Underfrequency Load Shedding (UFLS) is the last automatic line of defense between a severe generation-load imbalance and full system collapse. On the NERC RC exam, PRC-006 questions test whether you understand who designs the program, who implements it, and how the Reliability Coordinator fits into a coordinated Interconnection-wide scheme. If you work in a control room, you already know UFLS relays trip in cycles — not minutes. The exam wants to see that you know the standard behind the relay.
Why This Topic Matters on the RC Exam
PRC-006 (Automatic Underfrequency Load Shedding) is one of the standards that ties together Planning Coordinators, Transmission Owners, Distribution Providers, and the Reliability Coordinator. Exam writers love it because a single scenario can test coordination, roles, and real-time judgment all at once. Miss the role assignments and you will lose easy points.
Test Tips
- Know who owns the program. The Planning Coordinator (PC) is responsible for developing and maintaining the UFLS program for its Planning Coordinator area under PRC-006. The RC does not design UFLS — the RC coordinates across PC areas within its footprint. If an answer choice says "the RC designs the UFLS program," it is wrong.
- Know who implements it. UFLS relays sit on the distribution and transmission system and are owned and maintained by the entities identified in the PC's program — typically Transmission Owners (TO) and Distribution Providers (DP). The exam will test whether you can separate design (PC) from implementation (TO/DP).
- Remember the purpose: UFLS is designed to arrest declining frequency and prevent cascading, uncontrolled separation, and blackout during a severe imbalance. It is not a normal-operations tool — it is automatic and event-driven.
- Watch for the RC coordination angle. When a UFLS program crosses PC boundaries within an Interconnection, coordination is required. Questions that mention "neighboring PC" or "across the Interconnection" are usually pointing to the coordination requirement.
- Do not confuse UFLS with manual load shedding. Manual firm load shedding under emergency operations (EOP-011) is a separate tool the BA/TOP/RC use during an EEA 3. UFLS is automatic and relay-based. If the stem says "the operator sheds load," it is not UFLS.
- Memory aid: PC designs, TO/DP implements, RC coordinates, relays act — operators do not push the UFLS button.
5 Practice Questions
-
Under NERC PRC-006, which functional entity is responsible for developing the Underfrequency Load Shedding (UFLS) program for its area?
A. Reliability Coordinator (RC)
B. Balancing Authority (BA)
C. Planning Coordinator (PC)
D. Transmission Operator (TOP) -
UFLS is primarily designed to:
A. Reduce area control error (ACE) during normal operations
B. Arrest declining system frequency to prevent uncontrolled separation, cascading, and blackout
C. Provide contingency reserve within 15 minutes of a generator trip
D. Manage transmission line loading during congestion events -
A severe frequency excursion trips a block of UFLS relays across two neighboring Planning Coordinator areas within the same Interconnection. Which coordination expectation best fits PRC-006?
A. Each PC operates independently; no coordination is required
B. The RC designs a single UFLS program that overrides both PCs
C. Neighboring PCs are expected to coordinate their UFLS programs so the overall Interconnection response is effective
D. The BA reprograms the UFLS relays in real time to match the disturbance -
During a real-time event, system frequency drops rapidly and UFLS relays begin operating. What is the RC's most appropriate immediate role?
A. Manually arm and trip UFLS relays from the control center
B. Monitor the wide-area response, coordinate with BAs and TOPs, and take the most conservative action to preserve reliability
C. Wait for the Planning Coordinator to authorize any response
D. Direct all Distribution Providers to restore shed load immediately to minimize customer impact -
Which of the following statements about UFLS is TRUE?
A. UFLS is a manual load-shedding tool operators use during an EEA 2
B. UFLS relays are owned and maintained by the RC
C. UFLS is an automatic, relay-based scheme that operates on frequency, independent of operator action
D. UFLS replaces the need for contingency reserves under BAL-002
Answer Key & Explanations
- C — Planning Coordinator (PC). Under PRC-006, the PC is responsible for developing and maintaining the UFLS program for its area. The RC coordinates across PCs; it does not design the program.
- B. UFLS exists to arrest a declining frequency excursion and prevent cascading and uncontrolled separation — that is the stated reliability purpose of PRC-006.
- C. PRC-006 expects UFLS programs to be coordinated across PC areas within an Interconnection so the overall automatic response is effective. Independent, uncoordinated programs are exactly what the standard is written to prevent.
- B. The RC is a wide-area coordinator. During a real-time frequency event, the RC monitors, coordinates with BAs and TOPs, and — consistent with IRO-001 — takes the most conservative action when reliability is uncertain. The RC does not manually arm UFLS relays.
- C. UFLS is automatic and relay-based. It is not a manual operator tool, is not owned by the RC, and does not replace contingency reserve obligations under BAL-002.
Take It Further
If you are prepping for the NERC RC exam, drill PRC-006 alongside EOP-011 (manual load shedding) and BAL-003 (frequency response) — the three together cover the full frequency-defense picture the exam loves to test. EPG Solutions builds RC exam prep resources by control-room operators, for control-room operators. Browse the EPG Solutions store to find current study guides and practice sets.