Testing And Commissioning Of Electrical Equipment’S Set 7
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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)
Q2 | What is the breaking capacity of the air blast circuit breaker?
- 5000 MVA
- 6000 MVA
- 7000 MVA
- 10000 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.
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
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.
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.
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.
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.
Q9 | What is the maximum current upto which fuses can be used?
- 25 A
- 50 A
- 75 A
- 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
Q11 | For a current upto 10A which material is used as the fusing element?
- Copper
- Silver
- Alloy of lead and tin
- Zinc
Q12 | Which among these is the least expensive protection for over current in lowvoltage system?
- Rewirable fuse.
- Isolator.
- Circuit breaker.
- Air breaker switch.
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.
Q14 | How is the restriking voltage measured?
- RMS value
- Peak value
- Instantaneous value
- Average value
Q15 | What is the interrupting medium in the contactor?
- Air at atmospheric pressure.
- SF6 gas
- Oil
- 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
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.
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)
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).
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
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
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.
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.
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.
Q25 | Which of the following should have low value for the contacts and their material?
- Thermal capacity.
- Contact resistance.
- Thermal conductivity.
- None of above.