Switch Gear and Protection Mid - I, September - 2014

1.A circuit breaker is
  • Power factor correcting device
  • a device to neutralize the effect of transients
  • a waveform correcting device
  • a current interrupting device
Answer: D
2.The normal frequency rms voltage that appears across the breaker poles after final arc extinction has occurred, is
  • recovery voltage
  • restriking voltage
  • supply voltage
  • peak voltage
Answer: A
3.Which of the following circuit breakers is preferred for EHT application
  • air blast circuit breakers
  • minimum oil circuit breakers
  • bulk oil circuit breakers
  • sf6 oil circuit breakers
Answer: D
4.In air blast circuit breakers, the pressure of air is of the order of
  • 100 mm hg
  • 1 kg/cm2
  • 20 to 30 kg/cm2
  • 200 to 300 kg/cm2
Answer: C
5.An automatic device that operates at preset values is known as
  • mercury switch
  • relay
  • fuse
  • contactor
Answer: B
6.Which of the following relays is used on transformers ?
  • buchholz relay
  • mho relay
  • merz price relay
  • none of the above
Answer: A
7.Differential protection principle is used in the protection of
  • generators
  • transformers
  • feeders
  • all of the above.
Answer: D
8.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
Answer: D
9.Unbalanced 3-phase stator currents cause
  • double frequency currents in the rotor
  • healing of rotor
  • vibrations
  • all of the above.
Answer: D
10.In large generators protection provided against external faults is
  • biased differential protection
  • sensitive earth fault protection
  • inter-turn fault protection
  • all of the above.
Answer: D
11.Over fluxing protection is recommended for _________________________
Answer: Generator of the power plant
12.For greatest sensitivity of differential relaying, the CT primary-current rating would have to be ____________________________
Answer: Equal to the generators rated full-load current
13.A relay which responds to increase in current is known as ____________________ relay.
Answer: Over current
14.Earth fault relays are _____________________
Answer: Directional relays
15.SF6 gas Properties are _____________________
Answer: Is non-inflammable, Non Toxic
16.In a vacuum circuit breaker, the vacuum is of the order of ____________________
Answer: 10-9mmhg
17.Low voltage circuit breakers have rated voltage of less than ___________________
Answer: 1000V
18.The voltage across the contacts of the circuit breaker is called __________________
Answer: Arc Voltage
19.The breaking capacity of a circuit breaker in MVA (3 phase) is given by ________________
Answer: (3)1/2x rated service voltage x rated symmetrical current
20.PSM Means _______________________
Answer: Plug Setting Multiplier