Power System Dynamics, Excitation Systems, Power System Stabilizers (PSS), FACTS & HVDC-based Stability Enhancement

 Q1. The swing equation of a synchronous machine represents:

A) Rotor dynamics
B) Electrical circuit
C) Governor control
D) Excitation system
Ans: A

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Q2. In the swing equation, accelerating power $P_a = P_m - P_e$:
A) Determines change in rotor angle
B) Determines excitation
C) Determines damping
D) None
Ans: A

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Q3. The damping coefficient is added in swing equation to:
A) Reduce oscillations
B) Increase synchronizing torque
C) Improve transient limit
D) None
Ans: A

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Q4. The rotor angle δ increases when:
A) $P_m > P_e$
B) $P_m < P_e$
C) $P_m = P_e$
D) None
Ans: A

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Q5. In small-signal stability studies, linearization is done around:
A) Steady-state operating point
B) Fault point
C) Peak load
D) None
Ans: A

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Q6. The synchronizing power coefficient $P_s = \frac{dP_e}{d\delta}$ determines:
A) Stiffness of synchronism
B) Damping
C) Frequency deviation
D) None
Ans: A

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Q7. A higher synchronizing power coefficient means:
A) Stronger synchronism
B) Weaker system
C) More oscillations
D) None
Ans: A

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Q8. The natural frequency of rotor oscillations (Hz) ≈
A) $\frac{1}{2\pi}\sqrt{\frac{P_s}{M}}$
B) $\sqrt{M/P_s}$
C) $\frac{P_s}{M}$
D) None
Ans: A

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Q9. The inertia constant (H) affects:
A) Rate of change of speed
B) Voltage
C) Frequency only
D) None
Ans: A

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Q10. Damping torque is produced by:
A) Speed-sensitive elements
B) Excitation voltage
C) Load torque
D) None
Ans: A

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Q11. Fast acting exciters:
A) Improve transient stability
B) Reduce steady-state stability
C) Worsen damping
D) None
Ans: A

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Q12. The AVR controls:
A) Terminal voltage
B) Frequency
C) Load current
D) None
Ans: A

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Q13. Increasing AVR gain improves:
A) Voltage control
B) Damping
C) Both
D) None
Ans: A

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Q14. Excessive AVR gain may cause:
A) Voltage oscillations
B) Frequency instability
C) Speed fluctuations
D) None
Ans: A

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Q15. The Power System Stabilizer (PSS) provides:
A) Damping torque proportional to speed deviation
B) Synchronizing torque
C) Voltage boost
D) None
Ans: A

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Q16. The input to a PSS is usually:
A) Rotor speed deviation (Δω)
B) Voltage
C) Load angle
D) None
Ans: A

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Q17. The purpose of washout circuit in PSS is to:
A) Block DC signals
B) Amplify low frequency
C) Reduce gain
D) None
Ans: A

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Q18. A phase compensation circuit in PSS provides:
A) Phase lead to compensate excitation lag
B) Phase lag
C) Gain reduction
D) None
Ans: A

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Q19. The output of PSS adds to:
A) Excitation system input
B) Governor input
C) AVR output
D) None
Ans: A

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Q20. The damping torque provided by PSS is:
A) Proportional to Δω
B) Inversely proportional to δ
C) Constant
D) None
Ans: A

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Q21. The IEEE Type-1 excitation system uses:
A) DC exciter with amplifier
B) AC exciter
C) Static converter
D) None
Ans: A

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Q22. Static excitation systems have:
A) Fastest response
B) Slow response
C) Mechanical delays
D) None
Ans: A

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Q23. Excitation control indirectly affects:
A) Reactive power and voltage
B) Real power
C) Frequency
D) None
Ans: A

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Q24. The feedback in AVR loop improves:
A) System stability
B) Gain
C) Phase lag
D) None
Ans: A

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Q25. Power system oscillations are typically in range of:
A) 0.2–2 Hz
B) 10–20 Hz
C) 50–60 Hz
D) 100–200 Hz
Ans: A

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Q26. Multi-machine stability involves:
A) Relative rotor angle oscillations
B) Frequency variation
C) Excitation voltage
D) None
Ans: A

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Q27. FACTS devices like SSSC & STATCOM help in:
A) Damping power oscillations
B) Increasing voltage
C) Reducing frequency
D) None
Ans: A

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Q28. The effective inertia of an interconnected system:
A) Increases with number of generators
B) Decreases
C) Remains constant
D) None
Ans: A

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Q29. The critical clearing time (CCT) is defined as:
A) Max fault duration for stability
B) Minimum time for clearing
C) Equal area duration
D) None
Ans: A

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Q30. HVDC links improve stability by:
A) Fast controllable power flow
B) Reactive power injection
C) Phase shift
D) None
Ans: A

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Q31. The converter in HVDC system controls:
A) Real and reactive power
B) Voltage only
C) Frequency only
D) None
Ans: A

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Q32. In a monopolar HVDC system, the return path is via:
A) Ground or metallic return
B) Second conductor
C) Neutral
D) None
Ans: A

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Q33. The reactive power demand of a line-commutated HVDC converter is approximately:
A) 50–60% of DC power
B) 10%
C) 80%
D) None
Ans: A

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Q34. Voltage source converters (VSC) in HVDC systems can:
A) Independently control active and reactive power
B) Control only active power
C) Control frequency
D) None
Ans: A

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Q35. The main advantage of VSC-HVDC over LCC-HVDC is:
A) Black start capability
B) No commutation failure
C) Compact filters
D) All
Ans: D

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Q36. A VSC-HVDC uses:
A) IGBT-based converters
B) Thyristors
C) Diodes
D) None
Ans: A

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Q37. The converter reactive power can be compensated by:
A) STATCOM
B) SVC
C) Both
D) None
Ans: C

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Q38. The power reversal in LCC-HVDC is done by:
A) Reversing polarity of DC voltage
B) Reversing current
C) Changing control angle
D) None
Ans: A

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Q39. The DC voltage in HVDC link is controlled by:
A) Rectifier station
B) Inverter station
C) Both
D) None
Ans: A

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Q40. The reactive power of converter increases with:
A) Firing angle
B) Voltage
C) DC current
D) None
Ans: A

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Q41. The stability improvement using HVDC is due to:
A) Fast controllable real power flow
B) Reduced reactive current
C) Voltage boost
D) None
Ans: A

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Q42. The PSS mainly improves:
A) Damping of low frequency oscillations
B) Transient stability
C) Voltage control
D) None
Ans: A

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Q43. The exciter time constant affects:
A) Dynamic response
B) Inertia
C) Synchronizing torque
D) None
Ans: A

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Q44. The main objective of excitation system design is to:
A) Provide fast voltage control with adequate damping
B) Maintain constant speed
C) Control current
D) None
Ans: A

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Q45. FACTS controllers for stability enhancement include:
A) SSSC, STATCOM, UPFC
B) OLTC, AVR
C) PSS, Governor
D) None
Ans: A

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Q46. A TCSC (Thyristor Controlled Series Capacitor) adjusts:
A) Line reactance
B) Shunt susceptance
C) Frequency
D) None
Ans: A

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Q47. A UPFC (Unified Power Flow Controller) can simultaneously:
A) Control voltage, impedance & phase angle
B) Control current only
C) Control frequency
D) None
Ans: A

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Q48. The UPFC combines functions of:
A) STATCOM + SSSC
B) TCSC + OLTC
C) SVC + TCR
D) None
Ans: A

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Q49. Dynamic reactive power compensation devices include:
A) SVC, STATCOM
B) Capacitor banks
C) OLTC
D) None
Ans: A

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Q50. The role of FACTS in stability is to:
A) Increase damping torque
B) Increase synchronizing torque
C) Both
D) None
Ans: C