Power System Protection — MCQs – EE

1. The main objective of power system protection is to:
(A) Increase power factor
(B) Detect and isolate faulty sections
(C) Improve generation efficiency
(D) Reduce transmission losses

2. A protective relay is designed to:
(A) Sense abnormal conditions and operate a circuit breaker
(B) Regulate system voltage
(C) Control frequency
(D) Balance load currents

3. The main function of a circuit breaker is to:
(A) Interrupt fault currents
(B) Step up voltage
(C) Reduce system losses
(D) Measure current flow

4. Protection systems are required to:
(A) Minimize damage and maintain system stability
(B) Increase transmission line resistance
(C) Reduce the need for maintenance
(D) Improve transformer design

5. The operation of a protective relay is based on:
(A) Electrical quantities like current, voltage, and frequency
(B) Physical displacement
(C) Thermal expansion
(D) Mechanical rotation

6. A fuse provides protection against:
(A) Overcurrent
(B) Overvoltage
(C) Frequency fluctuation
(D) Harmonics

7. Relay coordination ensures that:
(A) The nearest relay to the fault operates first
(B) All relays operate simultaneously
(C) Circuit breakers trip randomly
(D) Relays ignore minor faults

8. Time grading in protection is used to:
(A) Achieve proper sequence of relay operation
(B) Reduce current flow
(C) Improve insulation
(D) Lower voltage

9. The protective device used in a transformer is called:
(A) Buchholz relay
(B) Overcurrent relay
(C) Differential relay
(D) Earth fault relay

10. Overcurrent protection operates when:
(A) Current exceeds a predetermined value
(B) Voltage falls below rated value
(C) Frequency drops
(D) Load decreases suddenly

11. A differential relay operates when:
(A) The difference between two currents exceeds a preset limit
(B) Voltage difference between lines increases
(C) Load fluctuates
(D) Phase angle difference is small

12. Distance protection is mainly used for:
(A) Transmission lines
(B) Transformers
(C) Generators
(D) Motors

13. The operating time of an inverse time overcurrent relay:
(A) Decreases as current increases
(B) Increases as current increases
(C) Is constant for all currents
(D) Depends only on voltage

14. Earth fault protection detects:
(A) Leakage current to ground
(B) Open circuits
(C) Phase reversal
(D) Frequency drift

15. The term “reach” of a distance relay refers to:
(A) The distance along a line it can protect
(B) The voltage sensitivity
(C) The speed of relay operation
(D) The current rating

16. The backup protection operates:
(A) When the primary protection fails
(B) Simultaneously with primary protection
(C) Before primary protection
(D) Only under normal conditions

17. Pilot relaying schemes are generally used for:
(A) Long transmission lines
(B) Distribution feeders
(C) Transformers only
(D) DC systems

18. The main disadvantage of overcurrent protection is:
(A) Time delay in operation for distant faults
(B) High cost
(C) Requirement of high voltage
(D) Need for large space

19. The relay used for protection against unbalanced loading is:
(A) Negative sequence relay
(B) Differential relay
(C) Overcurrent relay
(D) Distance relay

20. In generator protection, the most important protection is:
(A) Differential protection
(B) Earth fault protection
(C) Distance protection
(D) Overvoltage protection

21. A lightning arrester is used to protect equipment from:
(A) High voltage surges
(B) Overcurrent
(C) Mechanical shock
(D) Thermal stress

22. The main purpose of an isolator is to:
(A) Disconnect a section for maintenance
(B) Interrupt fault current
(C) Regulate voltage
(D) Step down power

23. A relay that operates only when two or more conditions are met is called:
(A) Composite relay
(B) Overcurrent relay
(C) Differential relay
(D) Distance relay

24. Static relays use:
(A) Electronic components instead of moving parts
(B) Electromagnetic mechanisms
(C) Mechanical contacts only
(D) Pneumatic devices

25. Numerical relays are based on:
(A) Microprocessor or digital technology
(B) Electromagnetic induction
(C) Analog measurement
(D) Static capacitors

26. The main advantage of numerical relays is:
(A) Multi-function capability and self-testing
(B) High mechanical strength
(C) Simplicity
(D) No maintenance required

27. The zone of protection for a device is defined as:
(A) The portion of the system it can effectively protect
(B) Total system voltage
(C) Line impedance
(D) Relay delay time

28. Busbar protection is generally provided using:
(A) Differential protection
(B) Overcurrent protection
(C) Distance protection
(D) Ground fault relay

29. The relay that responds to change in system frequency is called:
(A) Frequency relay
(B) Directional relay
(C) Distance relay
(D) Thermal relay

30. The overall objective of a protection system is to:
(A) Maintain stability and minimize damage during faults
(B) Reduce line capacitance
(C) Increase load current
(D) Improve transformer efficiency