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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. Which bus type in a power flow study has both voltage magnitude and angle specified as the slack (reference) bus?

    Answer: Vδ bus (swing bus)

    The slack (swing or Vδ) bus has fixed voltage magnitude and angle (usually 1.0∠0°) and absorbs the system's power imbalance.

  2. What is the main advantage of high-voltage DC (HVDC) transmission over AC transmission for very long distances?

    Answer: No reactive power losses and no skin effect over long distances

    HVDC has no reactive power losses, no charging current, no skin effect, and no stability limit over distance, making it efficient for bulk long-distance transmission.

  3. An underground cable has significantly higher capacitance per unit length than an overhead line. What operational problem does this create for long AC cables?

    Answer: Excessive charging current that can exceed the cable's thermal rating

    The high capacitance generates large charging currents that can occupy most of the cable's thermal capacity before any load current is even delivered.

  4. In a power system protection scheme, what is the purpose of a 'zone of protection'?

    Answer: To identify the section of the system that a specific relay is responsible for isolating during faults

    A protection zone defines the electrical boundary within which a relay detects faults and initiates breaker tripping to isolate only the faulted section.

  5. What is the purpose of a power system stabilizer (PSS) installed on a synchronous generator excitation system?

    Answer: Damp low-frequency electromechanical oscillations to improve small-signal stability

    A PSS adds a supplementary signal to the voltage regulator to provide damping torque, suppressing rotor oscillations (typically 0.1–2 Hz) that can destabilize interconnected systems.

  6. A distribution transformer is rated 25 kVA, 11 kV / 240 V. What is the full-load secondary current?

    Answer: 104.2 A

    I_secondary = kVA / V_secondary = 25,000 / 240 ≈ 104.2 A.

  7. What does the term 'spinning reserve' mean in power system operation?

    Answer: Generating capacity from units already online and synchronized, available to respond immediately to load increases

    Spinning reserve is synchronized online capacity running at part load that can instantly increase output to cover sudden generation loss or load pickup.