Switchgear and Protection — MCQs – EE

1. The term switchgear refers to:
(A) Combination of switching devices and protective equipment
(B) Only circuit breakers
(C) Only fuses
(D) Transformers and generators

2. The main function of switchgear in a power system is to:
(A) Protect and control electrical circuits and equipment
(B) Increase power generation
(C) Improve power factor
(D) Maintain load frequency

3. The protective devices in switchgear include:
(A) Relays, fuses, and circuit breakers
(B) Motors and alternators
(C) Capacitors and reactors
(D) Transformers and insulators

4. A circuit breaker is used to:
(A) Interrupt the flow of current during abnormal conditions
(B) Step up the voltage
(C) Control reactive power
(D) Adjust system frequency

5. The breaking capacity of a circuit breaker is expressed in:
(A) MVA
(B) kWh
(C) Amperes
(D) Ohms

6. The main purpose of a fuse is to:
(A) Protect equipment from overcurrent
(B) Control voltage
(C) Reduce harmonics
(D) Increase frequency

7. The fuse element is made of materials having:
(A) Low melting point and high conductivity
(B) High melting point
(C) High resistivity
(D) Magnetic properties

8. HRC (High Rupturing Capacity) fuse is used for:
(A) High fault current interruption with minimal arcing
(B) Low voltage DC circuits only
(C) Overvoltage control
(D) Frequency regulation

9. A circuit breaker must be able to:
(A) Make and break current under both normal and fault conditions
(B) Operate only under normal load
(C) Carry no current
(D) Regulate system voltage

10. The arc in a circuit breaker is produced when:
(A) Current-carrying contacts separate under load or fault
(B) Voltage increases suddenly
(C) Load is disconnected manually
(D) Resistance increases

11. The arc in a circuit breaker is extinguished by:
(A) Cooling, lengthening, and splitting of the arc
(B) Increasing voltage
(C) Reducing current
(D) Increasing power factor

12. In oil circuit breakers, the oil acts as:
(A) Both an arc-quenching and insulating medium
(B) Only a cooling agent
(C) Only a conducting medium
(D) A magnetic field enhancer

13. The major disadvantage of an oil circuit breaker is:
(A) Fire hazard and frequent maintenance
(B) High cost
(C) Slow operation
(D) Poor insulation

14. Air blast circuit breakers are mainly used for:
(A) High voltage and rapid reclosing applications
(B) Low voltage domestic circuits
(C) DC traction systems
(D) Capacitor banks

15. In SF₆ circuit breakers, SF₆ gas is used because it:
(A) Has excellent dielectric and arc-quenching properties
(B) Is lighter than air
(C) Is magnetic in nature
(D) Increases contact resistance

16. The main advantage of vacuum circuit breakers is:
(A) Arc extinction occurs at current zero due to absence of ionized particles
(B) They use oil for insulation
(C) They are slow in operation
(D) They require continuous cooling

17. A minimum oil circuit breaker requires:
(A) Less oil than bulk oil circuit breaker for arc extinction
(B) More oil for insulation
(C) No oil at all
(D) External arc suppression device

18. The operating mechanism of a circuit breaker may be:
(A) Spring, pneumatic, or hydraulic
(B) Electric motor only
(C) Manual only
(D) Static relay

19. In power systems, switchgear is generally installed at:
(A) Generating stations, substations, and distribution points
(B) Only at consumer premises
(C) Transformer secondary terminals only
(D) Load end only

20. The relay is a device that:
(A) Detects abnormal conditions and sends signal to circuit breaker
(B) Directly interrupts current
(C) Controls generator output
(D) Converts AC to DC

21. Protective relays are classified according to:
(A) Their operating principle and characteristic
(B) Their physical size
(C) Voltage rating
(D) Installation height

22. The operating time of instantaneous relays is:
(A) Less than 0.1 seconds
(B) 1–2 seconds
(C) Greater than 5 seconds
(D) 10 seconds

23. Differential protection works on the principle of:
(A) Comparing currents entering and leaving a protected zone
(B) Measuring system voltage
(C) Detecting overvoltage
(D) Monitoring frequency changes

24. Distance protection relays are mainly used for:
(A) Transmission line protection
(B) Generator protection
(C) Motor protection
(D) Transformer protection

25. Overcurrent protection is best suited for:
(A) Feeders and distribution lines
(B) Transformers
(C) Generators
(D) Busbars

26. The main purpose of an isolator is to:
(A) Provide visible disconnection for maintenance
(B) Interrupt current during load conditions
(C) Protect against overcurrent
(D) Measure voltage

27. Isolators should be operated:
(A) Only when the circuit is de-energized
(B) Under full load
(C) During short circuits
(D) At maximum current

28. Lightning arresters are installed to:
(A) Protect equipment from voltage surges due to lightning
(B) Improve power factor
(C) Reduce current
(D) Increase voltage regulation

29. The short-time rating of a circuit breaker refers to:
(A) The maximum current it can carry safely for a short duration
(B) Continuous current rating
(C) Normal operating current
(D) Fault voltage rating

30. The overall objective of switchgear and protection is to ensure:
(A) Safety, reliability, and continuity of power supply
(B) Voltage regulation
(C) Frequency control
(D) Energy metering accuracy