Question 1

SF6 gas is imported in _____________.

Accepted Answer

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

Question 2

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

Accepted Answer

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. A

Question 3

A thermal protection switch provides protection against what?

Accepted Answer

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

Question 4

What is the major drawback of using SF6 circuit breakers?

Accepted Answer

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)

Question 5

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

Accepted Answer

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 6

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

Accepted Answer

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

Question 7

What does protective relay provide?

Accepted Answer

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 8

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

Accepted Answer

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

Question 9

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

Accepted Answer

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

Question 10

Why are the isolators used?

Accepted Answer

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

Question 11

What is the purpose of back up protection?

Accepted Answer

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

Question 12

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

Accepted Answer

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

Question 13

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

Accepted Answer

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

Question 14

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

Accepted Answer

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

Question 15

Protective relays can be designed to respond to ___________.

Accepted Answer

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

Question 16

The isolators used in the transmission lines are capable of breaking

Accepted Answer

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

Question 17

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

Accepted Answer

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

Question 18

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

Accepted Answer

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

Question 19

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

Accepted Answer

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

Question 20

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

Accepted Answer

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

Exam 6: Protective Relays and Circuit Breakers for Electrical Systems