Testing And Commissioning Of Electrical Equipment’S Set 8 MCQs

Q1 | The heat produced at the contact point owing to flow of electric current is leastaffected by_____________________.

Temperature of the surrounding medium.

Contact resistance.

Magnitude of electric current flowing.

Duration of flow of current.

Q2 | The resistance of an electric arc can be increased by

Increasing the concentration of ionised particles.

Reducing the arc length.

Splitting the ar(C)

Increasing the arc cross section.

Q3 | By using low resistance method for arc extension what is the value of arcresistance?

Arc resistance is zero.

Arc resistance is high

Arc resistance is low

Arc resistance is very high

Q4 | What happens in the arc extinction using high resistance method?

Arc resistance is decreased with time.

Arc resistance is increased with time.

No change it remains same.

Arc resistance is kept zero.

Q5 | What is the arc voltage in a circuit breaker?

In phase with the arc current.

Lagging the arc current by 90°

Leading the arc current by 90°

Lagging the arcing current by 180°

Q6 | Arcing voltage will be the least in case of

Carbon

Copper

Silver

Tungsten

Q7 | How is the initiation of electric arc at the instant of contact separation caused?

Thermionic emission of electrons.

Field emission of electrons.

Both (a) and (b)

None of these.

Q8 | The arc resistance depends on which among the following factors?

Cross section of the ar(C)

Length of the ar(C)

Degree of ionization

All of the above.

Q9 | Which type of tripping is generally preferred for the circuit breaker?

Manual

Automatically

Depending on the voltage level

None of the above

Q10 | Which part of the circuit breaker is helpful in breaking the current?

Trip coil.

Contacts.

Medium

Handle.

Q11 | When a fault occurs in a high voltage transmission line, what happens first?

Circuit breaker operates then the relay.

Relay operates and then the circuit breaker.

Relay operates, then successively the isolator and the circuit breaker.

Isolator operates, then successively the relay and the circuit breaker.

Q12 | Upto what voltage can the liquid type HRC fuses be used?

33 kV

132 kV

66 kV

220 kV

Q13 | What is the main advantage of using a fuse?

Cheapest type of protection.

Inverse time current characteristics.

Current limiting effect under short circuit conditions.

All of above.

Q14 | On what basis is the selection of fuse done?

Steady loa(D)

Fluctuating loa(D)

Both (a) and (b)

None of these.

Q15 | Upto what voltage a cartridge type of fuse can be used?

400 V

11 kV

20 kV

33 kV

Q16 | In a HRC fuse what is the time between the cut off and the final current zerocalled?

Pre - arcing time.

Arcing time.

Total operating time.

None of these.

Q17 | Which material is used in the liquid type of fuse?

SF6

Distilled water

Carbon tetra chloride.

Mineral oil / transformer oil

Q18 | What is the advantage of HRC fuses over Rewirable fuses?

High speed operation

High rupturing capacity

No ageing effect.

All of the above.

Q19 | If the strands of the fusing wire are twisted, what happens to the fusing current?

Increases

Reduces.

No change/ remains same

Depends on the value of current, increases or decreases.

Q20 | What is the typical value of the pre arcing time?

0.1

0.01

0.001

0.0001

Q21 | Outdoor switchgear is generally used for voltage beyond

11 KV

33 KV

66 KV

132 KV

Q22 | The least expensive protection for over current in low-voltage system is

Rewirable fuse

Isolator

Circuit breaker

Air-break switch

Q23 | Purpose of backup protection is

To increase the speed

To increase a reach

To leave no blind spot

To guard against failure of primary

Q24 | We do not require any protection against prime mover failure in case of

Turbo generator sets

Hydro generator sets

Diesel engine driven alternators

Back pressure turbo generators

Q25 | For the protection of stator winding of an alternate against internal fault involvingground the relay used is a

Biased differential relay

Directional over-current relay

Plain impedance relay

Buchholz relay