Switchgear protections

1. In order that current should flow without causing excessive heating or voltage drop, the relay contacts should

Have low contact resistance
Be clean and smooth
Be of sufficient size and proper shape
Have all above properties

Detailed SolutionIn order that current should flow without causing excessive heating or voltage drop, the relay contacts should

2. Arc in a circuit breaker is interrupted at

zero current
maximum current
minimum voltage
maximum voltage

Detailed SolutionArc in a circuit breaker is interrupted at

3. The relay with inverse time characteristic will operate within

1.5 sec
5 to 10 sec
5 to 20 sec
20 to 30 sec E. none of the above

Detailed SolutionThe relay with inverse time characteristic will operate within

4. Which of the following circuit breakers has high reliability and minimum maintenance ?

Air blast circuit breakers
Circuit breaker with SF6 gas
Vacuum circuit breakers
Oil circuit breakers

Detailed SolutionWhich of the following circuit breakers has high reliability and minimum maintenance ?

5. The interaction between a transmission line and communication line is minimized by

transposing transmission as well as communication lines
increasing the height of the trans-mission line tower
increasing the distance between the two lines
all of the above

Detailed SolutionThe interaction between a transmission line and communication line is minimized by

6. Oil switches are employed for

low currents circuits
low voltages circuits
high voltages and large currents circuits
all circuits

Detailed SolutionOil switches are employed for

7. Which of the following devices will receive voltage surge first travelling on the transmission line ?

Lightning arresters
Relays
Step-down transformer
Switchgear

Detailed SolutionWhich of the following devices will receive voltage surge first travelling on the transmission line ?

8. For cost and safety, the outdoor substations are installed for voltages above

11 kV
33 kV
60 kV
110 kV

Detailed SolutionFor cost and safety, the outdoor substations are installed for voltages above

9. An efficient and a well designed protective relaying should have

good selectivity and reliability
economy and simplicity
high speed and selectivity
all of the above

Detailed SolutionAn efficient and a well designed protective relaying should have

10. On which of the following effects of electric current a fuse operates?

Photoelectric effect
Electrostatic effect
Heating effect
Magnetic effect

Detailed SolutionOn which of the following effects of electric current a fuse operates?

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