Switch Gear and Protection 5

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Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Switch Gear and Protection 5

Part 5: List for questions and answers of Switch Gear and Protection


Q1. In axial blast type of CB, expansion of air takes place from ______________

a) High pressure to low pressure

b) Low pressure to high pressure

c) Always in high pressure

d) Always in low pressure


Q2. What is the breaking capacity of the air blast circuit breaker?

a) 5000 MVA

b) 6000 MVA

c) 7000 MVA

d) 10000 MVA


Q3. Why do the SF6 gases have an excellent heat transfer property?

a) Low gaseous viscosity

b) High dielectric strength

c) Higher molecular weight

d) Both (a) and (c)


Q4. 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)


Q5. SF6 is which type of gas?

a) Electro positive

b) Electro negative

c) Both (a) and (b)

d) None of these


Q6. What is the normal pressure at which the SF6 gas is maintained in the closed position of the breaker?

a) 2 kg/cm^2

b) 2.5 kg/cm^2

c) 2.8 kg/cm^2

d) 3 kg/cm^2 


Q7. 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


Q8. 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


Q9. SF6 gas is imported in _____________

a) Air cylinders

b) Gas cylinders

c) Liquid form in cylinders

d) Solid form


Q10. 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


Q11. 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


Q12. For rural electrification in India, which circuit breaker is generally used?

a) Oil

b) SF6

c) Vacuum

d) Air blast 


Q13. 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


Q14. 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


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

a) Provide insulation

b) Quenching arc

c) Provide cooling of contacts

d) None of the above


Q16. 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


Q17.What is / are the main disadvantage / s of using oil as the quenching medium in the circuit breakers?

a) Need periodical replacement

b) Risk of formation of explosive mixture with air

c) Possibility of causing fire hazards

d) All of the above


Q18. A three phase, 33 kV oil circuit breaker is rated 1200 A, 2000 MVA, 3s. What is its symmetrical breaking current?

a) 1200 A

b) 3600 A

c) 35 kA

d) 104.8 kA 


Q19. A thermal protection switch provides protection against what?

a) Overload

b) Temperature

c) Short circuit

d) Over voltage


Q20. Which of the following circuit breakers is used for the railway electrification?

a) Air blast circuit breaker

b) SF6 circuit breaker

c) Bulk oil circuit breaker

d) Minimum oil circuit breaker 


Part 5: List for questions and answers of Switch Gear and Protection


Q1. Answer: a


Q2. Answer: c


Q3. Answer: d


Q4. Answer: d


Q5. Answer: c


Q6. Answer: c


Q7. Answer: d


Q8. Answer: a


Q9. Answer: c


Q10. Answer: a


Q11. Answer: a


Q12. Answer: c


Q13. Answer: c


Q14. Answer: d


Q15. Answer: b


Q16. Answer: b


Q17. Answer: d


Q18. Answer: c


Q19. Answer: a


Q20. Answer: a