IEC 61850
THE COMMUNICATIONS PROTOCOL FOR THE ELECTRICAL INDUSTRY FOR TOO LONG, THE ELECTRICAL INDUSTRY HAS RELIED ON COMMUNICATIONS SYSTEMS DESIGNED AND STANDARDISED BY OTHER INDUSTRIES AND SEGMENTS. FOR THE ELECTRICAL INDUSTRY’S CONTINUED GROWTH AND DIGITAL TRANSFORMATION, IT IS NECESSARY TO UTILISE A PURPOSE-BUILT PROTOCOL FOR POWER TRANSMISSION AND DISTRIBUTION - IEC 61850. THIS ARTICLE SUMMARISES THE KEY CHARACTERISTICS OF IEC 61850 THAT SET IT APART FROM CURRENT STANDARD PRACTICE, AND WILL ALLOW THE INDUSTRY TO TAKE THE NEXT LEAP FORWARD TOWARDS A MORE CONNECTED AND DIGITAL FUTURE. IEC 61850 was released as a formal International Electrotechnical Commission (IEC) standard in 2009, with development stretching back into the mid-1990s. Initially conceived as a Substation Automation (SA) system to standardise control and communications for large substations and switchyards, it has expanded with products offering support down to the moulded case circuit breaker (MCCB) level of low voltage distribution.
Purpose-built for electrical systems To better understand the advantages of IEC 61850, it is easiest to compare it to the well-known and currently regularly used protocol Modbus. The table below lists the chief disadvantages
of Modbus when used in an electrical system and how IEC 61850 has been designed to address these limitations. IEC 61850’s characteristics address the practical needs of electrical transmission and distribution systems, rather than process control systems where most protocols have traditionally grown out of.
Achieving value with IEC 61850 By using IEC 61850, a great deal of value can be gained in creating solutions that are presently difficult or impossible to execute without additional engineering and intermediate equipment. This is on top of efficiencies gained from reducing overall complexity and integrating intelligent functions into necessary devices.
Modbus Time keeping / Synchronisation across network
NTP / SNTP implemented on Modbus TCP (> 1ms) None within Modbus RTU
For example: Selective zone interlocking through multiple levels of switchgear all the way up to medium voltage (MV). Implementation of various network protection functions, for example, directional overcurrent with only intelligent circuit breakers, as opposed to circuit breakers and protection relays. Transfer switching with only intelligent circuit breakers, as opposed to circuit breakers and automatic transfer switch (ATS) controllers and other auxiliary equipment. Sequence of events recording at up to 1µs resolution. As can be seen from the examples above, some of the efficiencies gained by removing complexity are achieved by selecting intelligent circuit breaker
IEC 61850
NTP / SNTP available PTP (IEEE 1588) (> 1µs)
Object – orientation
None, all data and devices exist as difficult to identify tables and lists. No way to enforce standardised tables and devices
All devices and data are object oriented. Common data for devices are standardised and generic, e.g. voltage, current, frequency, trip / close, etc
Hierarchy
Master / Slave protocol with all communication on a given bus initiated by the master
Distributed (peer to peer) model
Data contiguity
All data must be contiguous
Data prioritisation based on criticality of information, e.g., GOOSE messaging
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September 2021
