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NORTHWEST LINEMAN
CURRICULUM EXCERPTS
ELECTRICAL LINEWORKER PROGRAM
ELECTRICAL GRID 1
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Electrical Grid 1
6.1 THE GENERATION PROCESS LEARN MORE
Power Generation lcvid.com/powergen
1:21
One fundamental law of physics states that energy can be converted but it cannot be created or destroyed. In an AC generator, some form of energy is converted to mechanical motion. The mechanical motion is then used to rotate a machine that converts the motion into electrical energy. The resultant electrical energy travels through the electrical system and is again converted at the point of utilization to a form of energy that is useful to the consumer. This last conversion may be made to heat or motion. Examples of heat energy: • Light bulbs • Toasters • Electric ovens Energy in motion is most often seen in electrical motors. Converting motion to electricity is quite simple. If a conductor is passed near a magnet, current will flow if a complete circuit exists. The law of charges states (in part) that like charges repel. If the negative pole of a magnet is passed near a conductor, all of the negatively charged electrons will move away, creating current flow. Conductor Conductor Ma g Ma net gn et
+
+
+
+
+
+
Negative Charge Negative Charge
+ +
+
+
+
+
+
+
Electrons Repelled Electrons Repelled from Negative Charge from Negative Charge
The law of charges also states that opposite charges attract. If the magnet is reversed, the positive pole will attract the negatively charges electrons back toward the magnet.
Conductor Conductor Ma g Ma net gn et
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Positive Charge Positive Charge
+
+
+
+
+
+
+
+
+
+
Electrons Attracted Electrons by PositiveAttracted Charge by Positive Charge
+ + +
+
AC Generation | CHAPTER SIX
The machine that converts mechanical motion into electrical energy does so by spinning a magnet inside of a coil of wire. This spinning magnet causes the opposite poles to alternately pass near a conductor. The electrons will first rush away from the negative pole of the magnet, creating a positive voltage. As the rotation continues, the electrons will rush back toward the positive pole of the magnet, creating a negative voltage. In AC circuits, the terms positive and negative refer to the direction of current flow in a conductor. Although the coils are generally stationary and the magnet is spun, a spinning coil is shown for illustration purposes.
In AC circuits, the terms positive and negative refer to the direction of current flow in a conductor.
If the voltage causes electrons to flow away from the generating source, the voltage is positive. If the voltage causes electrons to flow toward the generating source, the voltage is negative. This is known as polarity.
+
Positive Voltage
+
Negative Voltage
The strength of the voltage to be produced depends on three factors. These factors are: • The number of turns in the coil of wire • The strength of the magnetic field • The speed at which the magnetic lines of flux pass through the coil
In order for a generator to produce one volt, a single conductor must pass through 100,000,000 lines of flux in one second. If the conductor is doubled and spun at the same rate, two volts would be produced. If we continue to coil the conductor, we will achieve a higher voltage even though the speed and strength of the magnetic field remain constant.
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ELECTRICAL LINEWORKER PROGRAM
METERING
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Metering
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Voltmeter Method 1.
Using a standard voltmeter, the meter base can be checked for back feed, short circuits, open circuit, or closed customer breaker.
With the source side energized and the customer’s disconnect open, proper voltage to the meter socket can be confirmed with the following:
Meter Testing and Installation
• A voltage reading of 120 volts between S1 and neutral; • A voltage reading of 120 volts between S2 and neutral; and
lcvid.com/mtsn
• A voltage reading of 240 volts should be read between S1 and S2
S1
Energized Source (Line)
S1
S2
120 A V
V
V
OFF
Customer Disconnect Open
V
Customer Disconnect Open Load L1
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S2
240
A
OFF
Energized Source (Line)
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Load L2
L1
L2
Self-Contained Meters | CHAPTER ONE
2. With the customer’s disconnect open, a voltage reading of zero between L1 and L2 and the neutral will confirm that the service is not back fed from another source.
S1
Source (Line)
S2
zero reading
0 A V OFF
V
Customer Disconnect Open Load L1
L2
Testing for back feed
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ELECTRICAL LINEWORKER PROGRAM
OSHA FOR POWER DELIVERY
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OSHA for Power Delivery
8,500 ft P-G MAD = 3.85’ P-P MAD = 4.61’ 6,500 ft P-G MAD = 3.65’ P-P MAD = 4.37’ 4,500 ft P-G MAD = 3.45’ P-P MAD = 4.14’
Altitude
Correction Factor
ft
m
3000
900
1.00
4000
1200
1.02
5000
1500
1.05
6000
1800
1.08
7000
2100
1.11
8000
2400
1.14
9000
2700
1.17
10000
3000
1.20
12000
3600
1.25
14000
4200
1.30
16000
4800
1.35
18000
5400
1.39
20000
6000
1.44
Footnote: If the work is performed at elevations greater than 3000 ft (900 m) above mean sea level, the minimum approach distance shall be determined by multiplying the applicable distance from the OSHA Minimum Approach Distance tables by the correction factor corresponding to the altitude at which work is performed.
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2,500 ft P-G MAD = 3.29’ P-P MAD = 3.94’
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Sea Level P-G MAD = 3.29’ P-P MAD = 3.94’
The minimum approach distance on this 69 kV circuit increases with altitude. P-G MAD = Phase-to-Ground Minimum Approach Distance P-P MAD = Phase-to-Phase Minimum Approach Distance
Table R-5
Focus Four | CHAPTER TWO
It’s a requirement by OSHA to know and apply minimum approach distances for the voltages to be worked. However, many companies have incorporated such industry best practices as “extended-reach” rules and “cradle-to-cradle” rules to answer the question, “How close am I to that exposed energized part?” “Cradle to cradle” refers to the wearing of properly rated rubber insulating gloves and sleeves when using an aerial lift. Gloves and sleeves must be worn from the time the aerial basket leaves the cradle to its return. The extended-reach rule requires employees to wear properly rated rubber insulating gloves and sleeves any time they are within 5 feet of energized conductors or holding a conductive object within 5 feet of energized conductors and/or equipment. Methods like these enhance the workers’ safety when performing energized distribution work. Minimum approach distances for systems operating at 72.6kV or higher are much more complex than for the lower voltages. The formula for calculating the distances requires employers to determine the transient overvoltage conditions of the circuits and incorporate those factors into the formulas to ensure the minimum approach distances are adequate for worker safety. Transient overvoltage is a temporary voltage-peak condition on a circuit in which the voltage can reach levels too high for insulation. There are natural causes like lightning and static charges, but these spikes also can result from electrical equipment and switching surges causing the voltage to temporarily exceed the insulation used on the circuit. Spark gaps and surge protectors are typically installed to reduce damage to insulators. Since air is the insulating medium for minimum approach distances, maximum transient overvoltage must be accounted for in determining the correct MAD for the circuit to be worked.
Transient overvoltage is a temporary voltagepeak condition on a circuit in which the voltage can reach levels too high for insulation.
To account for transient overvoltage, employers must perform an engineering study on the particular circuit to be worked, or rely on the values provided in Tables V-8 and R-9, Assumed Maximum Per-Unit Transient Overvoltage. In some cases, the alternative distances in Tables V-6 and R-7 exceed the distances of the insulators used on the circuits. For example, an insulator supporting a conductor on a 345kV circuit can be 8.5 feet to 10.5 feet in length. The alternative phase-to-ground MAD for 345kV in Table V-6 is 11.19 feet at altitudes of up to 3,000 feet above sea level. For this reason, OSHA encourages employers to use the formulas, which can lower the minimum approach distances in certain conditions. For systems operating at 72.6kV and higher, line owners can: • Rely on the alternative distances in Tables V-6 and R-7; • Combine an engineering study of the circuit with the formulas in Tables V2 and R-3 to calculate the customized minimum approach distance; or • Use the MAD calculator on OSHA’s website. OSHA’s minimum approach-distance calculator can be accessed at the following link: www.osha.gov/dsg/mad_calculator/mad_calculator.html NORTHWEST LINEMAN COLLEGE
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Circuit Breakers
CURRICULUM EXCERPTS
CIRCUIT BREAKERS
1.1 INTRODUCTION Circuit breakers control the flow of power on the system by energizing and de-energizing lines and equipment. They are a critical piece of equipment in the substation. When needed, circuit breakers interrupt fault current flow and isolate faulted sections of the system. They must be capable of closing into a fault. Circuit breakers must be properly designed, properly maintained and tested, and very reliable. Circuit breakers work in conjunction with relays. Settings can be coordinated with other devices to meet system conditions. Circuit breakers can be operated manually at the breaker, remotely in the control building or at the operations center. There are three key specifications for selecting circuit breakers for installation: 1. The continuous load current that the breaker must carry under normal and emergency conditions. 2. The level of fault current that the breaker must be capable of interrupting. 3. The speed of the fault current interruption. The system must have circuit breakers able to interrupt faults as rapidly as possible. The rapid clearing of faults reduces the chances of extensive damage or fire.
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Substation breakers trip all three phases during operations, though some transmission systems will install single pole tripping on breakers so that power can still be delivered on the other two phases when a phase to ground fault is experienced. Single pole tripping can improve the stability of the transmission system. Circuit breakers are also selected based on economics, and the type of breakers available for the voltage level being considered. The advantages and disadvantages of the interruption methods (such as oil or vacuum) are also thoroughly evaluated.
1. 2. 3. 4.
OCB – Oil Circuit Breaker PCP – Power Circuit Breaker Circuit Switcher Transrupter
CHAPTER ONE | INTRODUCTION TO CIRCUIT BREAKERS
The following is a list of common names for devices that perform the basic function of a circuit breaker:
Bushing
Tank Dome
Crank Box Capacitance Tap Oil Gauge Current Transformer
Tank Upper Static Shield
Lift Rod Guide Guide Block
Lift Rod Interrupter
Contact Button
Lower Static Shield
Cross Arm Drain Valve
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Manhole
Oil circuit breaker.
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Electrical Test Equipment
CURRICULUM EXCERPTS
ELECTRICAL TEST EQUIPMENT
Testing Voltage
When reading voltage, all possible voltage combinations are checked.
Lineworkers most commonly use multimeters to read AC voltage. This should occur after every transformer installation to prove that the required voltage is supplied to the customer. It also confirms that the transformer is connected correctly to the system primaries and the customer’s service. When reading voltage, all possible voltage combinations are checked. On a 120/240-volt, single-phase service, three readings would be checked at the meter panel or at the transformer: hot leg 1 to neutral, hot leg 1 to hot leg 2, and hot leg 2 to neutral.
HL 1 N
HL 2
HL 1 N
HL 2
HL 1 N
HL 2
Always confirm that the meter is set to the proper voltage range.
120 OFF
240
V
OFF
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Hot Leg 1 to Neutral
Notice that this meter is rated for a maximum voltage of 1,000 volts DC and 750 volts AC.
120
V
OFF
Hot Leg 1 to Hot Leg 2
V
Hot Leg 2 to Neutral
Multimeters have a voltage limit that should never be exceeded. Severe injury and equipment damage can occur if a multimeter is used for a higher voltage than it is rated for. Always confirm that the meter is set to the proper voltage range for the given circuit.
1:52
Testing Continuity Multimeters are usually equipped with a continuity test function. Continuity ensures that a conductor is not broken, or that the conductor is continuous.
Transformer Continuity lcvid.com/transcont
An audible sound should not be heard between the primary and secondary windings of a transformer.
The multi-tester will give off an audible sound when the two probes contact one another, either directly or through a conductive object. This feature is especially useful when proving the integrity of transformer coils. Knowing that the primary coil should be connected between the H1 and the H2, an audible sound will be heard when the probes touch the bushings. The multimeter is now set to continuity. An audible sound will also be heard between all combinations of the secondary bushings. An audible sound should not be heard between the primary and secondary windings of a transformer. If continuity is proven between the primary and secondary coils, the transformer is defective and should not be used.
CHAPTER ONE | LOW-VOLTAGE TEST EQUIPMENT
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When set to continuity test, the multimeter will give off an audible tone when the probes contact one another.
Some utility companies require a continuity test before transformers, new or rebuilt, are placed in service. Continuity testing transformer coils can also be part of the troubleshooting process when a customer loses power due to a blown fuse. NO TONE
H2
x3
x2
x1
Primary coil continuity
H1
H2
x3
x2
x1
Secondary coil continuity
H1
H2
x3
x2
x1
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H1
Primary to secondary NO continuity
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Live-Line Equipment And Methods
CURRICULUM EXCERPTS
LIVE-LINE EQUIPMENT AND METHODS
Apparel Flame-retardant clothing shall be worn at all times while performing rubber glove procedures. In addition, all jewelry and metal articles shall be removed. Experience has shown that removing metallic articles and wearing flame retardant clothing could have avoided many injuries.
Non-Reclose Condition
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The non-reclose feature should always be actuated for the duration of the rubber glove project. Anatomy of an Arc
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lcvid.com/antarc
A live-line tool should always be used to open or close disconnects if connected to a load.
There are many terms for a nonreclose condition such as non-test, one shot, hot line hold, hold off, etc. Circuit breakers and reclosers should always be set to non-reclose for the duration of the rubber glove project to prevent the line from becoming automatically re-energized should an electrical contact occur.
Connecting or Breaking Load Lineworkers should never open or close disconnects, or any other apparatus, with rubber gloves if the disconnect or apparatus is connected to a load. The potential for a large arc is very high. A live-line tool should always be used to open or close disconnects if connected to a load.
Conductor Control A critical element is to always maintain positive control of the energized conductors. When a conductor is moved, full attention should be placed on the conductor in both directions of the work location. In addition, extra care should be taken to ensure that the conductor is moved slowly and without jerking motions. When a conductor is to be tagged away from the work area with a link stick and tag line, the tag line should be carefully secured to ensure that it does not come loose unintentionally during the project. The anchorage point should be a solid object to guarantee stability. A qualified employee on the ground should be designated to tie and untie the tag lines.
Before starting a rubber glove project, and after proper work area protections (traffic cones, signs, barricading, etc.) have been installed, the following procedures should be followed:
Non-Reclose The protective device on the circuit being worked should be verified as being set to non-reclose.
Work Location Inspection The work location includes the pole being worked and any adjacent poles that may be affected by a change in strain.
The work location includes the pole being worked and any adjacent poles that may be affected by a change in strain.
CHAPTER FOUR | RUBBER GLOVE METHODS
4.4 PRE-JOB PROCEDURES
A thorough inspection of the work location should include, but is not limited to the following: •
Testing the poles for rot, include testing poles adjacent to the work location that may be affected by any change in strain caused by conductor movement.
•
Inspect the length of all conductors for weak points and damage.
•
Inspect arms, pins, ties, brackets, and all other pertinent support hardware at all locations to verify that they can withstand any change in strain caused by conductor movement.
Inspect arms, pins, ties, etc.
Inspect arms, pins, ties, etc.
Test for rot
Work location ations) d and adjacent loc (Pole being worke
Work location inspection
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Test for rot
Inspect conductors
63
Steel Structure Maintenance
CURRICULUM EXCERPTS
STEEL STRUCTURE MAINTENANCE
Any tower component where two pieces of metal are joined and one is stationary while the other one moves will eventually need replacing or fixing.
Insulator support brackets In the photo captioned, Static wire support bracket, the movement of the static wire has caused the nut to fall off, the bolt is backed out and the static wire is in danger of falling. Any tower component where two pieces of metal are joined and one is stationary while the other one moves will eventually need replacing or fixing. In the photo, Vertical insulator string bracket, the tension keeps the nuts on the U-bolt from backing off but the bottom of the U, where the insulator hook rests is subjected to extreme wear.
Static wire support bracket
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The bracket supporting the static wire can be replaced by attaching a Gin-pole to the steel member above the bracket and using a hoist to hold the weight while the bracket is changed out. Since the static wire only has to be lifted enough to relive the pressure, the procedure can be accomplished live-line. When the bracket on the insulator string has to be replaced, the conductor would have to be supported and the insulator string removed.
30
Vertical insulator string bracket
Arm (bridge) replacement
Transmission tower arms are replaced when there is storm damage or the tower is being uprated for more phase clearance. The bridge is replaced using a Gin-pole to lower and raise components or by helicopter. The job is done with the conductors off the tower, and is considered a harder job than inserting a new section into the tower to gain height. It would normally take the five man crew in the photo 1-2 days per tower to change the crossarm.
Chapter Two | Member Replacement
Arm (bridge) replacement
Steel H-frame The conductors and insulators are lowered and protected, then slings or chain hooks are attached at the lifting eyes to lower and raise the crossarm. The steel poles have studs welded on two sides so that workers can install steps as they climb.
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Steel H-frame
31
Substation Communication Systems
CURRICULUM EXCERPTS
SUBSTATION COMMUNICATION SYSTEMS Northwest Lineman College
Modems are commonly used to modulate an analog carrier signal.
SCADA systems are used to control fans and monitor transformer temperatures.
SCADA systems receive current inputs from current transformers.
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This 15 kV circuit breaker is monitored and controlled via SCADA.
te of Electr i
itu
Ins t
IEEE 1379-2000 standard recommends a set of best practices for implementing modern SCADA Master-RTU/IED communication links. The standard references DNP3 as the communications protocol to be considered for SCADA systems. DNP3 (Distributed Network Protocol) is a set of communications protocols used between components in process automation systems. Its main use is in utilities such as electric and water companies. It was developed for communications between various types of data acquisition and control equipment. It plays a crucial role in SCADA systems, where it is used by SCADA Master Stations, Remote Terminal Units (RTUs), and Intelligent Electronic Devices (IEDs). It is primarily used for communications between a master station and RTUs or IEDs. ICCP, the Inter-Control Centre Protocol, is used for inter-master station communications. The DNP3 protocol supports time synchronization with an RTU. The DNP protocol has time stamped variants of all point data objects so that even with infrequent RTU polling, it is still possible to receive enough data to reconstruct a sequence of events of what happened in between the polls. A Remote Terminal Unit for the DNP3 protocol can be a very small, simple embedded device, or it can be a very large, complex rack filled with equipment.
s
IEEE STANDARD 1379-2000 AND DNP3
Engine ics er
IEEE
CHAPTER FOUR | SUBSTATION COMMUNICATION SYSTEMS
l and Electr
on
ca
While this protocol is robust, efficient, compatible, and secure, it is getting more and more complex and subtle as it ages. While this is partly due to more demanding industrial applications, it is also a reflection that SCADA concepts are not as simple as they might first seem. The goal of compatibility is more important than ever, as advancement in use of SCADA for delivering smart grid concepts becomes a reality.
SCADA Master Station/Control Center
Comm. Links
Remote Substation
1200 bps + (down to 300 bps in actual installations)
Intelligent Electronic Devices
Radio Microwave Spread-spectrum
HMI/SCADA Master External Control Points
Twisted-pair Fiber-optics Dial-up Leased Line
Meter
Remote Terminal Unit (RTU)
Accumulator
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Actuator
Programmable Logic Controller (PLC)
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