Protective Relaying

Question 1

Per SOO PC 600.12, no unit will be started after any relay operation resulting in targets showing:

Answer 1

Ground fault (64)
Differential (87)
Sudden pressure (63)

Question 2

What are the three major faults that affect power systems?

Answer 2

Three phase
Line to line (phase to phase)
Single line to ground (phase to ground)

Question 3

Primary relaying is:

Answer 3

The first line of defense or protection against electrical or mechanical trouble.

Question 4

Back-up relaying functions only:

Answer 4

When primary relaying fails

Question 5

Auxiliary relays operate:

Answer 5

In response to the opening or closing of its operating circuit
and
to assist another relay or other device in performance of a function.

Question 6

Monitoring or verification relay is used to:

Answer 6

Verify power system conditions with respect to prescribed limits
and
to initiate or permit automatic functions other than opening a circuit breaker during fault conditions

Question 7

The two groups of protective relays:

Answer 7

Primary and backup

Question 8

It is preferable to have adjacent zones of protection:

Answer 8

Overlap

Question 9

Relays operate on two fundamentally different operating principles:

Answer 9

Electromagnetic attraction

Electromagnetic induction

Question 10

Relays that employ the electromagnetic induction principle provide:

Answer 10

A time-delayed operation, which can be adjusted on some, by changing the distance the moving contact must travel

Question 11

An inverse-time curve is one in which:

Answer 11

The operating time becomes less as the magnitude of the actuating quantity is increased

Question 12

Seal-in function:

Answer 12

Prevents arcing
Shunted in parallel
Keeps contacts closed until reset

Question 13

Protective relays have been described as:

Answer 13

The watchdogs of the system

Question 14

Four classes of relays:

Answer 14

1. Auxiliary
2. Protective
3. Regulating
4. Verification

Question 15

Most faults provide several characteristics by which they can be located:

Answer 15

1. Increased current
2. Reduced voltage
3. Fault power always flows towards the fault
4. Temperature rise

Question 16

A contact that is open when the relay is de-energized is termed:

Answer 16

An open “A” contact and a contact that is closed when the relay is de-energized is termed a closed or “B” contact

Question 17

High speed relays operate in:

Answer 17

3 cycles or less

Question 18

The 59N (over-voltage neutral) is used as a separate relay to provide sensitive protection to the grounded neutral because:

Answer 18

It can be set without regard to load current

Current in the neutral transformer produces a voltage in the secondary which operates the relay if the voltage exceeds a predetermined level

Question 19

The 51V ( over-current relay with voltage restraint) is desirable for pumping unit where inrush amps are high because:

Answer 19

It can properly protect the unit against overloads caused by a fault while preventing a trip on a starting amps

Question 20

The induction disc relays are used with:

Answer 20

Resistance Temperature Detectors (RTD) located in the critical temperature ares of the apparatus being used to provide either an alarm or a direct trip action.

Question 21

The most common type of fault is:

Answer 21

Phase to ground