Power System Stability, Voltage Control, and Reactive Power Compensation (GATE/AE PYQ level)

 Q1. Power system stability deals with the ability of the system to:

A) Maintain synchronism under disturbances
B) Maintain voltage constant
C) Supply reactive power
D) None
Ans: A

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Q2. The swing equation is:
A) $M \frac{d^2δ}{dt^2} = P_m - P_e$
B) $M \frac{dδ}{dt} = P_m - P_e$
C) $J \frac{d^2ω}{dt^2} = T$
D) None
Ans: A

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Q3. The term $M$ in the swing equation represents:
A) Inertia constant
B) Damping factor
C) Synchronizing power
D) None
Ans: A

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Q4. The steady-state stability limit of a transmission line is given by:
A) $P_{max} = \frac{V_s V_r}{X} \sin δ_{max}$
B) $P = V_s V_r / R$
C) $P = V^2 / X$
D) None
Ans: A

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Q5. The maximum power transfer occurs when δ =
A) 90°
B) 60°
C) 45°
D) 30°
Ans: A

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Q6. Transient stability deals with:
A) Large disturbances
B) Small disturbances
C) Steady operation
D) None
Ans: A

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Q7. The equal area criterion is used to study:
A) Transient stability
B) Steady-state stability
C) Voltage stability
D) None
Ans: A

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Q8. The equal area criterion neglects:
A) Damping
B) Synchronizing torque
C) Mechanical losses
D) None
Ans: A

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Q9. Damping torque improves:
A) Transient stability
B) Steady-state stability
C) Both
D) None
Ans: C

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Q10. A system with low inertia will have:
A) Poor stability
B) High stability
C) Same stability
D) None
Ans: A

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Q11. Voltage stability refers to the ability of the system to:
A) Maintain acceptable voltages
B) Maintain frequency
C) Maintain synchronism
D) None
Ans: A

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Q12. Voltage collapse is caused by:
A) Excess reactive power demand
B) Active power shortage
C) Faults only
D) None
Ans: A

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Q13. Reactive power deficiency causes:
A) Voltage drop
B) Frequency drop
C) Power factor improvement
D) None
Ans: A

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Q14. Reactive power compensation improves:
A) Voltage profile
B) Power factor
C) Stability
D) All
Ans: D

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Q15. For stability improvement, shunt capacitors are installed:
A) Near load centers
B) At generating stations
C) At transformer secondary
D) None
Ans: A

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Q16. The main cause of transient instability is:
A) Sudden large disturbance
B) Small load variation
C) Temperature change
D) None
Ans: A

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Q17. In the power-angle curve, the x-axis represents:
A) Rotor angle (δ)
B) Speed
C) Frequency
D) Time
Ans: A

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Q18. Synchronizing power coefficient $P_s = \frac{dP_e}{dδ}$ determines:
A) Stability
B) Damping
C) Voltage
D) None
Ans: A

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Q19. If $P_s > 0$, the system is:
A) Stable
B) Unstable
C) Neutral
D) None
Ans: A

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Q20. The inertia constant $H$ is given in:
A) MJ/MVA
B) kJ/kVA
C) s²
D) None
Ans: A

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Q21. The mechanical input power during a fault is:
A) Constant
B) Zero
C) Variable
D) None
Ans: A

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Q22. The area under $P_m - P_e$ curve represents:
A) Kinetic energy change
B) Potential energy
C) Electrical energy
D) None
Ans: A

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Q23. The damping in power systems is primarily provided by:
A) Damper windings
B) Field resistance
C) Transformer leakage
D) None
Ans: A

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Q24. The unit of synchronizing power coefficient is:
A) MW/rad
B) MW
C) MVA
D) None
Ans: A

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Q25. The first swing stability is mainly concerned with:
A) Rotor angle deviation
B) Speed control
C) Voltage
D) None
Ans: A

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Q26. High-speed excitation improves:
A) Transient stability
B) Frequency stability
C) Load shedding
D) None
Ans: A

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Q27. The role of automatic voltage regulator (AVR) is to:
A) Maintain terminal voltage
B) Control reactive power
C) Improve stability
D) All
Ans: D

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Q28. Fast excitation helps to:
A) Counteract voltage dips
B) Decrease damping
C) Increase mechanical power
D) None
Ans: A

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Q29. A generator with higher H (inertia constant) will:
A) Resist speed changes
B) Oscillate faster
C) Be unstable
D) None
Ans: A

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Q30. Power system stabilizers (PSS) are used to:
A) Dampen oscillations
B) Increase power angle
C) Decrease excitation
D) None
Ans: A

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Q31. Reactive power is mainly required to:
A) Maintain voltage
B) Maintain frequency
C) Supply active load
D) None
Ans: A

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Q32. Shunt capacitors supply:
A) Leading VARs
B) Lagging VARs
C) Active power
D) None
Ans: A

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Q33. Shunt reactors absorb:
A) Leading VARs
B) Lagging VARs
C) Both
D) None
Ans: A

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Q34. Series capacitors are used to:
A) Compensate line reactance
B) Reduce resistance
C) Increase current
D) None
Ans: A

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Q35. Voltage stability margin is the difference between:
A) Operating voltage and collapse voltage
B) Sending and receiving voltage
C) No-load and full-load voltage
D) None
Ans: A

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Q36. Reactive power limit of a generator depends on:
A) Field current limit
B) Armature current limit
C) Both
D) None
Ans: C

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Q37. In an under-excited condition, a generator supplies:
A) Lagging current
B) Leading current
C) Unity current
D) None
Ans: B

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Q38. Overexcitation leads to:
A) Lagging power factor
B) Leading power factor
C) Both
D) None
Ans: A

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Q39. Voltage collapse generally starts from:
A) Weakest bus
B) Generator bus
C) Load bus
D) None
Ans: C

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Q40. A high X/R ratio in a system indicates:
A) Dominant reactive component
B) High resistance
C) Low reactance
D) None
Ans: A

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Q41. The primary control for frequency is:
A) Governor
B) Exciter
C) AVR
D) None
Ans: A

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Q42. Voltage control in generators is achieved by:
A) Field excitation
B) Turbine control
C) Mechanical governor
D) None
Ans: A

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Q43. The load angle δ increases with:
A) Active power
B) Reactive power
C) Both
D) None
Ans: A

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Q44. Reactive power flow between buses depends on:
A) Voltage magnitude difference
B) Phase angle difference
C) Both
D) None
Ans: A

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Q45. The best location for reactive compensation is:
A) Mid-point of the line
B) Sending end
C) Receiving end
D) None
Ans: A

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Q46. FACTS devices are used to:
A) Control reactive power dynamically
B) Stabilize voltage
C) Enhance transfer capacity
D) All
Ans: D

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Q47. SVC operates on the principle of:
A) Variable reactance
B) Fixed reactance
C) Current control
D) None
Ans: A

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Q48. STATCOM uses:
A) Voltage source converter
B) Current source converter
C) Induction motor
D) None
Ans: A

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Q49. UPFC controls:
A) Voltage, power flow, phase angle
B) Frequency only
C) Load only
D) None
Ans: A

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Q50. Power oscillation damping is achieved using:
A) Power System Stabilizer (PSS)
B) AVR
C) Governor
D) None
Ans: A

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Q51. Voltage control by tap-changing transformer is:
A) Slow
B) Fast
C) Instantaneous
D) None
Ans: A

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Q52. Reactive power compensation improves:
A) Voltage stability margin
B) Power factor
C) Both
D) None
Ans: C

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Q53. The critical clearing time is related to:
A) Transient stability
B) Voltage stability
C) Frequency control
D) None
Ans: A

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Q54. The smaller the clearing time, the:
A) More stable the system
B) Less stable
C) No effect
D) None
Ans: A

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Q55. The swing curve shows:
A) δ vs time
B) δ vs P
C) P vs t
D) None
Ans: A

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Q56. The per unit inertia constant (H) increases with:
A) Larger machine size
B) Smaller machine size
C) No relation
D) None
Ans: A

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Q57. The damping coefficient improves system:
A) Transient stability
B) Steady-state stability
C) Frequency response
D) None
Ans: A

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Q58. Voltage stability is more critical in:
A) Heavily loaded lines
B) Lightly loaded lines
C) No-load conditions
D) None
Ans: A

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Q59. Dynamic stability involves:
A) Small disturbances
B) Large disturbances
C) Both
D) None
Ans: A

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Q60. Power angle stability is associated with:
A) Rotor dynamics
B) Excitation control
C) Voltage regulation
D) None
Ans: A

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Q61. Increasing excitation improves:
A) Voltage
B) Reactive power output
C) Both
D) None
Ans: C

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Q62. The steady-state stability limit can be increased by:
A) Decreasing X
B) Increasing V
C) Both
D) None
Ans: C

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Q63. The transient stability margin depends on:
A) System inertia
B) Fault clearing time
C) Excitation
D) All
Ans: D

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Q64. A fast valving system acts on:
A) Steam turbine
B) Governor
C) Excitation
D) None
Ans: A

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Q65. The most effective control to improve transient stability is:
A) Fast excitation
B) Governor
C) PSS
D) None
Ans: A

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Q66. Load shedding helps maintain:
A) Frequency stability
B) Voltage
C) Power factor
D) None
Ans: A

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Q67. Frequency stability refers to:
A) Ability to maintain constant frequency
B) Maintain voltage
C) Maintain phase angle
D) None
Ans: A

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Q68. Under-voltage relays help prevent:
A) Voltage collapse
B) Overloading
C) Overvoltage
D) None
Ans: A

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Q69. Low power factor causes:
A) Higher current
B) Voltage drop
C) Both
D) None
Ans: C

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Q70. Reactive power demand increases during:
A) Motor starting
B) Line energization
C) Faults
D) All
Ans: D

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Q71. Overvoltage can occur due to:
A) Line dropping
B) Load rejection
C) Both
D) None
Ans: C

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Q72. The stability of a synchronous machine is improved by:
A) Increasing excitation
B) Increasing damping
C) Both
D) None
Ans: C

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Q73. Reactive power flow direction:
A) From higher to lower voltage
B) From lower to higher voltage
C) Depends on phase
D) None
Ans: A

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Q74. The system frequency decreases when:
A) Load > Generation
B) Load < Generation
C) Balanced
D) None
Ans: A

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Q75. Load-frequency control maintains:
A) Balance between generation and load
B) Constant voltage
C) Constant current
D) None
Ans: A

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Q76. Excitation control maintains:
A) Voltage
B) Reactive power
C) Both
D) None
Ans: C

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Q77. Fast voltage regulation prevents:
A) Voltage collapse
B) Frequency oscillation
C) Line overloading
D) None
Ans: A

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Q78. The equal area criterion assumes:
A) Constant mechanical input
B) No damping
C) Both
D) None
Ans: C

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Q79. Voltage instability leads to:
A) Gradual voltage fall
B) Oscillation
C) Frequency rise
D) None
Ans: A

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Q80. Reactive compensation using FACTS increases:
A) Voltage stability limit
B) Power transfer
C) Both
D) None
Ans: C

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Q81. The dynamic response of STATCOM is:
A) Very fast
B) Slow
C) Moderate
D) None
Ans: A

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Q82. Static VAR compensator controls:
A) Bus voltage
B) Line current
C) Frequency
D) None
Ans: A

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Q83. The generator capability curve is limited by:
A) Field heating
B) Armature heating
C) Stability
D) All
Ans: D

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Q84. The power triangle represents relation between:
A) P, Q, and S
B) V, I, and θ
C) Both
D) None
Ans: A

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Q85. Reactive power is measured in:
A) VAR
B) W
C) VA
D) None
Ans: A

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Q86. Poor voltage regulation indicates:
A) Large voltage drop
B) Stable voltage
C) Good compensation
D) None
Ans: A

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Q87. Voltage instability often occurs during:
A) Heavy load
B) Light load
C) Switching
D) None
Ans: A

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Q88. Generator excitation failure causes:
A) Voltage drop
B) Rotor oscillation
C) Instability
D) All
Ans: D

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Q89. The most common method of voltage control in transmission is:
A) Shunt compensation
B) Series compensation
C) Tap changer
D) None
Ans: A

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Q90. Reactive power compensation increases:
A) Power transfer capability
B) Efficiency
C) Voltage
D) All
Ans: D

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Q91. The transient energy function method is used to assess:
A) Stability
B) Voltage
C) Frequency
D) None
Ans: A

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Q92. The damping ratio ζ affects:
A) Oscillation decay rate
B) Voltage regulation
C) Power factor
D) None
Ans: A

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Q93. In a two-machine system, oscillations are termed as:
A) Inter-area oscillations
B) Local mode
C) Both
D) None
Ans: C

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Q94. FACTS controllers mainly control:
A) Impedance and voltage
B) Resistance
C) Power angle
D) None
Ans: A

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Q95. The first swing in transient stability occurs within:
A) 1–2 seconds
B) 5–10 seconds
C) 10–20 seconds
D) None
Ans: A

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Q96. The speed-governing system helps maintain:
A) Frequency
B) Voltage
C) Both
D) None
Ans: A

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Q97. Reactive power cannot:
A) Do real work
B) Be stored
C) Both
D) None
Ans: A

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Q98. The reactive power compensation device used for rapid control is:
A) STATCOM
B) SVC
C) TCSC
D) None
Ans: A

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Q99. The voltage stability improvement requires:
A) Reactive power support
B) Frequency control
C) Speed control
D) None
Ans: A

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Q100. The main objective of voltage and reactive power control is:
A) Maintain system voltage within limits
B) Minimize losses
C) Improve stability
D) All
Ans: D