Deck 4: Electrical Protection and Circuit Breakers

Question 1

Which of the following circuit breakers has high reliability and minimum maintenance ?

A)Air blast circuit breakers
B)Circuit breaker with SF6 gas
C)Vacuum circuit breakers
D)Oil circuit breakers

Answer 1

Circuit breaker with SF6 gas

Question 2

Arc in a circuit breaker is interrupted at

A)zero current
B)maximum current
C)minimum voltage
D)maximum voltage

Answer 2

zero current

Question 3

transmission line has reflection coefficient as one.

A)Open circuit
B)Short-circuit
C)Long
D)None of the above

Answer 3

Open circuit

Question 4

What will be the reflection co-efficient of the wave of load connected to transmission line if surge impedance of the line is equal to load ?

A)Zero
B)Unity
C)Infinity
D)None of the above

Question 5

The inverse definite mean time relays are used for over current and earth fault protection of transformer against

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

Question 6

Over voltage protection is recommended for

A)hydro-electric generators
B)steam turbine generators
C)gas turbine generators
D)all of the above

Question 7

Air blast circuit breakers for 400 kV power system are designed to operate in

A)100 microsecond
B)50 millisecond
C)0.5 sec
D)0.1 sec

Question 8

Overfluxing protection is recommended for

A)distribution transformer
B)generator transformer of the power plant
C)auto-transformer of the power plant
D)station tr

Question 9

Series capacitors are used to

A)compensate for line inductive reactance
B)compensate for line capacitive reactance
C)improve line voltage
D)none of the above

Question 10

Admittance relay is _______ relay.

A)impedance
B)directional
C)non-directional
D)none of the above

Question 11

The material used for fuse must have

A)low melting point and high specific resistance
B)low melting point and -low specific resistance
C)high melting point and low specific resistance
D)low melting point and any specific resistance

Question 12

If the fault occurs near the impedance relay, the VII ratio will be

A)constant for all distances
B)lower than that of if fault occurs away from the relay
C)higher than that of if fault occurs away from the relay
D)none of the above

Question 13

The torque produced in induction type relay (shaded pole structure) is

A)inversely proportional to the current
B)inversely proportional to the square of the current
C)proportional to the current
D)proportional to square of the current

Question 14

The steady state stability of the power system can be increased by

A)connecting lines in parallel
B)connecting lines in series
C)using machines of high impedance
D)reducing the excitation of machines

Question 15

The inductive interference between power and communication line can be minimized by

A)transposition of the power line
B)transposition of the communication line
C)both (a) and (b)
D)increasing the distance between the conductors

Question 16

The power loss is an important factor for the design of

A)transmission line
B)motor
C)generator
D)feeder

Question 17

A fuse is connected

A)in series with circuit
B)in parallel with circuit
C)either in series or in parallel with circuit
D)none of the above

Question 18

H.R.C. fuse, as compared to a rewirable fuse, has

A)no ageing effect
B)high speed of operation
C)high rupturing capacity
D)all of the above

Question 19

The fuse rating is expressed in terms of

A)current
B)voltage
C)VAR
D)kVA

Question 20

The fuse blows off by

A)burning
B)arcing
C)melting
D)none of the above

Question 21

On which of the following effects of electric current a fuse operates ?

A)Photoelectric effect
B)Electrostatic effect
C)Heating effect
D)Magnetic effect

Question 22

An isolator is installed

A)to operate the relay of circuit breaker
B)as a substitute for circuit breaker
C)always independent of the position of circuit breaker
D)generally on both sides of a circuit breaker

Question 23

A fuse in a motor circuit provides protection against

A)overload
B)short-circuit and overload
C)open circuit, short-circuit and overload
D)none of the above

Question 24

Protection by fuses is generally not used beyond

A)20 A
B)50 A
C)100 A
D)200 A

Question 25

A fuse is never inserted in

A)neutral wire
B)negative of D.C. circuit
C)positive of D.C. circuit
D)phase dine