Case Study of Mission-Critical Smart Grid
Remedial Action Schemes Via Ethernet
Schweitzer Engineering Laboratories, Inc.
While special protection systems (SPSs) often shed
load, recent sophisticated remedial action schemes (RASs) reduce
or terminate generation output during an emergency condition.
Under certain load conditions, generation newly added to
previously balanced transmission grids creates system conditions
that violate accepted reliability criteria.
At Southern California Edison (SCE), RAS systems are
implemented to ensure reliable power system performance
following outages on a transmission grid network. They include
fast, automatic control actions to mitigate thermal overloads and
system instability upon the loss of one or more transmission lines.
With these automatic protection features, RAS systems are used
in place of expensive alternative measures, which include
reconductoring transmission lines, building new lines, and/or
adding new transformers. Testing at SCE demonstrates the
successful use of IEC 61850 GOOSE (Generic Object-Oriented
Substation Event) messages over a distance up to 460 miles to
collect analysis and arming data and transfer status and control
indications. Complete detection, alarming, calculation, and
remediation are completed in well under the 50-millisecond
Using standardized IEC 61850 GOOSE methods avoids the
customization required to implement individual local RAS
communications systems, allows centralized coordination of
arming, disarming, and system testing, and simplifies the
coordination of system maintenance. Reliability improves with
capabilities to monitor end-to-end grid parameters and quickly
respond to abnormal conditions.
These methods of mitigation are intended to be used
throughout the SCE area of operation as well as at all
interties to neighboring utilities to facilitate dynamic load
shedding/generation tripping and improved load management.
SPSs and RASs must be put in place to protect existing
systems that are called upon to serve new generation and load,
are intertied with weak systems, or have geographical
characteristics that reduce stability. Once protected, the
automatic load and generation control ensures stability while
improving production and reliability. Once these are in place,
wide-area monitoring and control are safely added to replace
state estimation with real-time state measurement and
Contemporary special protection systems (SPSs) and
remedial action scheme (RAS) systems are deployed via a
network of intelligent electronic devices (IEDs) that monitor
field conditions and react to contingency control actions.
Protection, control, and monitoring (PCM) IEDs that are
designed appropriately serve both PCM functions and monitor
and control functions for RAS systems. These PCM IEDs are
capable of serving both systems simultaneously; however,
separate IED networks are often deployed for physical
segregation. This simplifies design, installation, testing, and