Power System Stability and Control MCQs

1. Which of the following phenomena can lead to power system instability?
A) Voltage collapse
B) Load shedding
C) Reactive power injection
D) All of the above
Answer: A

2. The swing equation in power system stability analysis describes the dynamics of:
A) Generator rotor angle
B) Bus voltage magnitude
C) Transmission line resistance
D) Load demand
Answer: A

3. The critical clearing angle in a power system is related to:
A) Frequency stability
B) Transient stability
C) Voltage stability
D) Steady-state stability
Answer: B

4. The main objective of power system stabilizers (PSS) is to:
A) Increase power flow capability
B) Mitigate small signal stability issues
C) Control generator excitation
D) Prevent voltage collapse
Answer: B

5. Damping torque in a synchronous generator helps in:
A) Increasing rotor speed
B) Reducing oscillations in rotor angle
C) Maintaining steady-state stability
D) Controlling active power flow
Answer: B

6. The transient stability of a power system is primarily affected by:
A) Small disturbances
B) Large disturbances
C) Load changes
D) Generator cooling
Answer: B

7. An under-excited synchronous generator:
A) Has leading power factor
B) Has lagging power factor
C) Is not synchronized to the grid
D) Requires more reactive power
Answer: B

8. The time interval between fault occurrence and the instant when the fault is cleared is crucial for:
A) Frequency control
B) Voltage regulation
C) Transient stability
D) Load shedding
Answer: C

9. In a power system stabilizer (PSS), the signal used for control is typically derived from:
A) Generator speed
B) Turbine temperature
C) Line current
D) Bus voltage
Answer: A

10. The angle δ in the swing equation represents the:
A) Difference between generator rotor angle and bus voltage angle
B) Phase difference between active and reactive power
C) Angular displacement of generator rotor
D) Voltage magnitude of the transmission line
Answer: C

11. The critical clearing time in transient stability analysis refers to the time:
A) After which the generator starts accelerating
B) Required to restore the transmission line
C) Available before the fault triggers instability
D) For load shedding to be effective
Answer: C

12. The term ‘voltage collapse’ in power systems refers to:
A) Sudden increase in system frequency
B) Loss of synchronism between generators
C) Sharp decline in bus voltages
D) Overloading of transmission lines
Answer: C

13. In a power system, FACTS devices are used primarily for:
A) Reactive power compensation
B) Active power control
C) Voltage regulation
D) Frequency stabilization
Answer: A

14. The main function of an automatic voltage regulator (AVR) is to:
A) Maintain constant bus voltage
B) Control generator excitation current
C) Synchronize generators
D) Stabilize system frequency
Answer: B

15. The primary purpose of load shedding in a power system is to:
A) Reduce generator speed
B) Improve power factor
C) Prevent system collapse
D) Increase transmission capacity
Answer: C

16. In power system stability analysis, the swing curve represents the variation of:
A) Active power with respect to time
B) Voltage magnitude with respect to frequency
C) Generator rotor angle with respect to time
D) Reactive power with respect to voltage
Answer: C

17. The concept of ‘voltage stability’ in a power system is concerned with:
A) Maintaining constant bus voltage
B) Preventing voltage collapse
C) Controlling power flow
D) Enhancing generator efficiency
Answer: B

18. The steady-state stability limit of a power system is primarily determined by:
A) Short circuit capacity
B) Power flow limits
C) Generator inertia
D) Line impedance
Answer: B

19. In a power system, the term ‘generator inertia’ refers to:
A) The resistance of the rotor to speed changes
B) The capability of the generator to supply reactive power
C) The ability of the generator to follow frequency changes
D) The kinetic energy stored in the rotating masses
Answer: D

20. An ‘excitation system’ in a synchronous generator is responsible for:
A) Supplying reactive power
B) Controlling active power output
C) Adjusting generator voltage
D) Increasing transmission efficiency
Answer: C

21. A ‘reactive power loop’ in power systems involves:
A) Control of active power flow
B) Exchange of reactive power between generators
C) Voltage regulation at buses
D) Monitoring frequency deviations
Answer: B

22. The primary function of a ‘load frequency control’ system in a power network is to:
A) Maintain constant generator speed
B) Balance active and reactive power
C) Regulate bus voltages
D) Stabilize system frequency
Answer: D

23. The term ‘damping ratio’ in power system stability analysis indicates:
A) Rate of change of generator speed
B) Rate of change of bus voltage
C) Rate of decay of oscillations
D) Rate of active power transfer
Answer: C

24. A ‘static VAR compensator’ (SVC) is used in power systems to:
A) Improve generator efficiency
B) Compensate for reactive power demand
C) Control generator frequency
D) Enhance transmission line capacity
Answer: B

25. A ‘voltage regulator’ in a power system primarily controls:
A) Generator speed
B) Generator torque
C) Generator excitation
D) Generator cooling
Answer: C

26. The term ‘power angle’ in power system stability analysis refers to:
A) Difference between generator rotor angle and bus voltage angle
B) Phase difference between active and reactive power
C) Angular displacement of generator rotor
D) Voltage magnitude of the transmission line
Answer: A

27. A ‘fault ride-through capability’ of a generator refers to its ability to:
A) Maintain constant active power output during faults
B) Synchronize with other generators
C) Withstand sudden frequency changes
D) Resume normal operation after faults
Answer: A

28. The ‘steady-state stability limit’ of a power system is primarily determined by:
A) Transient stability
B) Voltage regulation
C) Power flow limits
D) Generator inertia
Answer: C

29. In a power system, the term ‘angle stability’ refers to the ability of:
A) Generators to maintain constant power output
B) Voltage regulators to control bus voltages
C) Transmission lines to handle power flow
D) Synchronous generators to maintain phase synchronization
Answer: D

30. A ‘dynamic braking resistor’ in a generator is used to:
A) Improve generator efficiency
B) Absorb excess mechanical energy
C) Control reactive power flow
D) Stabilize system frequency
Answer: B

31. The ‘critical fault clearing time’ in transient stability analysis is the time required to:
A) Restore the transmission line
B) Clear a fault and prevent instability
C) Implement load shedding
D) Reduce generator inertia
Answer: B

32. The ‘inertia constant’ of a synchronous generator represents its:
A) Maximum power output capability
B) Mechanical strength
C) Ability to resist speed changes
D) Efficiency under load
Answer: C

33. ‘Primary frequency control’ in power systems is typically achieved through:
A) Generator droop characteristics
B) Load shedding schemes
C) Automatic voltage regulators
D) FACTS devices
Answer: A

34. The term ‘dynamic stability’ in a power system refers to the ability to:
A) Maintain constant voltage levels
B) Withstand large disturbances
C) Adjust reactive power flow
D) Control power factor
Answer: B

35. A ‘pole slipping’ event in power systems can lead to:
A) Voltage collapse
B) Frequency deviation
C) Phase imbalance
D) Load shedding
Answer: A

36. The ‘reactive power demand’ in a power system is primarily influenced by:
A) Active power flow
B) Generator speed
C) Transmission line voltage
D) Generator loading
Answer: C

37. The term ‘synchronizing power’ in power systems refers to:
A) Power required to synchronize generators
B) Power transferred between synchronous generators
C) Power exchanged during islanding events
D) Power factor control
Answer: A

38. The ‘voltage collapse’ phenomenon in power systems is often triggered by:
A) Excessive reactive power consumption
B) High active power demand
C) Generator overload
D) Fault clearance delay
Answer: A

39. The ‘angle stability limit’ in power systems is primarily determined by:
A) Active power transfer capability
B) Reactive power compensation
C) Generator synchronization
D) Rotor angle deviation
Answer: D

40. A ‘transient voltage dip’ in a power system can result from:
A) Sudden load changes
B) Generator speed fluctuations
C) Faults on transmission lines
D) Reactor switching
Answer: C

41. The ‘swing equation’ in power system stability analysis describes the dynamics of:
A) Generator active power
B) Bus voltage phase angle
C) Generator rotor angle
D) Transmission line resistance
Answer: C

42. A ‘load shedding’ scheme in a power system is activated to:
A) Increase generator output
B) Improve system stability
C) Control bus voltages
D) Compensate for reactive power
Answer: B

43. The ‘fault duration’ in transient stability analysis affects:
A) Reactive power flow
B) Active power transfer
C) Rotor angle stability
D) Generator efficiency
Answer: C

44. In power system stability analysis, ‘small signal stability’ refers to the stability of:
A) Steady-state conditions
B) Large disturbances
C) Small perturbations
D) Reactive power flows
Answer: C

45. A ‘power system stabilizer’ (PSS) is primarily designed to improve:
A) Reactive power compensation
B) Voltage regulation
C) Small signal stability
D) Rotor angle stability
Answer: D

46. The ‘critical clearing angle’ in transient stability analysis is defined as the angle between:
A) Generator rotor angle and bus voltage
B) Pre-fault and post-fault conditions
C) Generator speed and turbine torque
D) Fault clearance and stability restoration
Answer: B

47. The ‘inrush current’ in transformers during energization can lead to:
A) Voltage instability
B) Overcurrent protection operation
C) Generator synchronization issues
D) Fault on transmission lines
Answer: B

48. The ‘steady-state stability’ of a power system is determined primarily by:
A) Short circuit capacity
B) Generator inertia
C) Power flow limits
D) Voltage regulation
Answer: C

49. The ‘dynamic braking resistor’ in a generator helps in:
A) Stabilizing system frequency
B) Controlling reactive power flow
C) Preventing generator overheating
D) Absorbing excess mechanical energy
Answer: D

50. The ‘angular stability’ of a synchronous generator refers to its ability to:
A) Maintain constant power output
B) Resist sudden frequency changes
C) Control active power flow
D) Maintain phase synchronization
Answer: D

Power System Stability and Control MCQs

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