Special Protection Systems (SPS), now formally called Remedial Action Schemes (RAS), are one of the highest-leverage topics on the NERC Reliability Coordinator exam. They show up in questions on protection, coordination, and real-time operations — and the exam loves to test whether you understand the difference between a normal protection system and a RAS, plus who has approval authority. If you work them wrong in the control room, you can shed load you didn't need to shed or leave an IROL exposed. Here's how to lock this topic down.
Test Tips
- Know the definition cold. A Remedial Action Scheme is designed to detect predetermined System conditions and automatically take corrective actions — other than tripping only the faulted element — to maintain reliability. Actions typically include tripping generation, tripping load, reconfiguring the system, or runback of generation or HVDC. Standard-alone underfrequency (UFLS) and undervoltage (UVLS) load shedding, out-of-step tripping, and normal protective relaying are not RAS.
- PRC-012 is the umbrella standard. PRC-012 governs the RAS lifecycle: design review, database of RAS, evaluation, and periodic review by the Reliability Coordinator and Planning Coordinator. Expect questions about who reviews a new or modified RAS before it is placed in service — the answer path runs through the RC and PC, not just the owner.
- RC has the operational authority, not the design authority. The RC does not design the RAS, but the RC is the one who directs actions when a RAS misoperates, fails to operate, or must be taken out of service. Watch for exam distractors that put design approval on the RC alone.
- Failure-to-operate vs. misoperation. A RAS that fails to arm, fails to operate for its designed contingency, or operates for a condition it wasn't designed for is a RAS failure or misoperation and triggers reporting and evaluation. Don't confuse this with a PRC-004 protection system misoperation — RAS events have their own evaluation path under PRC-012.
- If a RAS is unavailable, the system is not. When a RAS is out of service, operating limits usually tighten because the RAS was relied on to keep the system inside an SOL or IROL post-contingency. The correct RC action is to adjust operating limits and coordinate with the TOP and GOP — not to ignore it because "nothing tripped."
- Memory aid — the four questions. On any RAS scenario question, ask: (1) Is it actually a RAS or just protection? (2) Who owns it and who reviews it? (3) What does it trip or run back? (4) If it's unavailable, what limit changes? Answering these four almost always narrows to one choice.
5 Practice Questions
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Which of the following is best classified as a Remedial Action Scheme (RAS)?
- A. A distance relay that trips a faulted 345 kV line for a phase-to-ground fault.
- B. A scheme that automatically trips 400 MW of generation upon loss of a specific 500 kV line to prevent thermal overload on a parallel path.
- C. A standard underfrequency load shedding program that sheds load at 59.5 Hz.
- D. A breaker failure scheme that trips adjacent breakers when a primary breaker fails to clear a fault.
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Under PRC-012, who is primarily responsible for the periodic review and evaluation of a Remedial Action Scheme to confirm it continues to meet its performance requirements?
- A. The Balancing Authority only.
- B. The Reliability Coordinator and Planning Coordinator, coordinating with the RAS-entity.
- C. The Generator Operator that owns the tripped generation.
- D. The Transmission Service Provider only.
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A RAS that normally arms for a specific N-1 contingency has been declared out of service for maintenance. What is the most appropriate immediate action for the Reliability Coordinator?
- A. Take no action; the RAS only operates for a contingency that may not occur.
- B. Direct that operating limits (SOL/IROL) be re-evaluated and tightened as needed to reflect the loss of the RAS, and coordinate with the affected TOPs and GOPs.
- C. Immediately shed 5% of load in the RAS footprint.
- D. Direct the RAS owner to restore the RAS within 30 minutes regardless of maintenance status.
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A RAS operates during real time but trips more generation than its design specified, resulting in a frequency excursion. This event is best characterized as:
- A. A protection system misoperation reportable only under PRC-004.
- B. A RAS misoperation that requires evaluation under PRC-012 and coordination with the RC.
- C. A normal RAS response; no evaluation is required as long as reliability was maintained.
- D. A Balancing Authority frequency control event only.
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Which statement about the Reliability Coordinator's authority over Remedial Action Schemes is most accurate?
- A. The RC designs and installs RAS at the request of the Transmission Owner.
- B. The RC has no involvement with RAS because RAS are automatic schemes.
- C. The RC reviews RAS for reliability impact, directs operating adjustments when a RAS is unavailable or misoperates, and coordinates with the PC and asset owners.
- D. The RC may unilaterally place any RAS in or out of service without notifying the owner.
Answer Key & Explanations
- B. A RAS detects predetermined system conditions and takes automatic corrective action beyond simply tripping the faulted element — such as tripping generation to protect a parallel path. Options A and D are normal protection; C is standard UFLS, which is specifically excluded from the RAS definition under PRC-012.
- B. PRC-012 assigns periodic evaluation and review of RAS to the Reliability Coordinator and Planning Coordinator, working with the RAS-entity that owns the scheme. A single functional entity (like the BA or TSP) does not carry that responsibility alone.
- B. When a RAS is unavailable, the post-contingency response it was providing is gone, so limits that relied on the RAS must be re-evaluated and typically tightened. The RC coordinates that adjustment with the TOP and GOPs; ignoring it (A) or shedding load preemptively (C) is incorrect.
- B. A RAS operating outside its designed action is a RAS misoperation and is evaluated under PRC-012, not treated as a routine event. PRC-004 covers standard protection system misoperations; a RAS has its own evaluation path, though both may apply in some events.
- C. The RC's role is oversight, coordination, and real-time operational authority — reviewing RAS for reliability impact, directing operating changes when a RAS is out of service or misoperates, and coordinating with the PC and asset owners. The RC does not design RAS (A), is not uninvolved (B), and does not act unilaterally without the owner (D).
Study Smarter, Pass Faster
RAS questions reward operators who can separate the definition from the operational response. Drill the four questions above on every RAS scenario, and PRC-012 stops being a trick topic. For the full RC exam prep library — study guides, drill sets, and control-room scenarios built by working operators — visit the EPG Solutions store and browse our NERC RC Exam Prep resources.