Voltage and reactive power control is one of those exam areas that looks simple until the question stem starts stacking conditions — a generator on AVR, a capacitor bank tripped, a voltage schedule from the Transmission Operator, and an RC watching an area-wide voltage decline. NERC standard VAR-001 (Voltage and Reactive Control) sits at the center of it, and RC exam writers love it because it forces you to keep the roles of the Reliability Coordinator (RC), Transmission Operator (TOP), and Generator Operator (GOP) straight while the grid is moving in real time.
This post gives you the test tips that consistently move the needle on VAR questions, then 5 practice items in NERC RC exam style with a full answer key.
Test Tips: VAR-001 on the NERC RC Exam
- Know who owns the voltage schedule. Under VAR-001, the Transmission Operator specifies the voltage schedule (or reactive power schedule) at the generator terminals or the point of interconnection. The Generator Operator is expected to maintain it. The RC does not normally set the local voltage schedule — the RC's role is wide-area coordination. Answer choices that put the RC in charge of setting individual plant voltage schedules are usually distractors.
- Automatic Voltage Regulators (AVRs) are the default. VAR-001 requires generators to operate with AVRs in service and in automatic voltage control mode whenever the unit is on line, unless the TOP has approved an exemption or a specific mode change. On the exam, if an AVR is taken out of service without TOP notification, that is a compliance problem — flag it.
- Notification timelines matter. When a generator cannot meet its voltage or reactive schedule (for example, an AVR failure, a status change, or a limit reached), the GOP must notify the TOP. Look for question stems that test whether the operator notified promptly — "as soon as practical" is the language you'll see.
- Reactive resources are more than just capacitors. Reactive support comes from generator excitation, synchronous condensers, static VAR compensators (SVCs), STATCOMs, shunt capacitors, and shunt reactors. Under-voltage problems typically call for injecting VARs (cap banks in, reactors out, boost excitation); over-voltage problems call for absorbing VARs (reactors in, caps out, reduce excitation). Get this direction right and half the trick questions solve themselves.
- Voltage is a local problem with a wide-area shadow. A single low-voltage bus can be a local issue, but sustained area-wide voltage decline is a leading indicator of voltage instability and possible voltage collapse. The RC's job is to see the pattern across TOP areas and coordinate mitigation — this is where VAR-001 intersects with IRO standards on wide-area view and real-time monitoring.
- Don't confuse VAR-001 with TOP standards. VAR-001 is about voltage/reactive control requirements on GOPs and TOPs. TOP-001 addresses SOL/IROL responsibilities. Exam questions often mix them — read carefully for whether the stem is really about a voltage schedule (VAR) or an operating limit (TOP/IRO).
5 Practice Questions
- Under NERC Standard VAR-001, who is responsible for specifying the voltage schedule (or reactive power schedule) at the generator terminals or point of interconnection?
- A. The Reliability Coordinator
- B. The Transmission Operator
- C. The Generator Operator
- D. The Balancing Authority
- A Generator Operator's automatic voltage regulator (AVR) trips off-line while the unit remains connected to the grid. Per VAR-001 expectations, the GOP should:
- A. Take no action until the next shift change
- B. Immediately trip the generator off-line
- C. Notify the Transmission Operator as soon as practical and coordinate on continued operation
- D. Notify only the Reliability Coordinator
- Voltages in a Transmission Operator's area are trending high across multiple 345 kV buses during a light-load overnight period. Which reactive action is most appropriate to help lower voltages?
- A. Switch shunt capacitor banks into service
- B. Switch shunt reactors into service and consider reducing generator excitation within limits
- C. Increase generator MW output across the area
- D. Request the RC to declare an EEA 2
- As a Reliability Coordinator, you observe sustained voltage decline across two adjoining Transmission Operator areas following a large generator trip. Consistent with the RC's role, your FIRST priority should be to:
- A. Direct each individual Generator Operator to change its voltage schedule
- B. Assess the wide-area condition and coordinate mitigating actions with the affected TOPs
- C. Wait for a TOP to declare an emergency before acting
- D. Immediately initiate manual load shedding across the footprint
- Under VAR-001, when is a generator expected to operate with its AVR in service and in automatic voltage control mode?
- A. Only during peak load hours
- B. Only when the RC issues a directive
- C. Whenever the unit is on-line, unless the Transmission Operator has approved an alternative
- D. Only during declared emergencies
Answer Key & Explanations
- B — The Transmission Operator. VAR-001 assigns the TOP responsibility for specifying voltage or reactive power schedules for generators in its area. The GOP is responsible for maintaining that schedule; the RC coordinates at the wide-area level rather than setting individual plant schedules.
- C — Notify the TOP as soon as practical and coordinate on continued operation. Under VAR-001, when a generator can no longer maintain its voltage or reactive schedule (including AVR status changes), the GOP is expected to notify the TOP promptly. The TOP then decides on operational adjustments; unilateral tripping or waiting until shift change is not consistent with the standard.
- B — Switch shunt reactors into service and consider reducing generator excitation within limits. High voltages under light load call for absorbing VARs. Reactors in and excitation trimmed (within reactive capability limits) reduce voltage. Adding capacitors would raise voltage further, and increasing MW output does not directly address the reactive problem.
- B — Assess the wide-area condition and coordinate mitigating actions with the affected TOPs. The RC's role is wide-area reliability. Voltage instability across adjoining areas requires the RC to build the picture and coordinate with TOPs on switching, generation redispatch, or, if warranted, more aggressive actions — before jumping to unilateral load shedding.
- C — Whenever the unit is on-line, unless the TOP has approved an alternative. VAR-001 requires generators to operate with AVRs in service and in automatic voltage control mode whenever on-line, with exceptions only as coordinated with the Transmission Operator.
Keep Going
VAR-001 is a high-yield exam topic because it forces you to keep RC, TOP, and GOP roles straight while the grid is actually moving. For more RC exam-prep drills, question sets, and guided study materials built by control-room veterans, visit EPG Solutions.