Protective Relay MCQ

21. In differential relay, percentage bias is defined the ratio of

  1. difference of current in operating coil to the mean circulating current in restraining coil
  2. mean current in restraining coils to the difference of current in operating coil
  3. difference of current in restraining coils to the mean current in operating c01l
  4. mean current in operating coil to the difference of current in restraining coils
Answer
Answer. a

22. In a biased diferential relay, the bias is defined as the ratio of

  1. fault current and operating coil current
  2. operating coil current and restraining coil current
  3. number of turns of restraining and operating coil
  4. fault current and restraining coil current
Answer
Answer. c

23. The time multiplier for an inverse time relay is

  1. TMS = T x TM
  2. TMS = T/TM
  3. TMS = TM/ T
  4. $TMS = T \times \sqrt{2}T_M$
Answer
Answer. b

24. An over current relay, having a current setting of 125% connected to a supply circuit through a current transformer of ratio 400/5. The pickup value is

  1. 15
  2. 10
  3. 6.25
  4. 25
Answer
Answer. c

25. If the fault current is 2000 A, the relay setting is 50% and CT ratio is 400: 5, then plug setting multiplier will be

  1. 10
  2. 15
  3. 25
  4. 30
Answer
Answer. a

26. Which of the following relay operates when current exceeds a preset value?

  1. Over current relay
  2. Differential relay
  3. Static relay
  4. Instantaneous relay
Answer
Answer. a

27. Buchholz’s relay is

  1. An electronic relay
  2. Mechanical relay
  3. An electromagnetic relay
  4. Gas operated relay
Answer
Answer. d

28. Which type of distance relay in not affected by fault arc resistance?

  1. Mho relay
  2. Differential relay
  3. Reactance relay
  4. Impedance relay
Answer
Answer. c

29. Mho relay is used to protect

  1. Long transmission line
  2. Medium length line
  3. Short length line
  4. All of these
Answer
Answer. a

30. In power system the timings are abbreviated as below

operating time of backup (OTB)
Primary relay time (PRT)
Selective interval time (SIT)
Circuit breaker operating time (CBOT)

Select the correct inequality given below to prevent mal-operation of the protection system

  1. OTB > (PRT+SIT) : SIT > CBOT
  2. OTB < (PRT+SIT) : SIT > CBOT
  3. OTB < (PRT+SIT) : SIT < CBOT
  4. OTB > (PRT+SIT) : SIT > CBOT
Answer
Answer. a
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