Deck 6: Protective Relays and Circuit Breakers for Electrical Systems

Question 1

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

A)Rate of flux built up
B)Armature core air gap
C)Spring tension
D)All of these

Answer 1

All of these

Question 2

Protective relays can be designed to respond to ___________.

A)Light intensity, impedance
B)Temperature, resistance, reactance
C)Voltage and current
D)All of these

Answer 2

All of these

Question 3

What is the purpose of back up protection?

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

Answer 3

To guard against failure of primary

Question 4

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

A)Trip circuit open
B)Trip latch defective
C)Spring defective
D)All of these

Question 5

Why are the isolators used?

A)Break abnormal current
B)Making under fault conditions
C)Breaking the circuit under no load condition
D)None of the above

Question 6

The isolators used in the transmission lines are capable of breaking

A)Fault current
B)No current
C)Charging current
D)Load current

Question 7

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

A)Circuit breakers
B)Relays
C)Isolators
D)Load break switch

Question 8

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

A)More than 1
B)Equal to 1
C)Less than 1
D)A negative value

Question 9

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

A)Oil circuit breakers
B)Air blast
C)Vacuum circuit breakers
D)SF6 circuit breakers

Question 10

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

A)Symmetrical
B)Line to line
C)Single line to ground
D)Double line to ground

Question 11

Which among these circuit breakers produce the least arc energy?

A)Plain oil
B)Minimum oil
C)Air blast
D)Air break

Question 12

A thermal protection switch provides protection against what?

A)Overload
B)Temperature
C)Short circuit
D)Over voltage

Question 13

What does protective relay provide?

A)Provide additional safety to the circuit breaker in its operation.
B)Close the contacts when the actuating quantity attains a certain predetermined value.
C)Limit the arcing current during the circuit breaker operation.
D)Earth or ground any stray voltage.

Question 14

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

A)Provide insulation
B)Quenching ar(C)
C)Provide cooling of contacts.
D)None of the above

Question 15

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

A)Good cooling properties.
B)High dielectric strength.
C)Acts as an insulator.
D)All of these.

Question 16

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

A)Contacts apart.
B)Voltages becomes zero
C)Current goes through zero
D)All of the above

Question 17

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

A)Oil
B)SF6
C)Vacuum
D)Air blast

Question 18

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

A)Vacuum circuit breaker
B)Air blast CB
C)SF6
D)Oil CB

Question 19

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

A)Low conductivity and high vapour pressure.
B)Low conductivity and low vapour pressure.
C)High conductivity and high vapour pressure.
D)High conductivity and low vapour pressure.

Question 20

SF6 gas is imported in _____________.

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

Question 21

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

A)Gets decomposed to SF4 and SF2
B)Gets decomposed to S and F
C)Gets reduced to SF6
D)Gets oxidized

Question 22

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

A)Is non toxic and non inflammable.
B)Has a high dielectric constant.
C)Has a high breakdown strength
D)Is highly electronegative gas

Question 23

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

A)2 kg / cm²
B)2.5 kg /cm²
C)2.8 kg / cm²
D)3 kg / cm²

Question 24

What is the major drawback of using SF6 circuit breakers?

A)Sealing problems of the gas.
B)Ingress of moisture in the gas system - dangerous.
C)Deterioration of SF6 gas with time.
D)Both (a) and (b)