Deck 6: Electrical Protection and Circuit Breakers

Question 1

Which component ensures the safety of the line from damage?

A)Relay
B)Circuit breaker
C)Bus bar
D)Current tr

Answer 1

Relay

Question 2

The tripping circuit is_

A)AC
B)DC
C)either AC or DC
D)None of these

Answer 2

either AC or DC

Question 3

Plug setting of a electromagnetic relay can be altered by varying

A)Number of ampere turns
B)Air gap of magnetic path
C)Adjustable back stop
D)None of these

Answer 3

Number of ampere turns

Question 4

the most efficient torque producing actuating structure for the induction type relays is

A)Shaded pole structure
B)Watt hour meter structure
C)Induction cup structure
D)Single induction loop structure

Question 5

If the power factor is zero, the active recovery voltage will be

A)minimum
B)0.5
C)0.707
D)Maximum.

Question 6

Which of the following is not a part of the circuit breaker?

A)Explosion pot
B)Fixed and moving contacts
C)Conservator
D)Operating mechanism.

Question 7

Which of the following circuit breaker will produce the least arc energy?

A)Minimum oil circuit breaker
B)Air blast circuit breaker
C)Plain oil circuit breaker
D)All will produce same energy.

Question 8

For a circuit breaker 'break time' is

A)Same as opening time
B)Opening time + arc duration
C)Opening time + arc duration + resistor current duration.
D)none

Question 9

The breaking capacity of a circuit breaker in MVA (3 phase) is given by

A)Rated service voltage x rated symmetrical current
B)1.1 x rated service voltage x rated symmetrical current
C)(2)1/2 x rated service voltage x rated symmetrical current
D)(3)1/2x rated service voltage x rated symmetrical current.

Question 10

Which relay is used for feeders?

A)MHO relay
B)Translay relay
C)Merz price protection
D)Buchholz relay.

Question 11

Which of the following relays is used on transformers?

A)Buchholz relay
B)MHO relay
C)Merz price relay
D)None of the above.

Question 12

MHO relay is used for

A)Rectifiers
B)Circuit breakers
C)Transmission lines
D)Feeders.

Question 13

Merz-price protection is used on

A)Substations
B)Capacitor bank
C)Induction motor
D)Generators.

Question 14

The values of fault current depend on

A)Voltage at the faulty point
B)Total impedance up to the fault
C)Both (A) and (B) above
D)None of the above

Question 15

The advantage of neutral earthling is

A)Simplified design of earth fault protection
B)Over-voltages due to lightning can be discharged to the earth
C)Freedom from persistent arcing grounds
D)all of the above.

Question 16

The over-voltage surges in power systems may be caused by

A)Lightning
B)Switching
C)Resonance
D)Any of the above.

Question 17

The protection against over-voltage due to lightening is provided by

A)Use of surge diverters
B)Low tower footing resistance
C)Use of overhead ground wires
D)Any of the above.

Question 18

Which of the following is a conducting medium for electric current ?

A)Low temperature gas
B)High temperature gas
C)Dissociated gas
D)Plasma.

Question 19

In circuit-breakers the contact space is ionized by

A)Thermal ionization of gas
B)Thermal emission from surface of contacts
C)Field emission from the surface of contacts
D)Any of the above.

Question 20

Which of the following are air-break switching devices ?

A)Isolator
B)Limit switch
C)Earthling switch
D)All of the above.

Question 21

Which of the following statement about SF6 gas is incorrect?

A)It is non-toxic gas
B)It is non-inflammable
C)It has density 5 times that of air at 200C
D)It has dark yellow color.

Question 22

SF6 gas is transported in

A)Gas cylinders
B)Liquid form in cylinders
C)Solid form in boxes
D)Air cylinders.

Question 23

duringarc extinction SF6 gas

A)Decomposes into S and F ions
B)Decomposes into SF4and SF2
C)Gets oxidized
D)Reduces to SF3.

Question 24

Dielectric strength of SF6 is

A)less than that of air at atmospheric pressure
B)less than that of oil used in OCB
C)more than that of oil used in OCB
D)More at lower pressure and low at higher pressures.

Question 25

Which of the following is the demerit of SF6 circuit breakers?

A)Sealing problem of gas
B)In flux of moisture in the gas system is dangerous
C)Deterioration of quality of circuit breaker affects reliability of circuit breaker
D)All of the above.