The promise of substation integrated protection, control and
monitoring
John Tengdin, Editor-in-Chief
January 2001
From
the very first days of EPRI project RP3599 “Substation Integrated Protection
Control and Data Acquisition Requirements Specification”, the dream has always
been to reduce the maze of wiring that today interconnect relays with the power
system devices. Horror stories were told about rotting control cables, and the
need to replace them with a more up to date paradigm. The vastly increased
capability of microprocessor-based relays to gather and analyze data far beyond
the needs of their protective relaying functions has made these IEDs
(Intelligent Electronic Devices) the major source of substation data. Whether
it’s for operations, planning, or maintenance, the data from relays is needed
on a global basis.
With
the advent of a high-speed substation LAN, innovative ways of using these IEDs
and their data have been found (using the LAN) to improve protection and
operation. The Power System Relaying Committee (PSRC) Working Group H5 in a
report they are now completing has documented a large number of these possible
scenarios. A few of those scenarios have been used as examples in PSRC Working
Group H4 in draft IEEE Standard PC37.115 – “Standard Test Method for Use in
the Evaluation of Message Communications Between Intelligent Electronic Devices
in an Integrated Substation Protection, Control, and Data Acquisition System.”
The example scenarios are included in Informative Annexes to the draft standard.
These
scenarios utilize the substation LAN as a replacement for the large numbers of
interconnecting wires between relays, control switches, programmable logic
controllers, and RTUs (Remote Terminal Units) that are now typical in a
substation. But this is just the tip of the iceberg in possible savings in
substation wiring. Now a few forward looking utilities have taken the next major
step by installing the IEDs out in the substation yard – thus eliminating the
need to bring CT, VT, and control wiring back to the control house. One such
utility is the Bristol TN Electric System. In one of their distribution
substations, all of the IEDs are mounted out in the yard at the circuit
breakers, and are interconnected via the substation LAN. The control house is
small, as it only houses the station battery and the external communications
interface. Another is TVA, who has installed relaying IEDs out in the yard at
161 kV circuit breakers. These few examples are proving the real savings from a
distributed architecture substation automation system. We commend the engineers
responsible for these two, and look forward to learning about more.
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