Testing And Commissioning Of Electrical Equipment’S Set 7

Electrical Engineering

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This set of Testing and Commissioning of Electrical Equipment’s Multiple Choice Questions & Answers (MCQs) focuses on Testing And Commissioning Of Electrical Equipment’S Set 7

Q1 | Why do the SF6 gases have an excellent heat transfer property?
  • Low gaseous viscosity.
  • High dielectric strength.
  • Higher molecular weight.
  • Both (a) and (c)
Answer: Both (a) and (c)
Q2 | What is the breaking capacity of the air blast circuit breaker?
  • 5000 MVA
  • 6000 MVA
  • 7000 MVA
  • 10000 MVA
Answer: 7000 MVA
Q3 | In axial blast type of CB, expansion of air takes place from ______________.
  • High pressure to low pressure.
  • Low pressure to high pressure.
  • Always in high pressure.
  • Always in low pressure.
Answer: High pressure to low pressure.
Q4 | The air blast circuit breakers for 400 kV systems are designed to operate in howmuch time?
  • 0.1 s
  • 0.5 s
  • 50 ms
  • 100µs
Answer: 50 ms
Q5 | What is the type of air blast in cross blast type CB?
  • The blast of air is along the ar(C)
  • The blast of air cuts across the ar(C)
  • Both (a) and (b)
  • None of the above.
Answer: The blast of air cuts across the ar(C)
Q6 | Why is the resistance switching used in a air blast circuit breaker?
  • Reduce the magnitude of fault current.
  • Control the CB operating time.
  • Damp out the fast transient.
  • Change the fault current power factor.
Answer: Damp out the fast transient.
Q7 | When using air blast circuit breaker, current chopping is a phenomenon observedwhen
  • A long overhead line is switched off.
  • A bank of capacitors is switched off.
  • A transformer on no load is switched off.
  • A heavy load is switched off.
Answer: A transformer on no load is switched off.
Q8 | Which type of air is used in air blast circuit breaker?
  • Ionised air
  • Air free from moisture
  • Air should have least CO2
  • Air must have oil mist.
Answer: Air free from moisture
Q9 | What is the maximum current upto which fuses can be used?
  • 25 A
  • 50 A
  • 75 A
  • 100 A
Answer: 100 A
Q10 | What is fusing factor?
  • The ratio of current rating of the fuse to the minimum fusing current
  • The ratio of minimum fusing current to the current rating of the fuse
  • The ratio of maximum fusing current to the current rating of the fuse
  • The ratio of minimum fusing current to the voltage rating of the fuse
Answer: The ratio of current rating of the fuse to the minimum fusing current
Q11 | For a current upto 10A which material is used as the fusing element?
  • Copper
  • Silver
  • Alloy of lead and tin
  • Zinc
Answer: Alloy of lead and tin
Q12 | Which among these is the least expensive protection for over current in lowvoltage system?
  • Rewirable fuse.
  • Isolator.
  • Circuit breaker.
  • Air breaker switch.
Answer: Rewirable fuse.
Q13 | Which among the following statement is true related to fuse?
  • Greater the current smaller is the time taken by the fuse to blow out.
  • Greater the current greater is the time taken by the fuse to blow out.
  • The current is directly proportion to the blow out time of fuse.
  • Is dependent on the temperature and atmospheric conditions.
Answer: Greater the current smaller is the time taken by the fuse to blow out.
Q14 | How is the restriking voltage measured?
  • RMS value
  • Peak value
  • Instantaneous value
  • Average value
Answer: Peak value
Q15 | What is the interrupting medium in the contactor?
  • Air at atmospheric pressure.
  • SF6 gas
  • Oil
  • All of the above.
Answer: All of the above.
Q16 | Recovery voltage is the value of rms voltage that reappears across the poles of acircuit breaker before_______________
  • Restriking voltage
  • Final arc extinction
  • Rise of voltage
  • All of the above
Answer: Final arc extinction
Q17 | Why is it difficult to interrupt a capacitive circuit?
  • The current has a leading power factor.
  • The restriking voltage can be high.
  • Current magnitude is very small.
  • Stored energy in the capacitor is very high.
Answer: The restriking voltage can be high.
Q18 | Rate of rise of restriking voltage depend on_____________?
  • Type of circuit breaker.
  • Capacitance of the system.
  • Inductance of the system.
  • Both (b) and (c)
Answer: Both (b) and (c)
Q19 | On what factor does the rate of rise of restriking voltage (RRRV) depend?
  • System voltage.
  • Circuit power factor only
  • Switching conditions
  • Both (b) and (c).
Answer: Both (b) and (c).
Q20 | In a circuit breaker, the active recovery voltage depends upon which amongthese?
  • Circuit conditions.
  • Power factor.
  • Both (a) and (b)
  • None of the above
Answer: Both (a) and (b)
Q21 | What is restriking voltage?
  • The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.
  • The transient voltage that appears across the circuit breaker contacts at the end of arc extinction.
  • Both (a) and (b)
  • None of the above
Answer: The transient voltage that appears across the circuit breaker contacts at the instant of arc extinction.
Q22 | For a high speed circuit breaker what will the total clearing time?
  • Few minutes.
  • Few seconds.
  • 1 to 2 cycles.
  • 5 to 20 cycles.
Answer: 1 to 2 cycles.
Q23 | The interrupting time of a circuit breaker is the period between the instant of_________.
  • Initiation of short circuit and the arc extinction on an opening operation.
  • Energizing the trip circuit and the arc extension on an opening operation.
  • Initiation of short circuit and the parting of primary arc contacts.
  • Energizing of the trip circuit and the parting of primary arc contacts.
Answer: Energizing the trip circuit and the arc extension on an opening operation.
Q24 | In a circuit breaker, ionisation is facilitated by_________________.
  • Increase in field strength.
  • Increase in mean free length.
  • High temperature of the surrounding medium.
  • All of the above.
Answer: All of the above.
Q25 | Which of the following should have low value for the contacts and their material?
  • Thermal capacity.
  • Contact resistance.
  • Thermal conductivity.
  • None of above.
Answer: Contact resistance.
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