Switchgear and Protection Objective Questions Answers

1. Relay contacts are normally made up of:
a) Silver contacts
b) Copper contacts
c) Aluminium contacts
d) Lead contacts

A

2. The most efficient torque-producing actuating structure for induction type relays is:
a) Shaded pole structure
b) Watt-hour meter structure
c) Induction cup structure
d) Single induction cup structure

C

3. Impedance relays can be used for:
a) Phase faults only
b) Earth faults only
c) Both earth and phase faults
d) None of the above

C

4. Sparking between the contacts can be reduced by inserting:
a) A capacitor in parallel with the contacts
b) A capacitor in series with the contacts
c) A resistor in the line
d) A reactor in the line

A

5. The contact resistance is least affected by:
a) Shape of the contact faces
b) Ambient temperature
c) Mechanical forces applied
d) Amount of surface commutation

B

6. The arc voltage produced in an ac circuit breaker is always:
a) In phase with the arc current
b) Lagging the arc current by 90 deg
c) Leading the arc current by 90 deg
d) In phase opposition with the arc current

A

7. Breaking capacity of the circuit breaker is usually expressed in:
a) MVA
b) MW
c) Kilo-amperes
d) kV

A

8. Which of the following circuit breakers produce least arc energy:
a) Plain oil
b) Minimum oil
c) Air blast
d) Air break

C

9. Arc chutes are used in:
a) Oil circuit breaker
b) Vacuum circuit breakers
c) SF6 circuit breakers
d) Air blast circuit breakers

D

10. A thermal protection switch is used to provide protection against:
a) Over load
b) Temperature
c) Short circuit
d) Over voltage

A