System Conditions

A Technical Committee of the Power & Energy Society.

Now bearing the title C37.2–IEEE Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations, this standard was perhaps the first substation configuration language when published by the American Institute of Electrical Engineers in 1928 as AIEE No. 26. It provided a means to describe, on an elementary diagram, the control and protection systems in automatic substations. Yes, even with just electromechanical relays, the control systems in these unattended substations could start and put on line rotary dc converters as the trolley or subway car loads grew (and take them off line in light load periods), detect dc overcurrent events and trip the affected 600 volt feeder. Then, based on the fault current’s rate of rise, block reclosing for downed trolley conductors but reclose for slower rates of rise (most likely a misoperation by a motorman).

The standard has been revised and updated many times since its original issue, and the 2008 revision was substantial. Of particular value to the users of IEC 61850 was the addition of a means to describe and document a communications network in a substation, even one with redundant communications elements. Added to IEEE C37.2 is a new device (Device number 16) defined as:

“data communications device - A device that supports the serial and / or network communications that are a part of the substation control and protection system.” Device number 16 is now used for data communications devices handling protective relaying or other substation communication traffic. The following suffix list identifies specific functions of a component identified as device 16. The first suffix letter must be either S (serial devices for RS-232, 422, or 485 communications) or E (for Ethernet components). The second and subsequent suffix letters may be one or more of the following letters to further define the device:

C - Security processing function [Virtual Private Network (VPN), encryption, etc.]

F - Firewall or message filter function

M - Network managed function [e.g., configured via Simple Network Management Protocol (SNMP)]

R - Router

S - Switch (Examples: Port switch on a dial up connection is 16SS, and an Ethernet switch is 16ES)

T - Telephone component (Example: auto-answer modem)

Annex B of the standard provides this additional information on the use of Device number 16 and its suffixes:

“In certain electric utility and industrial applications, data communications connections to protective relays are critical to the protection application. The data communications devices to which the relays connect are as important as auxiliary relays in protection system design and documentation.

For example, Ethernet local area networks (LANs) and wide area networks (WANs) are used for message transmission to carry out high-speed control and protection. A prime example for utilities is the use of IEC 61850 Part 8-1 GOOSE or GSSE messages in a substation Ethernet LAN environment to convey relaying element status, to provide interlocking, or to transmit a primary or backup trip command from one relay to another without conventional wiring. The Ethernet networks in substations are comprised of wired connections or fiber optic links, connecting protective relays and other IEDs in LANs based on managed Ethernet switches. The switch is, in fact, an elaborate message-processing computer with a list of settings that define how the protection messages are sent from one relay to another. Thus, Ethernet switches are the auxiliary relays for Ethernet-based protection and control systems. Furthermore, in some architectures, these substation LANs are connected to the utility enterprise WAN via Ethernet router(s) with broad functional capabilities and configuration settings. The configuration settings impact remote access to relays for monitoring, control, data collection, and wide-area protection, and are critical in the implementation of data communications security. See IEEE Std 1615™-2007 for more information. Similarly, serial data communications devices are important for communicating with relays for fault data retrieval, settings access, configuration, and for condition monitoring as part of a formal maintenance program.”

The C37.2 standard includes example diagrams showing the use of Device 16 for a serial network, for an Ethernet network, and for a dual redundant Ethernet network. It should be noted that the Substation Configuration Language in IEC 61850-6 deals only with logical nodes (not physical nodes) in describing the communications between elements. In addition, it does not include such devices as Ethernet routers, switches, firewalls, etc. All are included in Device 16, as shown in this example diagram for a dual redundant Ethernet based substation protection system. It shows how dual redundant relays might be integrated with an Ethernet LAN connected to the utility enterprise WAN. Each of the linked Ethernet connections shown for System A and System B in the diagram comprises a pair of noise-immune optical fibers for conveying Ethernet message packets in each direction. The

communications components in Figure B.3 with device 16 designations are:

• 16ESM – Ethernet managed switch. The Ethernet network port of each multifunction device 11 relay is connected to its own port on an Ethernet switch. The term “managed” refers to the fact that the switch operation itself can be monitored and controlled over the same network, and this is typically done from a remote location.
• 16ERFCM – Ethernet router, managed, with firewall and VPN for cyber-secured communications to the utility WAN. Fig

Note that the Substation Configuration Language in IEC 61850-6 deals only with logical nodes in a substation communication network, so redundant communication links are identical from a logical node perspective and so are out of scope – as are Ethernet routers, managed switches, firewalls and VPN.

There are a number of other additions to C37.2-2008. Since all of the available device numbers (other than Number 16) were in use, acronyms were added in this revision to describe seventeen functions new to C37.2. They are: AFD – Arc Flash Detector, CLK – Clock or timing source, DDR – Dynamic Disturbance Recorder, DFR – Digital Fault Recorder, ENV – Environmental data’ HIZ – High Impedance Fault Detector, HMI – Human Machine Interface, HST – Historian, LGC – Scheme logic (the function, as in a RAS– not a device like a PLC), MET – Substation Metering, PDC – Phasor Data Concentrator, PMU – Phasor Measurement Unit (the function), PQM – Power Quality Monitor, RIO - Remote Input/Output Device, RTU – Remote Terminal Unit / Data Concentrator, SER – Sequence of Events Recorder, TCM – Trip Circuit Monitor (the red light function remoted).

IEEE C37.2-2008 also includes a very comprehensive (three page) cross-reference table of IEEE function numbers and acronyms to IEC 61850 logical nodes. A new – much more user friendly – method (the “List Box” method) was added to describe the contents of a Device 11 – Multifunction Device, with its own example diagram. In addition, ten new suffix letter combinations were added to allow more complete descriptions of devices. Details of these additions may be found on the IEEE PES Substations Working Group C5 web site: grouper.ieee.org/groups/sub/wgc5/index.htm

With all these changes, control and protection engineers – and all those who use their elementary diagrams - will need easy access to a copy of IEEE C37.2-2008 Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations. You can’t learn all the details and use these additions to the language in C37.2 without it.