Remedial Action Scheme [RAS]

A scheme designed to detect predetermined System conditions and automatically take corrective actions that may include, but are not limited to, adjusting or tripping generation (MW and Mvar), tripping load, or reconfiguring a System(s). RAS accomplish objectives such as:
• Meet requirements identified in the NERC Reliability Standards;
• Maintain Bulk Electric System (BES) stability;
• Maintain acceptable BES voltages;
• Maintain acceptable BES power flows;
• Limit the impact of Cascading or extreme events.

The following do not individually constitute a RAS:
a. Protection Systems installed for the purpose of detecting Faults on BES Elements and isolating the faulted Elements
b. Schemes for automatic underfrequency load shedding (UFLS) and automatic undervoltage load shedding
(UVLS) comprised of only distributed relays
c. Out-of-step tripping and power swing blocking d. Automatic reclosing schemes
e. Schemes applied on an Element for non-Fault conditions, such as, but not limited to, generator loss-of- field, transformer top-oil temperature, overvoltage, or overload to protect the Element against damage by removing it from service
f. Controllers that switch or regulate one or more of the following: series or shunt reactive devices, flexible alternating current transmission system (FACTS) devices, phase-shifting transformers, variable-frequency transformers, or tap-changing transformers; and, that are located at and monitor quantities solely at the same station as the Element being switched or regulated
g. FACTS controllers that remotely switch static shunt reactive devices located at other stations to regulate the output of a single FACTS device
h. Schemes or controllers that remotely switch shunt reactors and shunt capacitors for voltage regulation that would otherwise be manually switched
i. Schemes that automatically de-energize a line for a non-Fault operation when one end of the line is open
j. Schemes that provide anti-islanding protection (g., protect load from effects of being isolated with generation that may not be capable of maintaining acceptable frequency and voltage)
k. Automatic sequences that proceed when manually initiated solely by a System Operator
l. Modulation of HVdc or FACTS via supplementary controls, such as angle damping or frequency damping applied to damp local or inter-area oscillations
m. Sub-synchronous resonance (SSR) protection schemes that directly detect sub-synchronous quantities (e.g., currents or torsional oscillations)
n. Generator controls such as, but not limited to, automatic generation control (AGC), generation excitation [e.g. automatic voltage regulation (AVR) and power system stabilizers (PSS)], fast valving, and speed governing