Deck 1: Electrical Protection and Circuit Breakers

Question 1

The main function of a fuse is to

A)protect the line
B)open the circuit
C)protect the appliance
D)prevent excessive currents

Answer 1

prevent excessive currents

Question 2

On which of the following routine tests are conducted ?

A)Oil circuit breakers
B)Air blast circuit breakers
C)Minimum oil circuit breakers
D)All of the above

Answer 2

All of the above

Question 3

SF6 gas

A)is yellow in colour
B)is lighter than air
C)is nontoxic
D)has pungent small

Answer 3

is nontoxic

Question 4

The arcing contacts in a circuit breaker are made of

A)copper tungsten alloy
B)porcelain
C)electrolytic copper
D)aluminium alloy

Question 5

Which of the following medium is employed for extinction of arc in air circuit breaker ?

A)Water
B)Oil
C)Air
D)SF6

Question 6

With which of the following, a circuit breaker must be equipped for remote operation ?

A)Inverse time trip
B)Time-delay trip
C)Shunt trip
D)None of the above

Question 7

Fault diverters are basically

A)fuses
B)relays
C)fast switches
D)circuit breakers

Question 8

A thermal protection switch can protect against

A)short-circuit
B)temperature
C)overload
D)over voltage

Question 9

Arc in a circuit behaves as

A)a capackive reactance
B)an inductive reactance
C)a resistance increasing with voltage rise across the arc
D)a resistance decreasing with voltage rise across the arc

Question 10

Thermal circuit breaker has

A)delayed trip action
B)instantaneous trip action
C)both of the above
D)none of the above

Question 11

Thermal overload relays are used to protect the motor against over current due to

A)short-circuits
B)heavy loads
C)grounds
D)all of the above

Question 12

Magnetic circuit breaker has ______ trip action.

A)delayed
B)instantaneous
C)both of the above
D)none of the above

Question 13

D.C. shunt relays are made of

A)few turns of thin wire
B)few turns of thick wire
C)many turns of thin wire
D)many turns of thick wire

Question 14

The relay operating speed depends upon

A)the spring tension
B)the rate of flux built up
C)armature core air gap
D)all of the above

Question 15

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should

A)have low contact resistance
B)be clean and smooth
C)be of sufficient size and proper shape
D)have all above properties

Question 16

Circuit breakers usually operate under

A)transient state of short-circuit current
B)sub-transient state of short-circuit current
C)steady state of short-circuit current
D)after D.C. component has ceased

Question 17

Circuit breakers are essentially

A)current carrying contacts called electrodes
B)arc extinguishers
C)circuits to break the system
D)transformers to isolate the two systems

Question 18

The current zero interruption, in oil and air blast circuit breakers, is achieved by

A)lengthening of the gap
B)cooling and blast effect
C)both (A) and (B)
D)deionizing the oil with forced air

Question 19

Air blast circuit breaker is used for

A)over currents
B)short duty
C)intermittant duty
D)repeated duty

Question 20

An efficient and a well designed protective relaying should have

A)good selectivity and reliability
B)economy and simplicity
C)high speed and selectivity
D)all of the above

Question 21

Burden of a protective relay is the power

A)required to operate the circuit breaker
B)absorbed by the circuit of relay
C)developed by the relay circuit
D)none of the above

Question 22

Directional relays are based on flow of

A)power
B)current
C)voltage wave
D)all of the above

Question 23

A differential relay measures the vector difference between

A)two currents
B)two voltages
C)two or more similar electrical quantities
D)none of the above

Question 24

A transmission line is protected by

A)inrush protection
B)distance protection
C)time graded and current graded over current protection
D)both (B) and (C)

Question 25

Large internal faults are protected by

A)merz price percentage differential protection
B)mho and ohm relays
C)horn gaps and temperature relays
D)earth fault and positive sequence relays