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Power Systems Engineering Flashcards

7 cards from real BEE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. A transmission line has a sending-end voltage of 230 kV and a receiving-end voltage of 220 kV. What is the voltage regulation?

    Answer: 4.55%

    Voltage regulation = (V_NL − V_FL) / V_FL × 100 = (230 − 220) / 220 × 100 ≈ 4.55%.

  2. In power systems, what is the purpose of an auto-recloser on a distribution feeder?

    Answer: Automatically restore service after a temporary fault by re-energizing the line

    Auto-reclosers automatically open on a fault and reclose after a brief delay, restoring service if the fault was transient (e.g., lightning, tree branch).

  3. What is the significance of the 'critical clearing time' in transient stability analysis?

    Answer: The maximum fault duration for which the system remains transiently stable

    Critical clearing time is the maximum time a fault can persist before the generator loses synchronism; faults cleared faster than this keep the system stable.

  4. In a power transformer, what causes hysteresis and eddy current losses?

    Answer: Alternating magnetic flux in the core material

    Both hysteresis and eddy current losses are core (no-load) losses caused by the cyclic magnetization and induced circulating currents in the iron core.

  5. A 3-phase, 60 Hz synchronous generator has 4 poles. What is its synchronous speed?

    Answer: 1800 RPM

    Synchronous speed Ns = 120f/P = 120×60/4 = 1800 RPM.

  6. What is 'reactive power' in an AC power system and what unit is used to measure it?

    Answer: Power stored and returned by reactive elements, measured in volt-amperes reactive (VAR)

    Reactive power (Q) represents energy oscillating between source and reactive elements (inductors/capacitors) and is measured in VAR or MVAR.

  7. In the equal-area criterion for transient stability, what do the accelerating area and decelerating area represent?

    Answer: Energy gained by the rotor during fault and energy lost during post-fault swing

    The accelerating area is kinetic energy gained by the rotor during the fault; the decelerating area is kinetic energy absorbed post-fault; stability requires the decelerating area to be at least as large.