7-protection-elements-in-power-distribution-networks

Power System Protection MCQ Part 12

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Power System Protection MCQ Part 12

Which of following statement is correct regarding power system components

Which of following statement is correct regarding power system components:

  1. All components are bilateral
  2. Only rotating machines are bilateral
  3. Both of these
  4. None of these

Correct answer: 4. None of these

Opening one or two phases in a three-phase network will

Opening one or two phases in a three-phase network will:

  1. De-energize the circuit
  2. Create unbalance conditions
  3. Any of above
  4. None of above

Correct answer: 2. Create unbalance conditions

The higher the X/R

The higher the X/R:

  1. The shorter the DC component persists
  2. The longer the DC component persists
  3. X/R and DC components are independent
  4. None of above

Correct answer: 2. The longer the DC component persists

Closing and latching ratings of circuit breakers can be expressed in

Closing and latching ratings of circuit breakers can be expressed in:

  1. RMS amperes
  2. Peak amperes
  3. Both of these
  4. None of these

Correct answer: 3. Both of these

Closing and latching capability ratings of a circuit breaker is defined as the breaker’s ability to withstand the extreme magnetic forces that occur during the first cycle of a short circuit

The formula for Close and Latch (peak or crest) is

The formula for Close and Latch (peak or crest) is:

  1. Close and Latch (peak or crest) = 0.83 × Maximum Symmetrical RMS Fault Current
  2. Close and Latch (peak or crest) = 1.6 × Maximum Symmetrical RMS Fault Current
  3. Close and Latch (peak or crest) = 2.3 × Maximum Symmetrical RMS Fault Current
  4. Close and Latch (peak or crest) = 2.7 × Maximum Symmetrical RMS Fault Current

Correct answer: 4. Close and Latch (peak or crest) = 2.7 × Maximum Symmetrical RMS Fault Current

The current supplied by one-phase conductor is returned to the source by the other two in case of three phase circuits having

The current supplied by one-phase conductor is returned to the source by the other two in case of three phase circuits having:

  1. Positive sequence
  2. Negative sequence
  3. Both of these
  4. None of these

Correct answer: 2. Both of these

In case of presence of fourth conductor serving as return path, the zero-sequence current will

In case of presence of fourth conductor serving as return path, the zero-sequence current will:

  1. Not flow
  2. Flow
  3. Flow but less than 1.732 times
  4. Flow but 4 times more the actual value

Correct answer: 2. Flow

Generally rotating machines will have ________ negative-sequence reactance values than positive-sequence values

Generally rotating machines will have ________ negative-sequence reactance values than positive-sequence values:

  1. Same
  2. Different

Correct answer: 2. Different

The value of first cycle symmetrical fault current at certain bus is 30 kA. What is value of close and latch peak rating of circuit breaker

The value of first cycle symmetrical fault current at certain bus is 30 kA. What is value of close and latch peak rating of circuit breaker:

  1. 42.98 A
  2. 48 A
  3. 52.54 A
  4. 81 A

Correct answer: 2. 48 A

Solution: Close and latch (peak) = 2.7 * 30 = 81 A

The first-cycle symmetrical current is the _________ symmetrical current the system experiences

The first-cycle symmetrical current is the _________ symmetrical current the system experiences:

  1. Minimum
  2. Maximum
  3. Any of above

Correct answer: 2. Maximum

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