NETA Protective Relay Applications 2

Question 1

What is the primary function of a distance relay (21) in transmission line protection?

Accepted Answer

Measure impedance to the fault location

Answer

Measure line current magnitude only

Answer

Monitor voltage at the sending end

Answer

Detect zero-sequence current only

Question 2

Which relay characteristic is best suited for protecting a transformer against internal turn-to-turn faults?

Accepted Answer

Differential relay (87)

Answer

Overcurrent relay (51)

Answer

Distance relay (21)

Answer

Overvoltage relay (59)

Question 3

In a Mho distance relay, the operating characteristic on an R-X diagram is shaped like a:

Accepted Answer

Circle passing through the origin

Answer

Rectangle

Answer

Lens

Answer

Straight line

Question 4

What does the term 'reach' mean in the context of a distance relay?

Accepted Answer

The impedance setting that defines the protected zone boundary

Answer

The maximum voltage the relay can measure

Answer

The relay's operating time in cycles

Answer

The current threshold for instantaneous tripping

Question 5

A pilot protection scheme uses communications between line terminals primarily to:

Accepted Answer

Achieve high-speed tripping for faults anywhere on the protected line

Answer

Increase the relay's current sensitivity

Answer

Reduce the number of CTs required

Answer

Provide backup protection for bus faults

Question 6

Which type of bus protection scheme uses current from all feeders connected to the bus and compares them?

Accepted Answer

Differential bus protection (87B)

Answer

Frame leakage protection

Answer

Directional comparison protection

Answer

Overcurrent bus protection

Question 7

What is the purpose of a check zone in high-impedance bus differential protection?

Accepted Answer

To provide a redundant differential element covering all bus sections

Answer

To measure bus voltage during normal operation

Answer

To detect CT saturation in individual feeder CTs

Answer

To supervise the breaker failure timer