Testing And Commissioning Of Electrical Equipment’S Set 6 MCQs

Q1 | On what factor does the operating speed of the relay depend?

Rate of flux built up

Armature core air gap

Spring tension

All of these

Q2 | Protective relays can be designed to respond to ___________.

Light intensity, impedance

Temperature, resistance, reactance

Voltage and current

All of these

Q3 | What is the purpose of back up protection?

To increase the speed

To increase the reach

To leave no blind spot

To guard against failure of primary

Q4 | What is the major cause of the failure of the circuit breaker?

Trip circuit open

Trip latch defective

Spring defective

All of these

Q5 | Why are the isolators used?

Break abnormal current

Making under fault conditions

Breaking the circuit under no load condition

None of the above

Q6 | The isolators used in the transmission lines are capable of breaking

Fault current

No current

Charging current

Load current

Q7 | For which among the following the current ratings are not required?

Circuit breakers

Relays

Isolators

Load break switch

Q8 | What is the making to breaking current ratio for an extra high voltage circuit breaker?

More than 1

Equal to 1

Less than 1

A negative value

Q9 | The breaking capacity of a three phase circuit breaker is given by

Service line voltage * rated symmetrical current in amperes * 10-6 MVA

?3 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

1.1* Service line voltage * rated symmetrical current in amperes * 10-6 MVA

?2 * Service line voltage * rated symmetrical current in amperes * 10-6 MVA

Q10 | Which of the following circuit breaker is highly reliable and has a least maintenance?

Oil circuit breakers

Air blast

Vacuum circuit breakers

SF6 circuit breakers

Q11 | The rating of the circuit breaker is usually determined on the basis of ____________ fault.

Symmetrical

Line to line

Single line to ground

Double line to ground

Q12 | Which among these circuit breakers produce the least arc energy?

Plain oil

Minimum oil

Air blast

Air break

Q13 | A thermal protection switch provides protection against what?

Overload

Temperature

Short circuit

Over voltage

Q14 | What does protective relay provide?

Provide additional safety to the circuit breaker in its operation.

Close the contacts when the actuating quantity attains a certain predetermined value.

Limit the arcing current during the circuit breaker operation.

Earth or ground any stray voltage.

Q15 | What is the main purpose of oil in oil circuit breakers?

Provide insulation

Quenching ar(C)

Provide cooling of contacts.

None of the above

Q16 | What is the advantage of using oil as the arc quenching medium?

Good cooling properties.

High dielectric strength.

Acts as an insulator.

All of these.

Q17 | When does the arc interruption in oil circuit breaker take place?

Contacts apart.

Voltages becomes zero

Current goes through zero

All of the above

Q18 | For rural electrification in India, which circuit breaker is generally used?

Oil

SF6

Vacuum

Air blast

Q19 | Keeping in view the cost and the overall effectiveness, which of the following circuit breaker is best suited for capacitor bank switching?

Vacuum circuit breaker

Air blast CB

SF6

Oil CB

Q20 | To limit current chopping in vacuum circuit breakers, the contact material employed should have the properties of

Low conductivity and high vapour pressure.

Low conductivity and low vapour pressure.

High conductivity and high vapour pressure.

High conductivity and low vapour pressure.

Q21 | SF6 gas is imported in _____________.

Air cylinders

Gas cylinders

Liquid form in cylinders

Solid form.

Q22 | During arc extinction SF6 gas gets converted to which among these?

Gets decomposed to SF4 and SF2

Gets decomposed to S and F

Gets reduced to SF6

Gets oxidized

Q23 | What is the most important property which makes the SF6 very efficient medium for circuit breaking?

Is non toxic and non inflammable.

Has a high dielectric constant.

Has a high breakdown strength

Is highly electronegative gas

Q24 | What is the normal pressure at which the SF6 gas is maintained in the closed position of the breaker?

2 kg / cm2

2.5 kg /cm2

2.8 kg / cm2

3 kg / cm2

Q25 | What is the major drawback of using SF6 circuit breakers?

Sealing problems of the gas.

Ingress of moisture in the gas system – dangerous.

Deterioration of SF6 gas with time.

Both (a) and (b)