Practice Test Geeks(EGSA) Electrical Generating Systems Association Certified Practice Test
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Voltage Regulation and Excitation Flashcards

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  1. The per-unit voltage regulation formula is (V_NL - V_FL) / V_FL. If no-load voltage is 480V and full-load voltage is 460V, what is the voltage regulation?

    Answer: 4.35%

    VR = (480 - 460) / 460 = 20/460 = 0.0435 = 4.35%.

  2. What is the function of a power factor controller (PFC) used with some AVRs?

    Answer: To maintain the generator at a fixed power factor setpoint

    A PFC mode AVR regulates excitation to hold a target power factor rather than a target voltage, commonly used when a generator operates in parallel with an infinite bus (utility).

  3. What does the term 'synchronous reactance' (Xs) represent in a generator?

    Answer: The AC reactance that limits armature current under steady-state fault conditions

    Synchronous reactance is the effective AC impedance of the stator that governs steady-state current flow and is a key parameter in calculating voltage regulation.

  4. A generator's AVR is set to maintain 480V at the generator terminals. A remote sensing option instead measures voltage at:

    Answer: A point further in the distribution system, such as main bus or load center

    Remote sensing allows the AVR to regulate voltage at a point downstream from the generator terminals, compensating for feeder voltage drops under load.

  5. Which condition can cause an AVR to ceiling excitation (drive field current to maximum)?

    Answer: A three-phase fault near the generator terminals causing voltage collapse

    During a terminal fault, generator voltage collapses to near zero, causing the AVR to detect a large error and drive excitation to its ceiling to try to restore voltage.

  6. What is the primary purpose of an underexcitation limiter (UEL) in a generator excitation system?

    Answer: To prevent the generator from absorbing excessive reactive power and losing synchronism

    The UEL prevents the excitation from dropping so low that the generator absorbs reactive power beyond its capability curve limits, which could lead to loss of synchronism.

  7. In a compound excitation system, what provides the excitation source at zero speed (before the machine is self-exciting)?

    Answer: A separate battery or PMG-based starting supply

    Compound excitation relies on current transformers from the generator output, so a separate startup supply (battery, PMG, or auxiliary source) is needed at zero output.