor and an exposed conductive part, the touch voltage should be limited to safe levels.

A4.2 Neutral conductor insulation and installation The neutral conductor, if any, should be insulated and installed in the same manner as a phase conductor.

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A4.3 Bonding of exposed conductive parts All exposed conductive parts of electrical equipment protected by a common protective device should be interconnected and connected by a protective conductor to a common earth electrode. If several protective devices are used in series, this requirement applies to each group of exposed conductive parts protected by the same device.

Exposed conductive parts which are simultaneously accessible should be connected to a common earth electrode.

A4.4 Protective devices The use of the following protective devices is recommended: (a)

Residual-current-operated protective devices.

(b)

Overcurrent-operated protective devices.

The use of fault-voltage-operated protective devices is not excluded for systems up to and including 1000 V. A5 PROTECTIVE MEASURES FOR IT SYSTEMS A5.1 General

L1 Powe r sys te m e a r th a b l e p o i n t

L2

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L3 E a r th i n g impedance (r e s i s to r o r r e a c to r) where installed

PE E a r th

E x p o s e d c o n d u c tive p a r t s

E a r th

FIGURE A5 POWER SYSTEM IT WITH INDEPENDENT EARTH ELECTRODES

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Powe r sys te m e a r th a b l e p o i n t

L2 L3

E a r th i n g impedance (r e s i s to r o r r e a c to r) where installed PE

E a r th

E x p o s e d c o n d u c tive p a r t s

FIGURE A6 POWER SYSTEM IT WITH COMMON EARTH ELECTRODE

L1 E x te r n a l sys te m TN or T T

L2

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L3

E x te r n a l p owe r sys te m e a r th a b l e point

E a r th c u r r e nt li m i ti n g n e u tr a l d i s p l a c e m e n t r e a c to r (ze r o s e q u e n c e r e a c to r)

PE E x p o s e d c o n d u c tive p a r t s

E a r th

E a r th

FIGURE A7 POWER SYSTEM IT USING EXTERNAL TT OR TN SYSTEM AS A SOURCE

In IT systems, the earthable point of the power system is either isolated from earth or earthed through an impedance, and the exposed conductive parts are connected to one or several earth electrodes either individually, in groups or as a whole.

A system in which supply is taken from a TN or TT power system through an earth fault current-limiting neutral displacement reactor (zero sequence reactor) restricting the earth fault current to a low value complies with the definition of an IT system.

AS/NZS 3000, AS 60204.1 and AS 60204.11 generally focus on TN systems; however, impedance earthed IT systems utilizing resistance grounding have been successfully used to manage the risks from indirect contact at many mining operations.

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Impedance earthed IT systems may— (a)

significantly reduce the earth potential rise with a consequent reduction in touch and step voltages and transfer potentials;

(b)

in conjunction with sensitive earth leakage protection, significantly reduce the damage sustained by electrical equipment under earth fault conditions;

(c)

reduce the likelihood of an earth fault propagating into a multi-phase arc flash/blast event. This reduction is because the destruction and melting of copper is generally insignificant with the low earth fault current and therefore propagation into a multiphase fault is highly unlikely; and

(d)

significantly reduce the arc flash and incident energy under earth fault conditions (by a number of orders of magnitude) compared to solidly earthed systems.

Further information on the principles of earth fault limited systems is given in AS/NZS 2081.

Further information on the installation and use of earth fault current limitation devices is given in AS/NZS 2081.

A5.2 Artificial earthable point The use of artificial earthable points is recognized.

NOTE: Such earths may be necessary in order to reduce over-voltage or oscillations.

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A5.3 Star point conductor in IT systems With an IT connected system, the star point, or centre tap of the transformer connection, to the earth fault limiting device, and the earth fault limiting device to earth, should be sized and installed to ensure a high integrity.

Precautions should be taken to ensure the cable, earth fault-limiting device and connections are not subjected to physical damage/stress from impacts or vibration.

A5.4 Bonding of exposed conductive parts All exposed conductive parts should be earthed individually, in groups or as a whole and may be connected directly to the earth (see Figures A5 and A6).

The total earthing resistance (R A) of all exposed conductive parts connected by the protective conductor to an earth electrode should satisfy the following:

I d × RA ≤ U L where Id = fault current in the case of the first dead fault between a phase conductor and an exposed conductive part The value of Id takes into account the leakage currents and the total earthing impedance of the electrical installation.

UL = prospective touch voltage A5.5 Protective devices The use of the following protective devices is recommended: (a)

Insulation-monitoring devices.

(b)

Overcurrent-operated protective devices.

(c)

Residual-current-operated protective devices.

(d)

Residual-voltage-operated protective devices (only for special applications).

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A5.6 Neutral conductor in IT systems Loads should not be supplied from the neutral of an IT system. If a single-phase load has to be connected to these systems then it has to be done via an isolation transformer. This ensures that an earth fault on the neutral will not bypass the earth fault current limitation device.

The issue is that the touch potential of the neutral is no longer the same as the earth system.

Under certain fault conditions the following issues arise: The prospective touch voltage may increase.

(b)

An earth fault on the neutral will bypass the NER, resulting in an unrestricted earth fault.

(c)

The backup earth fault protection may not see the fault as it is bypassed.

(d)

The earth fault detection relay may not be suitable for use in a system with an unlimited earth fault and therefore may not register the earth fault, even if not bypassed.

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(a)

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APPENDIX B

PROTECTIVE DEVICES AND THEIR USES (Informative) B1 SELECTION OF PROTECTIVE DEVICES AND PROTECTION SYSTEMS B1.1 Introduction This Appendix sets out factors which should be taken into account in the selection of protective devices and protection systems.

It refers to the criteria which needs to be satisfied for protection against the effects of— (a)

short-circuit, on conductors and equipment;

(b)

overload, on conductors and equipment;

(c)

indirect contact; and

(d)

gives examples of the devices and/or measures which may be used to provide this protection.

Also given are characteristics of certain protective devices.

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The selection of protective devices should be based on sound electrical protection principles and provided for the safe operation of the electrical equipment and outgoing circuits, including the protection of persons and the operating environment.

Protection settings should be in accordance with the mine’s electrical protection scheme.

Protection devices should comply with the relevant standard (IEC 60255 series, AS/NZS 2081).

The ANSI reference codes used within this Section are as per ANSI/IEEE C37.2.

A single device may be used to protect more than one circuit if it satisfies the requirements for each of the circuits involved.

NOTE: This may compromise efficient diagnosis of faults and restoration of power to unfaulted parts of the system. It is recommended that each individual load have its own protective devices.

B1.2 Operating characteristics Where separate sensing, auxiliary and interrupting devices are used, the combined characteristics of all auxiliary devices should be taken into consideration (e.g. the total operating time of all devices).

B1.3 Discrimination between protective devices Where discrimination is required for reasons of safety, the characteristics of the protective devices should be such that only the protective device selected for the particular circuit abnormality is caused to operate, and disconnection involves the minimum number of elements of the power system necessary for safely clearing the circuit abnormality.

B2 PROTECTIVE DEVICES B2.1 General Modern protection relays can have multiple protection functions. Some of these are described in Paragraphs B2.2 to B2.35.

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B2.2 Measuring transformers Current and/or potential transformers may be necessary to reduce the magnitude of currents and/or voltages supplied to protective devices, or to provide isolation. The transformers should be selected so that their characteristics are adapted to and coordinated with the characteristics of the protective device. Requirements for current transformers and voltage transformers are specified in AS 60044 (series).

B2.3 Residual-current-operated protective devices Residual-current-operated protective devices detect a condition of insulation failure of the circuit being protected by measuring the leakage current, residual current or zero phase sequence current.

Residual-current-operated protective devices may be employed in all power systems but are not recommended for those forms of TN system where the neutral and the protective conductors are combined.

B2.4 Residual-voltage-operated protective devices Residual-voltage-operated protective devices detect a condition of insulation failure of the circuit being protected by measuring the displacement of system voltage vectors from the normal state, or the residual voltage. Loss of one phase in a multi-phase system may also result in the operation of this form of device.

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Residual-voltage-operated protective devices are most commonly employed in IT power systems. A single device is sufficient to detect an earth fault on any part of an IT system in which all elements are directly connected, i.e. not coupled through a transformer, capacitor or resistor.

B2.5 Fault-voltage-operated protective devices Fault-voltage-operated protective devices (also known as voltage-operated earth leakage circuit-breakers) detect the voltage between exposed conductive parts and an independent earth electrode adequately separated from the main earth electrode. Correct operation depends on the integrity of the independent earth electrode system.

The use of fault-voltage-operated protective devices is restricted to small, low-capacity branches of a TT system with voltages below 1000 V where satisfactory earthing conditions cannot be achieved.

B2.6 Combined residual-current/voltage-operated protective devices Protective devices employing a combination of residual voltage and residual current detection may be employed on all power systems to indicate the direction of the earth fault current from the point of measurement. Such devices may detect and locate sustained faults, detect and locate transient faults and, if necessary, differentiate between earth faults and transient line conditions.

B2.7 Insulation-monitoring devices Insulation-monitoring devices continuously measure and monitor the insulation resistance in unearthed systems.

In selecting the most suitable device for a particular application, it should be noted that certain protective devices will indicate faults in loads connected through rectifiers or thyristors, whilst others will not.

NOTE: Measuring circuits of several insulation monitors should not be connected in parallel, which might occur, for example, when supply systems are coupled.

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B2.8 Distance relays Distance relays may be used in certain cases to protect high voltage power transmission systems against faults involving only phase conductors, or involving phase conductor(s) and earth.

By comparing fault current and voltage at the point of installation of the relay, distance to the fault is measured.

Appropriate selection of settings and corresponding relay operating times enable a distance relay to provide high speed clearing of faults in a particular section of the power system, as well as providing backup protection.

B2.9 Differential protection Differential protection detects the occurrence of a fault by comparing signals delivered by current transformers which are located at each end of the zone to be protected.

The systems have the advantage of providing— (a)

high sensitivity;

(b)

instantaneous detection; and

(c)

discrimination between the protected zone and other parts of the system.

The system is insensitive to faults occurring outside the protected zone.

B2.10 Overcurrent-operated protective devices

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B2.10.1 General Overcurrent-operated protective devices are used to measure and protect circuits and equipment against the effects of both short and long term overcurrents. They may be either directional or bi-directional and either direct or indirect acting devices.

Overcurrent-operated protective devices in common use include the following: (a)

Fuses.

(b)

Magnetically operated circuit-breakers or switches.

(c)

Thermally operated circuit-breakers or switches.

(d)

Current-transformer-operated magnetic and/or thermal relays.

(e)

Current-transformer-operated solid state relays.

Fuses and circuit-breakers with their associated sensing and auxiliary devices should be selected so that— (i)

they can withstand the maximum prospective short-circuit current; and

(ii)

they will disconnect the protected circuit in an appropriate time when the minimum prospective short-circuit current occurs. The minimum prospective short-circuit current is taken as that corresponding to a short-circuit of negligible impedance at the most distant point of the protected circuit.

NOTE: Whilst it is accepted practice to set short-circuit tripping levels at a maximum of 50% of the minimum prospective three-phase bolted fault level, consideration should be given to lower settings to control the arc flash energy levels.

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B2.10.2 Thermal overload ANSI code 49 RMS This protection is used to protect equipment (motors, transformers, generators, lines, capacitors) against overloads, based on measurement of the current consumed. The protection gives a trip order when the heat rise, calculated according to the measurement of an equivalent current Ieq, is greater than the set point.

The protection tripping time is set by the time constant as follows: (a)

The calculated heat rise depends on the current consumed and the previous heat rise state.

(b)

The cold curve defines the protection tripping time, based on zero heat rise.

(c)

The hot curve defines the protection tripping time, based on 100% nominal heat rise.

B2.10.3 Phase overcurrent ANSI code 50/51 Phase overcurrent protection is three-phase, and picks up if one, two or three of the phase currents reach the operation set point. There may be an alarm set point connected to the operation of the protection function indicating the faulty phase or phases. It includes a time delay, which is either definite time (DT), (constant, DT) or inverse definite minimum time (IDMT) depending on the curves selected.

B2.11 Loss of vacuum/frozen contact protection devices

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Loss of vacuum/frozen contact protection devices operate to detect— (a)

the switching device failing to open when required (e.g. welded contacts); and

(b)

the loss of the insulating medium of the switching device.

The protection should prevent re-closure of the circuit under the above conditions. Facilities should be provided to prevent resetting by unauthorized persons.

Loss of vacuum/frozen contact protection devices should comply with the requirements of AS/NZS 2081.

Further information on the installation and use of frozen contact protection devices is given in AS/NZS 2081.

B2.12 Under/overpressure protection devices Equipment that is dependent upon the maintenance of a relatively constant pressure within its enclosure should be fitted with a pressure-sensing device to automatically cut off the power supply to the incoming switching device when the pressure reaches a predetermined value.

B2.13 Earth-continuity protection devices Earth-continuity protection devices complying with the performance and construction requirements of AS/NZS 2081 should be used to protect any circuit employing restrained receptacles or supplying mobile or portable equipment through trailing or reeling cables.

In the event that the earth impedance exceeds the value as nominated in the mining operations earth protection scheme, the device should cause a switching device controlling the power to the supply cable to— (a)

open, if it is in the closed position; and

(b)

not to close if it is in the open position.

Each earth-continuity monitoring circuit should have a test facility to verify the operation of the protection system.

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B2.14 Earth leakage protection On external circuits where the supply is above ELV, earth-leakage protection devices should be used to detect earth-leakage currents and should comply with the design and construction requirements of AS/NZS 2081.

Facilities to prevent resetting by unauthorized persons should be provided.

Each earth leakage protection circuit should have a test facility to verify the operation of the protection system. The test leakage current should not exceed 1.2 times the earthprotection trip setting.

B2.15 Earth fault lockout protection Where power is supplied to a mobile or portable machine by a trailing or reeling cable, protection should be provided to prevent the introduction of electrical power if an earth fault is detected on the circuit to be energized.

Lockout earth fault protection devices should comply with the requirements of AS/NZS 2081.

Further information on the installation and use of earth fault lockout protection devices is given in AS/NZS 2081.

B2.16 Neutral-connected current limitation system integrity protection

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For low voltage systems, where an earth fault current limitation device is used, a facility should be provided to test the state of the earth fault current limitation circuit. This may be a current-limited phase-to-ground test for testing of earth leakage or a neutral monitoring device.

Where a neutral monitoring device is used, it should comply with the performance and construction requirements of AS/NZS 2081.

For high voltage systems, consideration should be given to the use of a neutral monitoring device.

NOTE: The purpose is to ensure the earth fault current limitation circuit remains effective. An open circuit failure would allow a single earth fault to go undetected, and a second earth fault may then create unsafe touch voltages.

B2.17 Undervoltage ANSI code 27/27S The protection function is three-phase and operates according to parameter setting with phase-to-neutral or phase-to-phase voltage. It picks up if one of the three phase-to-neutral or phase-to-phase voltages drops below the Us (or Vs) set point.

The function can include a definite time delay, to allow for voltage drops due to large drives starting, etc.

B2.18 Positive sequence undervoltage ANSI code 27D The protection picks up when the positive sequence component Vd of a three-phase voltage system drops below the Vsd set point. The function may include a definite time delay, to allow for voltage drops due to large drives starting, etc. It allows drops in motor electrical torque to be detected.

B2.19 Phase rotation direction check ANSI code 27D/47 This protection allows the phase rotation direction to be detected. The protection considers that the phase rotation direction is inverse when the positive sequence voltage is less than 10% of Unp and when the phase-to-phase voltage is greater than 80% of Unp. B2.20 Remanent undervoltage ANSI code 27R This protection is single-phase, and it picks up when the phase-to-phase voltage is less than the set point. The protection includes a definite time delay.

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B2.21 Directional active overpower ANSI code 32P This function may be used as ‘active overpower’ protection for energy management (load shedding) or ‘reverse active power’ protection against motors running like generators and generators running like motors. It picks up if the active power flowing in one direction or the other (supplied or absorbed) is greater than the set point. It includes a definite time delay.

B2.22 Directional reactive overpower ANSI code 32Q/40 This protection function is used to detect field loss on synchronous machines (generators or motors) connected to the network. In both cases, the machine undergoes additional temperature build-up, which may damage it. It picks up if the reactive power flowing in one direction or the other (supplied or absorbed) is greater than the set point. It includes a definite time delay.

B2.23 Phase undercurrent ANSI code 37 This protection is single-phase and it picks up when phase 1 current drops below the set point. It includes a definite time delay T. B2.24 Temperature monitoring ANSI code 38/49T This protection is associated with an RTD of the Pt100 platinum (100 Ω at 0°C or 2°F) or Ni 100 or Ni 120 nickel type in accordance with IEC 60751.

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It picks up when the monitored temperature is greater than either— (a)

the alarm set point; or

(b)

the tripping set point.

When the protection is activated, it detects whether the RTD is shorted or disconnected.

B2.25 Negative sequence/unbalance ANSI code 46 This protection function is determined according to the three-phase currents, and picks up if the negative sequence component of phase currents is greater than the operation set point. It is time delayed. The time delay may be definite time or IDMT according to a standardized curve.

B2.26 Broken conductor ANSI code 46BC The purpose of broken conductor detection protection is to indicate, on a radial high voltage network, the opening of a phase at a point on the circuit.

This may have several origins, including— (a)

broken conductor on the ground at the source end;

(b)

broken conductor on the ground at the load end; or

(c)

open wire without conductor on the ground due to— (i)

a broken conductor;

(ii)

a blown fuse; or

(iii) a problem with a circuit-breaker phase.

Broken conductor detection protection is based on the negative sequence and positive sequence current ratio, which makes it independent of the load fluctuations on the network.

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These performances depend on the following: (A)

(B)

The installation: (1)

The transformer neutral earthing system.

(2)

Capacitive current.

(3)

Presence of a permanent negative sequence.

The nature of the fault and subsequent considerations such as— (1)

broken conductor with either one end on the ground at the source end, or one end on the ground at the load end, or no end touching the ground;

(2)

distance between the protection relay and the location of the break; and

(3)

fault impedance.

The impedance depends mainly on the nature of the ground where the fault occurred.

B2.27 Negative sequence overvoltage ANSI code 47 The protection function picks up if the negative sequence component of the voltages is above the set point. It includes a definite time delay.

B2.28 Excessive starting time locked rotor ANSI code 48/51LR/14

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This function is three-phase, and comprises two parts: (a)

Excessive starting time During starting, the protection picks up when one of the three-phase currents is greater than the set point for a longer period of time than the ST time delay (normal starting time).

(b)

Locked rotor The normal operating rate (after starting), the protection picks up when one of the three-phase currents is greater than the current set point for a longer period of time than the locked rotor time delay of the definite time type.

B2.29 Breaker failure ANSI code 50BF This protection is designed to detect the failure of breakers that do not open when a tripping order is sent. The ‘breaker failure’ protection function is activated by a tripping order received from the overcurrent protection functions (50/51, 50 N/51 N, 46, 67 N, 67). It checks for the disappearance of current during the time interval specified by the time delay.

It may also take into account the position of the circuit-breaker read from logic inputs to determine the actual opening of the breaker. Wiring a volt-free closed circuit-breaker position contact on the ‘breaker closed’ equation editor input ensures that the protection is effective in the following situations: (a)

When 50 BF is activated by protection function 50 N/51 N (set point Is0 < 0.2 In), detection of the 50 BF current set point can possibly be not operational.

(b)

When trip circuit supervision (TCS) is used, the closed circuit-breaker contact is short-circuited.

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B2.30 Earth fault ANSI code 50N/51N or 50G/51G Earth fault protection is based on measured or calculated residual current values.

Earth fault protection picks up if the earth fault current reaches the operation set point of the residual earth fault current summated in the relay from all measured phases.

Ground fault protection picks up if the ground fault current reaches the operation set point of the measured ground fault current, typically via dedicated toroid summated current transformers.

Both earth and ground fault protection includes a time delay, which is either definite (constant, DT) or IDMT, depending on the curves selected.

B2.31 Starts per hour ANSI code 66 This protection picks up when the number of starts reaches the following limits: (a)

Maximum number of starts (Nt) allowed per period of time (P).

(b)

Maximum allowed number of consecutive hot starts (Nh).

(c)

Maximum allowed number of consecutive cold starts (Nc).

B2.32 Directional overcurrent (67) and directional earth fault (67N) These protection schemes combine conventional overcurrent and earth fault schemes with a voltage reference to determine direction of the fault. In distribution or transmission networks with parallel feeders or closed rings, directional schemes will enable separate tripping responses to faults in the forward and reverse directions.

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B2.33 Neutral voltage displacement (59N) This protection scheme is used to detect phase-earth faults in IT systems whereby either high impedance neutral earthing is employed or the system has no reference to earth. These schemes are non-directional and measure the displacement of the system neutral during earth faults.

B2.34 Volt/Hertz (24) Otherwise known as over-fluxing protection, these Volt/Hertz schemes protect rotating machines and transformers from system conditions of over-voltage or under-frequency, which may result in damage from excessive magnetic flux density. The problem with overfluxing is that when the magnetic circuit exceeds the design flux density, the laminated core cannot contain the flux and it will extend to other parts causing eddy currents and overheating in a very short time. In the case of synchronous machines, problems with automatic voltage regulator control are also intercepted by over-fluxing schemes.

B2.35 Bus overcurrent blocking schemes Compared to public electrical distribution infrastructure, mines and associated processing plant are often topographically compact installations with multiple protection devices along feeders. This often leads to difficulties in achieving inverse time grading, which can be overcome with blocking schemes in place between switchboard feeders and incomers. The principle of a blocking scheme relies on the feature of multiple setting groups in a relay whereby an incomer and feeder are both set to trip at the same characteristic. For downstream faults, the feeder relay provides a blocking signal on fault pickup to the incomer relay and inhibits timing while the feeder clears. In some cases, blocking scheme logic enables alternative and slower settings in the incomer. In the case whereby the fault is within the switchboard, the incomer does not receive the blocking signal from the feeder and trips against the original characteristic.

B3 PROTECTION ARRANGEMENTS FOR TRANSPORTABLE SUBSTATIONS Figure B1 depicts examples of protection arrangements for transportable substations.

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100

Glanded Cable

OP th

th Pilot (Optional)

OP

OP EL ZM

EL

BARR

Z

OP

FC

OP OP

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(a) Eq u i p m e nt w i t h o u tg o i n g g l a n d e d s e c o n d a r y c a b l e s s u p p l y i n g f i xe d o r t r a n s p o r t a b l e e q u i p m e nt

Incoming and through feed te r m i n a t i o n s m a y be plugged or glanded

B o l te d A d a p te r

OP th

th Pilot (Optional)

OP

OP EL ZM

EL

BARR

Z

OP

FC OP

PEC

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( b) Eq u ip m e nt s u b s t ati o n wi th b o l te d a d a pte r s s u p p l y i n g f i xe d o r tr a n s p o r t a b l e e q u ip m e nt wi th o pti o n a l e a r th c o nti n u i t y p r ote c ti o n

OP Incoming and through feed te r m i n a t i o n s may be plugged or glanded

OP th EL OP EL ZM

Restrained Receptacle

th EFL

Z

OP

BARR

FC Pilot PEC

(c) Eq u i p m e nt s u b s t a ti o n w i t h o u tg o i n g s e c o n d a r y r e c e pt a c l e s s u p p l y i n g m o b i l e m a c h i n e d i r e c t L EG EN D: th

O ve r l o a d p r o te c t i o n

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S h o r t- c i r c u i t p r o te c t i o n EL EFL FC

ZM

C o r e b a l a n c e E / F p r o te c t i o n

C u r r e n t l i m i t i n g r e s i s to r o r r e a c to r

PEC

Pi l o t e a r t h c o n t i n u i t y p r o te c t i o n

BARR

Ze n e r b a r r i e r o r r e s i s t i ve b a r r i e r

E a r t h f a u l t l o c ko u t

OR

Ei t h e r o n e of t h e o t h e r c o n n e c te d i te m s m ay b e u s e d

Fr oze n c o n t a c t o r L o s s of va c u u m p r o te c t i o n

OP

This operation optional

C i r c u i t- b r e a ke r

C o n t a c to r

Ear th facility

I n te r l o c k

N E R m o n i to r

FIGURE B1 PROTECTION ARRANGEMENTS

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B4 TESTING OF POWER SYSTEM PROTECTION SYSTEM All equipment is subject to gradual degradation with time, including power system protection equipment. Therefore, a regular inspection and testing regime has to be provided to identify the equipment concerned so that remedial action can be taken before scheme maloperation occurs. This is particularly the case for older electromechanical relays, for which a minimum annual test regime should be implemented.

With digital and numerical relays, the in-built self-testing routines can be expected to reveal and annunciate most faults, but this does not cover any other components that, together, comprise the protection scheme. Therefore, regular review of protection settings is also required, in order to minimize the possibility of incorrect settings. This is particularly the case as site fault levels may change over time, and hence setting calculations may need to be revised.

The frequency of periodic verification of an installation should be based on the type of installation and equipment, its use and operation, the frequency and quality of maintenance and the external influences to which it is subjected.

B4.1 Electromechanical relays

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Annual testing should be conducted per the manufacturerâ&#x20AC;&#x2122;s instructions. Such tests may include the following: (a)

Check of the time-current characteristic.

(b)

Check of the minimum operating current.

(c)

Examination of magnetic air gaps for dirt.

(d)

Examination of bearings for dirt.

(e)

Cleaning of contacts and drawout contact fingers.

(f)

Replacement of dust filters if fitted.

(g)

Check of settings.

B4.2 Digital and numerical relays A maximum period of five yearly testing should be conducted or as per the manufacturerâ&#x20AC;&#x2122;s instructions. Such tests may include the following: (a)

Single-phase secondary current injection.

(b)

Three-phase secondary current injection.

(c)

Check of settings.

(d)

Relay self-test procedure if available.

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APPENDIX C

GUIDELINES FOR LOW SIGNAL LEVEL SYSTEMS AND COMMUNICATION SYSTEMS (Informative) C1 INTRODUCTION This Appendix sets out guiding principles for low signal level systems (for transmitting measured values, control data, control instructions, etc.) and communication systems (for transmitting speech, sounds, pictures, characters, etc.) in order to protect persons and property againstâ&#x20AC;&#x201D; (a)

the transfer of unsafe voltages from power systems or other circuits; and

(b)

malfunctions due to interference originating either from within the system or from an external influence such as nearby OHLs, radio transmitters or heavy electrical equipment.

It applies to the installation of low signal level systems and communication systems in the locations covered by this Standard. These systems have to comply with the relevant requirements of this Standard.

This Appendix does not apply to railway signalling systems.

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C2 ASSESSMENT OF GENERAL CHARACTERISTICS An assessment should be made of the following characteristics of the installation: (a)

Means of transmission, for example, cable, powerline carrier, radio or optical systems.

(b)

Signal type, e.g. analogue or digital.

(c)

Interference to signal transmission by power supplies (e.g. harmonics, voltage transients), other circuits, lightning, and radio signals, etc.

(d)

Interference by indirect transfer of voltage, e.g. inductive (electromagnetic), capacitive (electrostatic), resistive (ohmic), galvanic (electrolytic).

(e)

Interference by direct transfer of voltage from power systems.

(f)

Interference from fault current in the earthing system influencing the reference potential.

(g)

Power supply for the low signal level system and communication system, including regulation of voltage, current and frequency, effects of fault current, effects of harmonics, maintenance of potential reference for the system, effects of loss of power.

These characteristics should be taken into account in the choice of methods of protection to ensure safety of persons and to avoid malfunction of equipment.

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C3 PROTECTION OF PERSONS AGAINST THE TRANSFER OF UNSAFE VOLTAGES C3.1 Causes of voltage transfer Unsafe voltages may be transferred to low signal level systems and communication systems byâ&#x20AC;&#x201D; (a)

direct transfer of voltages due to insulation failure, mechanical damage, accidental contact, leakage between adjacent terminals, or failure of equipment; and

(b)

indirect transfer of voltages resulting from inductive and capacitive coupling with other circuits.

C3.2 Measures for protecting persons against direct transfer of unsafe voltages

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One or more of the measures described in Items (a) to (k) below should be adopted. There may be other measures that provide equivalent protection. Not all of the measures listed are effective for all types of TN, TT and IT systems described in this Standard. (a)

Use of SELV for the power system.

(b)

Use of cables in the power system with metallic screens and/or armouring.

(c)

Use of cables in the power system with semi-conducting layers.

(d)

Use of cables in the power system with double insulation or reinforced insulation.

(e)

Inclusion of all exposed conductive parts of the low signal level system or communication system, which may become live in the event of a fault in the power system, in the protective measures against indirect contact of the power system.

(f)

Application of conductive shielding between conductors of the low signal level system or communication system and conductors of other circuits. The shielding should be connected to a protective conductor and sized in accordance with the prospective fault current.

(g)

Use of isolating transformers or optical isolators to terminate the conductors of low signal level systems or communication systems for the purpose of providing isolation from other circuits.

(h)

Installation of cables of low signal level systems or communication systems physically separate throughout their entire length from other cables, with or without the use of barriers. Terminals should be grouped physically separate from terminals of other systems and, if necessary, provided with barriers, shrouds, etc.

(i)

Use of cables provided with either armouring and/or double insulation or reinforced insulation for the circuits of low signal level systems and communication systems.

(j)

Use of fuses and/or over-voltage protection equipment for each conductor of low signal level systems or communication systems.

(k)

Use of Class II equipment for low signal level systems or communication systems.

NOTE: Class II equipment is equipment in which protection against electric shock does not rely on basic insulation only, but in which additional safety precautions, such as double insulation or reinforced insulation, are provided, there being no provision for protective earthing or reliance upon installation conditions.

C3.3 Measures for protecting persons against indirect transfer of unsafe voltages One or more of the following measures should be adopted (or other measures that provide equivalent protection): (a)

Use of isolating transformers or optical isolators to terminate the conductors of low signal level systems or communication systems for the purpose of providing isolation from other circuits.

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Use of fuses and/or overvoltage protection equipment for each conductor of the low signal level system or communication system.

The above measures need not be taken if it is determined by calculation or measurement that the magnitude and the characteristics of the transferred voltage will not present a hazard.

C4 PROTECTION OF LOW SIGNAL MALFUNCTION DUE TO INTERFERENCE

LEVEL

SYSTEMS

AGAINST

C4.1 Basic principle Where electrical interference could cause malfunctioning and result in a condition dangerous to persons, or property, measures should be taken to reduce the effect of the interference to an acceptable level. Examples of the measures which can be taken are given in Paragraphs C4.2 to C4.4. A combination of these measures may be required.

C4.2 Protection measures C4.2.1 Design features

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Design features which may be incorporated in the equipment to reduce its susceptibility to interference include the following: (a)

Common mode rejection.

(b)

Propagation delay methods at input interface.

(c)

Majority logic.

(d)

Feedback supervision.

(e)

Cross-monitoring techniques.

(f)

Circuit isolation (for example optical isolators, isolating transformers).

(g)

Coding of signals, parity checks, etc.

(h)

Overvoltage protection equipment.

(i)

Use of Class II equipment.

(j)

Use of cables with double insulation or reinforced insulation.

C4.2.2 Other measures Other measures which may be taken to minimize the effects of interference include the following: (a)

Screening against capacitive (electrostatic) interference.

(b)

Shielding against inductive (electromagnetic) interference.

(c)

Physical separation of cables.

(d)

Segregation of circuits.

(e)

Physical isolation of sensitive components.

(f)

Suppression of interference at source, e.g. of harmonics, voltage transients.

(g)

Use of higher signal levels or signal amplification.

(h)

Use of line fuses.

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C4.3 Transmission by cable C4.3.1 Screening against capacitive (electrostatic) interference Screening of cables by means of conductive materials may be used to eliminate or minimize capacitive interference. The screening should extend over the length of the cable and should be taken as close as practicable to the cable terminations.

The screen should be insulated from earth along its entire length and left unearthed or connected directly at one location only with the lowest practicable impedance to the low signal level system common earthing point or zero potential common reference point.

Cable armouring, conduit or cable tray, if constructed of materials having good electrical conductivity and installed as described above, can provide a measure of screening from capacitive interference, but will be less effective than the use of cables incorporating screens designed specifically for the purpose.

The connection of spare cores in a cable to earth or to the common reference potential at the receiving end will also afford a limited measure of screening against capacitive interference, provided the spare cores are connected as described above for a cable screen.

Extremely sensitive low signal level systems may require the use of cables incorporating screening for each signal circuit pair in addition to the overall screening of the cable.

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C4.3.2 Shielding against inductive (electromagnetic) interference Interference arising from inductive coupling may be minimized by keeping the area enveloped by the circuit as small as possible, for example, when signal-carrying conductors run alongside the conductor serving as the common return or reference potential conductor.

The most effective shielding against inductive interference is achieved by twisting a conductor serving as the common reference potential with each signal-carrying conductor in a multicore twisted pair cable. This measure minimizes inductive interference from other cables and from other conductors incorporated in the cable.

Shielding of cables by means of ferrous materials (e.g. steel conduits, steel cable trays, steel cable armouring) may be used to minimize electromagnetic coupling with other cables.

The effectiveness of the shielding will generally be reduced where bonded to adjacent earthed metallic parts, or where it is impracticable to maintain the insulation of the shielding over its entire length.

The effectiveness of cable trays and cable armouring as shielding depends on the construction and method of earthing. Generally, cable tray and armouring is significantly less effective than steel conduit enveloping the entire cable. Conduits and cable trays should be solidly connected and bonded, where necessary, to bridge any discontinuities and in order to maintain electrical continuity throughout their entire length.

C4.3.3 Physical separation from power cables and equipment Where cables of low signal level systems are run in parallel with power cables (or busbar systems), or in close proximity to equipment producing external variable magnetic fields, it may be necessary to separate the signal cables from the power cables with or without metallic barriers or equipment to minimize interference. This applies particularly where the signal cables are not screened or shielded.

The question of whether separation is required and the degree of separation which might be necessary will depend on factors such as the type of cables used (both signal and power cables); the signal level employed, the distance over which the signal cables are run in parallel with the power cables, and the maximum expected current in the power cables (e.g. motor starting current, power cable fault current).

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C4.3.4 Segregation of circuits Circuits having widely different current or voltage levels should be run in separate cables or cable looms, particularly if none of the measures described in Paragraphs C4.3.1 to C4.3.3 are taken.

C4.3.5 Transmission by powerline carrier For powerline carrier systems, see IEC 60353, IEC 60481, IEC 60495 and IEC/TR 60663.

C4.4 Transmission by radio C4.4.1 Safety precautions relating to the use of radio Precautions should be taken to prevent accidental ignition of detonators. Guidance on the prevention of inadvertent initiation of electro-explosive devices by radiofrequency radiation is provided in BS 6657.

Precautions should be taken to prevent unintended operation of radio remote-controlled equipment. Guidance on the prevention of unintended operation of radio remote-controlled equipment is provided in AS/NZS 4240.

C4.4.2 Physical isolation of sensitive elements

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Equipment of low signal level systems may be enclosed separately from power equipment (e.g. transformers, switchgear, etc.) in enclosures constructed of ferrous material (e.g. steel cabinets, cubicles), so as to provide effective shielding from likely sources of interference.

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APPENDIX D

VARIABLE SPEED DRIVES (Informative) Variable speed drive (VSD) systems have a different range of operation than that expected, with motor drives running at relatively constant speed and on 50 Hz sinusoidal supply. The operation of the VSD is normally across a wide range of applied motor voltage and frequency in order to vary the motor speed and torque. These different operating conditions may create increased levels or new types of risk not covered by the traditional protection measures covered elsewhere in this Standard.

With the rapidly changing range of technologies, switching devices and operating conditions of use, it is not possible to specify in this Standard all possible risks and control measures. Manufacturers and users of these technologies should consider the differences that may create additional or new hazards, e.g. changing operating power supply frequency, high frequency switching harmonics, power segregation and common mode voltages between incoming and outgoing VSD circuits.

Before installing any VSD, the operators of mines should review the manufacturerâ&#x20AC;&#x2122;s recommendations for the safe use of this equipment to make sure the device is used within its safe limits.

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VSD should comply with IEC 61800-5-1 and IEC 61800-5-2. Cables supplying variable speed drive motors should be selected in accordance with the drive manufacturerâ&#x20AC;&#x2122;s recommendations.

NOTE: Where EMC compliant cables are unavailable, the use of steel wire armoured cables may be considered in consultation with the drive manufacturer.

Table D1 provides a list of possible risks and guidance notes. This list is not exhaustive, but is a reference list of the typical range of possible risks that need to be considered with any VSD system when complying with this Standard.

Undesirable outcomes may exist where an inappropriate combination is used or where one component is not compatible with the application.

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TABLE D1 VARIABLE SPEED DRIVEâ&#x20AC;&#x201D;GUIDANCE FOR IDENTIFICATION OF POTENTIAL RISKS Potential risks Most LV VSDs have non-sinusoidal voltage outputs which produce continuous circulating high frequency common mode currents

Where a VSD has a non-sinusoidal output produced by pulse with modulated voltage pulses, reflections on the motor cables can produce voltage spikes at up to twice the line voltage

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Transformer coupling within VSD motor causing bearing failure

Temperature rise of motor due to VSD characteristics

Overheating of VSD enclosure

Possible guidance 1

Additional high frequency earth bonding between the frames of the drive, motor and gearbox is advised.

2

The thermal rating of motor supply cables needs to allow for the circulating current component.

3

Before using VSD supplied motors in hazardous areas, the effect of these circulating currents needs to be considered.

(Refer to AS/NZS 4871.1.)

4

The higher the carrier frequency of the VSD drive, the higher the circulating current component.

1

Consideration needs to be given as to whether a motor supplied from a VSD should be manufactured with form wound windings to withstand the voltage spikes produced by some VSD drives.

2

The use of purpose-built terminators (filters) to suppress voltage reflections or resonance should be considered in applications with long motor leads. The failure modes and the effect of such failures should be understood for these filters.

1

Consideration needs to be given as to whether a motor supplied from a VSD should be manufactured with an insulated bearing on the non-drive end to prevent motor bearing damage.

2

Likewise, consideration needs to be given as to whether an earth brush on the rotor shaft of a VSD fed motor would reduce bearing damage in the associated gearbox.

Consideration needs to be given to the thermal capacity and protection of a motor supplied from a VSD with respect to the following: 1

Carrier frequency: the lower the frequency, the higher the harmonic heating in the motor.

2

Incorrect software management of the VSD could lead to over-fluxing of the motor at low speeds.

3

Supplementary cooling may be required for air-cooled motors running for extended periods of time at low speeds.

1

VSD drives and their associated sine wave filtering equipment (where used) can produce significant heat in switch rooms.

2

The higher the carrier frequency of the VSD, the higher the heat produced by the motor controller.

Inability of earth leakage relays to protect the drive side of a VSD

The current output of a VSD may have fundamental frequencies from 0 to 60 Hz, with repetitive non-sinusoidal high frequency voltages superimposed over that output. Where the control of touch and step potentials depends in part on an earth leakage relay, the designer needs to consider whether such a relay is suitable for this application. Type B relays should also be taken into consideration, to enable the d.c. capacitor to be included in such protection.

Filter capacitance storing charge

Failure of discharge resistance reveals fault.

Bus capacitor: residual charge

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TABLE D1 (continued)

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Potential risks

Possible guidance

Failure of protection due to high frequency or d.c. components

Toroids may not suitable for d.c. or high frequency detection.

Filters may be exposed to full line volts during an earth fault when connected on an IT system

All filters should be rated line voltage on IT systems.

Rising step and touch potential across earthing conductors due to circulating and charging currents

When calculating the touch and step potential between a VSD drive and motor, the circulating and charging currents have to take into consideration the following: 1

In an installation with a single VSD controller and drive, the installation of an EMI filter at the drive significantly reduces circulating currents between the supply and drive.

2

Where multiple VSD drives and motors are installed, the EMI filters can add significantly to the charging current between the various drives. This issue is most prevalent on high impedance earthed systems where high frequency charging current between the EMI filters can greatly exceed the NER let through current.

Partial failure of filter (e.g., one/two phases of three-phase filter will increase circulating currents)

Faults should be self-revealing.

Voltage harmonics induced back into the supply system

Refer to the AS/NZS 61000 series and AS 61800.3.

Switching a VSD output while it is running may result in potential VSD component failure

1

Control isolation prior to output isolation.

2

A VSD controller should not be considered acceptable as an isolation device for protection against electric shock.

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APPENDIX E

DOCUMENTATION (Informative) E1 SAFETY FILE

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The following is a list of topics that should be considered in the preparation and ongoing management of all electrical plant: (a)

Ownership.

(b)

Design limits and conditions of safe use.

(c)

Parts book.

(d)

Technical documents on components.

(e)

Design risk assessments.

(f)

Design changes, including updates to the strategic earthing plan (refer to Appendix F).

(g)

Manufacturersâ&#x20AC;&#x2122; test reports.

(h)

AS/NZS 3007 compliance audit.

(i)

Applicable Standards compliance audits as agreed between supplier and user or where legislated.

(j)

Voltage, frequency and power ratings.

(k)

IP ratings.

(l)

Safety requirement specifications (identification of all safety functions and associated safety integrity requirements and PES safety assessments).

(m)

Arc fault containment.

(n)

Pre-delivery inspection.

(o)

Electrical schematics.

(p)

Regulatory correspondence and safety alerts.

(q)

OEM safety alerts.

(r)

Fault level and protection settings.

(s)

Site commissioning.

(t)

Training.

(u)

Installation instructions.

(v)

Isolation.

(w)

Operational risk assessment.

(x)

OEM maintenance schedule.

(y)

Mine site maintenance schedule.

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AS/NZS 3007:2013

Overhaul/test documentation as follows: (i)

Maintenance records.

(ii)

Safe working procedures.

(iii) Commercial standards. (iv)

Chemicals.

(v)

Stored energy.

(vi)

Asset register.

(vii) Method of disposition.

For hazardous areas equipment refer to AS/NZS 60079.14, AS/NZS 60079.17 and AS/NZS 3800.1.1.

E2 PROPRIETORY INFORMATION Information necessary for the safe use of the equipment over the life cycle should be made available for use by the operator.

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Where information is considered proprietary, special arrangements should be made between parties involved.

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APPENDIX F

EARTHING (Normative) F1 INTRODUCTION F1.1 General This Appendix provides earthing requirements.

NOTE: This Appendix will be deleted by amendment when AS 2067 has been revised to incorporate mine earthing.

These requirements supplement the requirements of AS/NZS 3000, AS 2067, AS 60204.1 and AS 60204.11.

F1.2 Objectives

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The objectives of earthing of electrical installations are— (a)

to provide a sufficiently secure low impedance path to allow circuit protection to operate when required to clear faults resulting from an insulation failure to earth;

(b)

to limit touch voltages, transfer potentials and step voltages to a level that is not dangerous (this is often termed ‘protection against indirect contact’);

(c)

to provide overvoltage protection and voltage stabilization; and

(d)

to provide dissipation of electrostatic charge.

F1.3 Risk management treatment methods When designing earthing systems, the following treatment methods may be considered when assessing how best to manage the risk associated with step, touch and transferred voltage hazards: (a)

Reduction of the impedance of the earthing system.

(b)

Reduction of earth fault current.

(c)

Reduction of the fault clearing times.

(d)

Surface insulating layer.

(e)

Installation of gradient control conductors.

(f)

Separation of HV and LV earth electrodes.

(g)

Combined HV and LV earth electrodes.

(h)

Isolation.

(i)

Coincidence reduction (for example, protective barriers, signs).

(j)

Relocation of non-compliance infrastructure (for example, Telco pits).

F1.4 Risk management additional approaches Maximum touch voltage/clearance time performance criteria are specified in Clause 2.4. If compliance with these performance criteria is met but is not sufficient to meet the mine’s acceptable risk level, one of the following additional approaches may be taken: (a)

More conservative touch voltage/clearance times may be adopted (refer to Paragraph F5 for criteria).

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(b)

Additional risk controls (e.g. limiting access, lumped impedance, use of non-conductive materials).

(c)

Creation of applicable touch voltage time curves (see AS 2067).

(d)

A risk-based engineered approach may be used (see ENA EG0).

F1.5 Risk management of transferred touch voltages F1.5.1 General Transfer voltages can be an issue for underground mine distribution systems, trailing cable fed mobile mining machinery (surface and underground), and wet areas frequented by large groups (e.g. bath houses). Transfer voltages shall not give rise to touch voltages in excess of those specified in Clause 2.4.

F1.5.2 Risk management of transferred touch voltages using impedance earthed IT systems Impedance earthed IT systems applied to HV installations offer considerable benefits in the safe management of voltages developed during earth faults (see Paragraph A5, Appendix A.)

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The selection of the required impedance requires the balancing of requirements for compliance, adopting consistent site practices across an installation and allowing for future expansion requirements. Table F1 gives typical values of impedances that are currently used in IT systems.

Due to the particularly unique hazards in underground workings of a mine and trailing cable fed mobile machinery, historically preferred earth fault current limitation levels at various voltages have been adopted. The use of these preferred values does not guarantee compliance.

TABLE F1 PREFERRED EARTH FAULT CURRENT LIMITATION CURRENTS System voltage kV

Earth fault current limitation A

Impedance Ί

66

200

190

33

180

106

22

25

508

11

25 or 10

254 or 635

6.6

25 or 10

152 or 381

3.3

5

381

NOTES: 1

The selection of earth fault current limitation devices, whether resistors, reactors, resonant or other combination, have to be supported by appropriate engineering processes, taking into consideration earth fault current limitation, inherent robustness, equipment failure modes and switching overvoltages.

2

Resistive earth fault current limitation devices are preferred in that system over-voltages and peak touch voltages can be minimized due to the minimal inductive reactance of resistive earth fault current limitation devices.

3

The type of earth fault current limitation device should be selected when determining the earthing philosophy for the mine. For existing installations that use reactive earth fault current limitation devices any change to the use of resistive devices should be subject to engineering analysis.

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F2 EARTHING DESIGN, MANAGEMENT AND INTEGRATION The earthing design should be coordinated with the civil design. For mines with significant HV reticulation on site, a strategic mine earthing plan should be implemented and includeâ&#x20AC;&#x201D; (a)

the philosophy of the earthing system and how the risk is to be managed;

(b)

incoming supplies to the mine;

(c)

separations required;

(d)

interconnections and interrelationships;

(e)

coordination of earthing and electrical protection strategies;

(f)

life cycle management; and

(g)

drawings and documentation that describe the earthing system and records of all test results.

At the earthing design phase, the following information should be communicated to the earthing system designers: (i)

Supply earth fault current limitation and protection characteristics (these are key measures of the hazard magnitude).

(ii)

Soil resistivity and model (layering), which are parameters that affect voltage transfer and step/touch voltages.

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(iii) Performance criteria for the earthing system. (iv)

Location of the main substation (point of connection to the network service provider).

(v)

Area required by main substation.

(vi)

Primary equipment selection.

(vii) Separate or combined earthing system. (viii) Location of bore holes, drifts, shafts, underground conveyors, overland conveyors and OHLs (induction from OHLs into other structures above and below ground). (ix)

Location of other services, e.g. air and water piping.

(x)

Consideration of life-cycle management of earthing systems (see AS 2067).

F3 UNDERGROUND MINES (COAL AND METALS) There is potential benefit for electrical supplies entering underground being impedance earthed systems, as they readily control touch and transfer potential.

For underground mines, there are additional risks to indirect contact issues that should be taken into consideration, specifically the risk associated with energy transfer to underground working/s, in particularâ&#x20AC;&#x201D; (a)

lightning (with lightning strikes you have no control over where and when it will occur, nor the energy levels that lightning produces);

(b)

conduction of fault current from the network service provider (this is generally not an issue with impedance earthed IT systems where the earth systems are separated due to the low level of current transferred); and

(c)

inductively coupled energy transfer from OHLs/communication services/microwave dishes.

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Where there is no likelihood of transferring the effects of lightning into underground mines, lightning protection should be in accordance with AS/NZS 1768. Where transferring lightning underground is identified as a risk, the following principles should be applied: (i)

No direct connection of the lightning protection earth to the underground mine earthing system.

(ii)

Supplementary bonding underground in accordance with the principles of AS/NZS 1768.

(iii) Minimizing the lightning collection area. (iv)

Adequate insulation between separate earthing systems.

(v)

Reducing earth connection resistances.

If applied properly these principles can mitigate the effects of lightning at high risk locations of mining working faces (where shot firing or potentially explosive atmospheres are likely to occur and where touch voltage issues are likely to be increased due to the environment).

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Lightning energy can be transferred from the incoming supply overhead line to the underground mine supply through surge diverters connected between the incoming supply and the network earth (NE). Separation of the mine underground earth (MUE) and the NE can contribute in preventing this transfer of energy. If the mine earth is sufficiently separated in the ground and air, with no conductive connection, then the lightning energy connected to the underground electricity supply system may be reduced. The decision to separate has to be deliberate and managed for the life cycle of the power distribution system.

All earthing system separations shall be properly designed, installed, commissioned and managed. This is particularly important for protecting MUEs from sources of lightning such as NEs and lightning protection earths (LPEs). Useful in the control of this separation is the concept of â&#x20AC;&#x2DC;buffer zonesâ&#x20AC;&#x2122; (an earthing isolation zone or sterile zone where no earth system may pass into or through). Conductive equipment around buffer zones should be managed to prevent inadvertent interconnection of separated earthing systems. Consideration should also be given to limiting access and activity in buffer zones.

Any mine earth can be either located to minimize the risk of a direct lightning strike or shielded in accordance with AS/NZS 1768. Separation distances between the underground mine earth and the lightning protection earth shall be maintained. In the past, separation distances were specified as 3 m in air and 15 m in the ground; however, consideration should be given to the specific conditions at the mine site.

Other matters that should be taken into consideration areâ&#x20AC;&#x201D; (A)

length and security of the earthing cable route;

(B)

regular/continuous proof testing of earth system; and

(C)

working on underground distribution systems (lightning and point of attachment of working earths).

F4 UNDERGROUND COAL MINES For supplies entering the underground mine workings where there is a potentially explosive atmosphere, an impedance earthed IT system with an appropriate level of earth fault current limitation shall be used.

NOTE: Such systems touch voltages, transfer voltages and step voltages are readily controlled, the energy available in a phase-to-earth arc flash/blast is significantly reduced and, in conjunction with sensitive earth leakage protection, can reduce the coincidence of ignition source and a potentially explosive atmosphere.

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The transfer of lightning energy into the underground workings of coal mines is a known source of mine explosions. Underground coal mines have winder shafts and boreholes for various services that can be a source of transferring lightning energy into a potentially explosive atmosphere. Generally with these types of features it will be necessary to discharge the effects of lightning before it gets to the potentially explosive atmosphere and/or isolate the bore casings and winder shaft conductive structures from conductive structures that may enter a potentially explosive atmosphere.

NOTE: For further guidance on lightning protection systems (LPSs) for underground coal mines, see AS/NZS 1768.

Borehole casings should be non-conductive. Where this is not possible shunt attenuation should be as high as possible.

NOTE: Methods that may be used include— (a) bonding to earth regularly; (b) ensuring good continuity to earth; (c) using conductive grouting; and (d) providing an additional path for surge to travel at the bottom of the borehole/casing (e.g. equipotential bonding and earth electrodes).

F5 TOUCH VOLTAGE/OPERATING TIMES

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In some circumstances, the touch voltage clearance time criteria specified in Tables F2 and F3, and Figures F2 and F3 may be used, as follows: (a)

For voltages up to and including 1000 V, Table F2.

(b)

For voltages above 1000 V, Table F3.

(c)

For graphical representations of the requirements of Tables F2 and F3, Figures F2 and F3 respectively.

TABLE F2 PROSPECTIVE TOUCH VOLTAGE/OPERATING TIME CHARACTERISTICS FOR SYSTEMS UP TO AND INCLUDING 1000 V Prospective touch voltage (a.c., r.m.s.)

V

Maximum operating time

≤50 ≥50 75

∞ 5 1

90 110 150

0.5 0.2 0.1

220 280

0.05 0.03

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AS/NZS 3007:2013

TABLE F3 PROSPECTIVE TOUCH VOLTAGE/OPERATING TIME CHARACTERISTICS FOR SYSTEMS ABOVE 1000 V Prospective touch voltage (a.c., r.m.s.)

V

Maximum operating time

≤50 80 120

∞ 5 1

150 180 300

0.5 0.4 0.1

420 550

0.05 0.03

s

M A X I M U M O PER AT I N G T I M E, s

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5.0

1.0

0. 5

0. 2

0.1

0.0 5 0.0 3 0.0 2 10

20

50

8 0 10 0

20 0 3 0 0

50 0

PR O S PECT I V E TO U C H VO LTAG E, V (a .c. r.m.s .)

FIGURE F2 GRAPHICAL REPRESENTATION OF TABLE F2

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20

10

M A X I M U M O PER AT I N G T I M E, s

5.0

1.0

0. 5

0. 2

0.1

0.0 5 0.0 3

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0.0 2 10

20

50

8 0 10 0

20 0 3 0 0

50 0

PR O S PECT I V E TO U C H VO LTAG E, V (a .c. r.m.s .)

FIGURE F3 GRAPHICAL REPRESENTATION OF TABLE F3

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119

NOTES

AS/NZS 3007:2013

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AS/NZS 3007:2013 120

NOTES

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