Power System Protection MCQs Part 2

a. In case of fault it is often desired that frame leakage protection should trip:

  1. Half the installed breakers
  2. Only one breaker
  3. All connected breakers
  4. Two breakers

Correct answer: 3. All connected breakers

b. The correct equation for an effectively grounded system is:

  1. X0/X1 < 3.0
  2. X0/X1 > 3.0
  3. X0/X1 > 2.0
  4. 3.0 < X0/X1< 9.0

Correct answer: 1. X0/X1 < 3.0

c. Buchholz relay is used to protect:

  1. Alternator
  2. Induction Motors
  3. Synchronous motors
  4. Transformers

Correct answer: 4. Transformers

d. Generally, the carrier current protection scheme is recommended for:

  1. HV cables
  2. HV transmission lines
  3. Both of these
  4. None of these

Correct answer: 2. HV transmission lines

e. SF6 gas is ____________:

  1. Highly inflammable
  2. Non-inflammable

Correct answer: 3. Non-inflammable

f. The under-voltage relay is recommended for:

  1. Transformers
  2. Motors
  3. Feeder
  4. Busbars

Correct answer: 2. Motors

g. ____________________ is/are an instantaneous relay/s:

  1. PMMC type
  2. Shaded pole type
  3. Both of these
  4. None of these

Correct answer: 1. PMMC type

h. Statement: SF6 circuit breakers have very short arcing time.

Utterance: SF6 circuit breakers are costly.

  1. Both statement and utterance are correct
  2. Both are wrong
  3. The statement is correct, the utterance is wrong
  4. The statement is wrong, the utterance is correct

Correct answer: 1. Both statement and utterance are correct

i. Plug setting multiplier is defined as the ratio of:

  1. Fault current in relay coil x Pick up current
  2. Fault current in relay coil / Pick up current
  3. Fault current in relay coil x Transformer secondary turns
  4. Fault current in relay coil / Transformer secondary turns

Correct answer: 2. Fault current in relay coil / Pick up current

j. High-speed circuit breakers result in:

  1. Increased stability of power systems
  2. Decreased stability of the power system

Correct answer: 2. Decreased stability of the power system

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