Power System Protection and Relaying MCQs

1. Which of the following is the primary objective of power system protection?
A) Prevent system overload
B) Minimize system losses
C) Ensure continuity of supply
D) Improve power quality
Answer: C

2. The time-current characteristic of a protective relay is also known as:
A) R-X diagram
B) Z-B diagram
C) T-Q diagram
D) I-T diagram
Answer: D

3. In an overcurrent relay, the time of operation ________ with increasing fault current.
A) Decreases
B) Increases
C) Remains constant
D) Becomes unpredictable
Answer: A

4. Distance protection relays primarily operate based on:
A) Voltage magnitude
B) Current magnitude
C) Impedance measurement
D) Power factor
Answer: C

5. The term “reach” in distance protection relays refers to:
A) Maximum fault current the relay can handle
B) Maximum distance up to which the relay can detect faults
C) Maximum power dissipation capability
D) Maximum sensitivity of the relay
Answer: B

6. Which type of relay is used for the protection of transmission lines against faults?
A) Differential relay
B) Overcurrent relay
C) Distance relay
D) Directional relay
Answer: C

7. In directional overcurrent relays, operation occurs when:
A) Current exceeds a set value in any direction
B) Current exceeds a set value and flows in the predetermined direction
C) Voltage exceeds a set value in the intended direction
D) Both current and voltage exceed preset values
Answer: B

8. Buchholz relay is used for the protection of:
A) Transformers
B) Generators
C) Transmission lines
D) Motors
Answer: A

9. In a generator protection scheme, loss of excitation protection is used to:
A) Protect against short circuits
B) Prevent overheating
C) Prevent voltage collapse
D) Protect against over-speed
Answer: C

10. The primary function of a synchrocheck relay is to:
A) Synchronize generators
B) Check synchronization of generators
C) Monitor synchronizing torque
D) Protect against mechanical failures
Answer: B

11. A negative sequence relay is used to protect against:
A) Phase-to-phase faults
B) Ground faults
C) Unbalanced loads
D) Overvoltage conditions
Answer: C

12. In transformer differential protection, which principle is typically used?
A) Voltage balance
B) Current balance
C) Impedance balance
D) Power balance
Answer: B

13. A backup protection relay is used to:
A) Provide primary protection
B) Provide additional protection in case primary protection fails
C) Protect against transient faults
D) Protect against insulation breakdown
Answer: B

14. Which relay detects faults in the rotor circuit of a synchronous machine?
A) Stator earth fault relay
B) Stator inter-turn relay
C) Rotor earth fault relay
D) Differential relay
Answer: C

15. The term “zone of protection” refers to:
A) Area protected by a relay
B) Operating time of a relay
C) Voltage level of a relay
D) Power factor of a relay
Answer: A

16. In a busbar protection scheme, which type of relay is commonly used?
A) Differential relay
B) Overcurrent relay
C) Distance relay
D) Directional relay
Answer: A

17. A static relay differs from an electromagnetic relay in that it:
A) Uses semiconductor devices for its operation
B) Operates without any power supply
C) Requires more maintenance
D) Is more sensitive to faults
Answer: A

18. An underfrequency relay is used to protect against:
A) Overvoltage conditions
B) Overfrequency conditions
C) Underfrequency conditions
D) Ground faults
Answer: C

19. A surge diverter is used in power systems to protect against:
A) Overcurrent conditions
B) Overvoltage conditions
C) Underfrequency conditions
D) Insulation failures
Answer: B

20. The purpose of a supervisory control and data acquisition (SCADA) system in protection is to:
A) Initiate protective actions remotely
B) Monitor voltage fluctuations
C) Maintain system frequency
D) Regulate power factor
Answer: A

21. In which type of protection scheme does the relay operate based on the sequence of events and the time at which they occur?
A) Sequence of events recorder
B) Time-graded protection
C) Numerical protection
D) Sequential protection
Answer: D

22. A sensitive earth fault relay is used to protect against:
A) High-voltage conditions
B) Ground faults in solidly grounded systems
C) Overcurrent conditions
D) Insulation failures
Answer: B

23. In transformer protection, which relay detects faults between turns of the same winding?
A) Differential relay
B) Overcurrent relay
C) Buchholz relay
D) Restricted earth fault relay
Answer: D

24. The primary function of a differential relay is to protect against:
A) Overloads
B) Short circuits
C) Voltage surges
D) Insulation failures
Answer: B

25. A load shedding scheme is used to:
A) Shed excess load during peak demand
B) Protect against short circuits
C) Improve power factor
D) Regulate system frequency
Answer: A

26. In which protection scheme does the relay operate based on the ratio of the voltage to the current?
A) Impedance protection
B) Differential protection
C) Reactance protection
D) Phase comparison protection
Answer: A

27. An auto-reclosing scheme is used primarily to:
A) Prevent overload
B) Clear transient faults
C) Protect against insulation failures
D) Regulate system voltage
Answer: B

28. Which of the following is not a type of distance relay?
A) Mho relay
B) Reactance relay
C) Quadrilateral relay
D) Permissive overreaching transfer trip (POTT)
Answer: D

29. Which protection scheme is used to protect motors against overcurrents and ground faults?
A) Differential protection
B) Directional protection
C) Overcurrent protection
D) Buchholz protection
Answer: C

30. A relay which operates when the power factor of the system falls below a preset value is called:
A) Power factor relay
B) Directional relay
C) Synchronizing relay
D) Differential relay
Answer: A

31. The ANSI device number 50 refers to:
A) Instantaneous overcurrent relay
B) Time overcurrent relay
C) Directional overcurrent relay
D) Stator earth fault relay
Answer: B

32. A fault locator relay is used to:
A) Locate the exact position of a fault in a transmission line
B) Record events leading to a fault
C) Monitor voltage fluctuations
D) Prevent insulation breakdown
Answer: A

33. Which protection scheme is used to protect a generator against loss of field?
A) Differential protection
B) Loss of excitation protection
C) Overcurrent protection
D) Buchholz protection
Answer: B

34. A relay that operates when the voltage in one phase of a three-phase system exceeds the voltage in the other phases is called:
A) Voltage balance relay
B) Differential relay
C) Phase balance relay
D) Unbalance voltage relay
Answer: D

35. An arc protection relay is used to detect:
A) Overcurrent conditions
B) Overvoltage conditions
C) Arcing faults
D) Insulation failures
Answer: C

36. In a generator protection scheme, a reverse power relay operates when:
A) Generator power output is below a certain level
B) Generator power output is above a certain level
C) Generator runs in reverse direction
D) Generator voltage exceeds a certain value
Answer: A

37. The purpose of a surge arrester in a power system is to protect against:
A) Overcurrent conditions
B) Overvoltage conditions
C) Underfrequency conditions
D) Insulation failures
Answer: B

38. A differential protection relay will not operate for:
A) Phase-to-phase fault
B) Phase-to-ground fault
C) Differential fault
D) Busbar fault
Answer: D

39. A relay that operates when the impedance measured from the relay location to the fault point falls below a certain value is known as:
A) Distance relay
B) Reactance relay
C) Mho relay
D) Quadrilateral relay
Answer: A

40. A relay that operates when the current in a circuit exceeds a predetermined value is called:
A) Differential relay
B) Overcurrent relay
C) Directional relay
D) Restricted earth fault relay
Answer: B

41. The IEEE device number 87 refers to:
A) Distance relay
B) Busbar protection relay
C) Transformer differential relay
D) Differential generator relay
Answer: C

42. Which protection scheme is used for the protection of a transmission line against overvoltages caused by lightning?
A) Lightning arrester
B) Surge diverter
C) Distance relay
D) Ground fault protection
Answer: B

43. An under-voltage relay is used to protect against:
A) Overvoltage conditions
B) Overfrequency conditions
C) Underfrequency conditions
D) Ground faults
Answer: C

44. In transformer protection, which relay provides protection against faults external to the transformer windings?
A) Differential relay
B) Overcurrent relay
C) Buchholz relay
D) Restricted earth fault relay
Answer: C

45. The ANSI device number 67 refers to:
A) Directional relay
B) Differential relay
C) Voltage balance relay
D) Stator earth fault relay
Answer: A

46. In a generator protection scheme, a loss of field relay is used to protect against:
A) High-voltage conditions
B) Overcurrent conditions
C) Loss of excitation
D) Insulation failures
Answer: C

47. A relay that operates when the current flowing in opposite directions in two conductors exceeds a predetermined value is called:
A) Differential relay
B) Overcurrent relay
C) Directional relay
D) Distance relay
Answer: A

48. The term “inrush current” refers to:
A) Initial current when a transformer is energized
B) Current during a fault condition
C) Current during an overload condition
D) Current in a motor starting sequence
Answer: A

49. In a protection scheme, the term “discrimination” refers to:
A) Relay coordination to ensure that the nearest relay operates first
B) Adjusting relay settings
C) Checking relay health
D) Connecting multiple relays in parallel
Answer: A

50. An auxiliary relay in a protection scheme is used to:
A) Provide primary protection
B) Monitor relay health
C) Initiate alarm signals
D) Provide additional contacts for tripping
Answer: D

Power System Protection and Relaying MCQs

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