power-system-protection-mcqs

Power System Protection MCQs Part 3

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a. The rate of rise of restriking voltage is usually expressed in terms of:

  1. V / s
  2. kV / ms
  3. kV / µs
  4. MV/ns

Correct answer: 3. kV / µs

b. It is desired to chop 20 A current in a circuit having L = 4 mH, C = 0.2 µC. Find the induced voltage.

  1. 10 kV
  2. 3.72 kV
  3. 2.8 kV
  4. 1.7 kV

Correct answer: 3. 2.8 kV

Solution = i √(L/C) = 20 A * √(4 mH/0.2 uC) = 2.8 kV

c. Fault diverter is actually a:

  1. Fuse
  2. Circuit breaker
  3. Relay
  4. Switch

Correct answer 4. Switch

3. The fault diverter is actually a fast switch.

d. The major advantage associated with the static digital relay is:

  1. Less sensitive
  2. Performance speed is slow
  3. It is expensive
  4. It is not accurate

Correct answer: 3. It is expensive

e. Fusing factor of a fuse is mathematically defined by the equation:

  1. Current rating of fuse * 4.44
  2. 1/Current rating of the fuse
  3. Min fusing current / Current rating of the fuse
  4. Min fusing current * Current rating of the fuse

Correct answer: 3. Min fusing current / Current rating of the fuse

f. The correct statement about Sulphur Hexaflouride gas:

  1. It provides free electrons to the breaker
  2. It absorbs free electrons
  3. It increases current flow the through the arc
  4. None of these

Correct answer: 2. It absorbs free electrons

g. The correct equation which explains the breaking capacity of single phase circuit breaker:

  1. V × I × 10−1 MVA
  2. V × I × 10−3 MVA
  3. V × I × 10−6 MVA
  4. V × I × 10−9 MVA

Correct answer: 3. V × I × 10−6 MVA

h. The __________ the current, the ___________ is the time required by fuse to blow up:

  1. Greater, smaller
  2. Greater, Greater
  3. Smaller, Smaller
  4. All of these are possible

Correct answer: 1. Greater, smaller

i. Usually the earth relays have ___________ current settings:

  1. Lower
  2. Higher
  3. Both
  4. None

Correct answer: 1. Lower

j. The correct equation which explains the breaking capacity of 3 phase circuit breaker:

  1. √3 × V × I × 10−1 MVA
  2. √3 × V × I × 10−3 MVA
  3. √3 × V × I × 10−6 MVA
  4. √3 × V × I × 10−9 MVA

Correct answer: 3. √3 × V × I × 10−6 MVA

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