Deck 8: Electric Arc and Circuit Breaker Protection

Question 1

The heat produced at the contact point owing to flow of electric current is least affected by_____________________.

A)Temperature of the surrounding medium.
B)Contact resistance.
C)Magnitude of electric current flowing.
D)Duration of flow of current.

Answer 1

Temperature of the surrounding medium.

Question 2

The resistance of an electric arc can be increased by

A)Increasing the concentration of ionised particles.
B)Reducing the arc length.
C)Splitting the arc
D)Increasing the arc cross section.

Answer 2

Splitting the arc

Question 3

By using low resistance method for arc extension what is the value of arc resistance?

A)Arc resistance is zero.
B)Arc resistance is high
C)Arc resistance is low
D)Arc resistance is very high

Answer 3

Arc resistance is low

Question 4

What happens in the arc extinction using high resistance method?

A)Arc resistance is decreased with time.
B)Arc resistance is increased with time.
C)No change it remains same.
D)Arc resistance is kept zero.

Question 5

What is the arc voltage in a circuit breaker?

A)In phase with the arc current.
B)Lagging the arc current by 90°
C)Leading the arc current by 90°
D)Lagging the arcing current by 180°

Question 6

Arcing voltage will be the least in case of

A)Carbon
B)Copper
C)Silver
D)Tungsten

Question 7

How is the initiation of electric arc at the instant of contact separation caused?

A)Thermionic emission of electrons.
B)Field emission of electrons.
C)Both (a) and (b)
D)None of these.

Question 8

The arc resistance depends on which among the following factors?

A)Cross section of the arc
B)Length of the arc
C)Degree of ionization
D)All of the above.

Question 9

Which type of tripping is generally preferred for the circuit breaker?

A)Manual
B)Automatically
C)Depending on the voltage level
D)None of the above

Question 10

Which part of the circuit breaker is helpful in breaking the current?

A)Trip coil.
B)Contacts.
C)Medium
D)Handle.

Question 11

When a fault occurs in a high voltage transmission line, what happens first?

A)Circuit breaker operates then the relay.
B)Relay operates and then the circuit breaker.
C)Relay operates, then successively the isolator and the circuit breaker.
D)Isolator operates, then successively the relay and the circuit breaker.

Question 12

Upto what voltage can the liquid type HRC fuses be used?

A)33 kV
B)132 kV
C)66 kV
D)220 kV

Question 13

What is the main advantage of using a fuse?

A)Cheapest type of protection.
B)Inverse time current characteristics.
C)Current limiting effect under short circuit conditions.
D)All of above.

Question 14

On what basis is the selection of fuse done?

A)Steady load
B)Fluctuating load
C)Both (a) and (b)
D)None of these.

Question 15

Upto what voltage a cartridge type of fuse can be used?

A)400 V
B)11 kV
C)20 kV
D)33 kV

Question 16

In a HRC fuse what is the time between the cut off and the final current zero called?

A)Pre - arcing time.
B)Arcing time.
C)Total operating time.
D)None of these.

Question 17

Which material is used in the liquid type of fuse?

A)SF6
B)Distilled water
C)Carbon tetra chloride.
D)Mineral oil / transformer oil

Question 18

What is the advantage of HRC fuses over Rewirable fuses?

A)High speed operation
B)High rupturing capacity
C)No ageing effect.
D)All of the above.

Question 19

If the strands of the fusing wire are twisted, what happens to the fusing current?

A)Increases
B)Reduces.
C)No change/ remains same
D)Depends on the value of current, increases or decreases.

Question 20

What is the typical value of the pre arcing time?

A)0.1
B)0.01
C)0.001
D)0.0001

Question 21

Outdoor switchgear is generally used for voltage beyond

A)11 KV
B)33 KV
C)66 KV
D)132 KV

Question 22

The least expensive protection for over current in low-voltage system is

A)Rewirable fuse
B)Isolator
C)Circuit breaker
D)Air-break switch

Question 23

Purpose of backup protection is

A)To increase the speed
B)To increase a reach
C)To leave no blind spot
D)To guard against failure of primary

Question 24

We do not require any protection against prime mover failure in case of

A)Turbo generator sets
B)Hydro generator sets
C)Diesel engine driven alternators
D)Back pressure turbo generators

Question 25

For the protection of stator winding of an alternate against internal fault involving ground the relay used is a

A)Biased differential relay
B)Directional over-current relay
C)Plain impedance relay
D)Buchholz relay