Deck 12: Understanding Relays for Power System Protection

Question 1

The domains of power system where directional over current relay is indispensable are

A)In case of parallel feeder protection
B)In case of ring main feeder protection
C)Both A and B
D)None of the above

Answer 1

Both A and B

Question 2

In an inverse definite minimum time, electromagnetic type over current relay, the minimum time feature is achieved because of

A)Saturation of the magnetic circuit
B)Proper mechanical design
C)Appropriate time delay element
D)Electromagnetic damping

Answer 2

Saturation of the magnetic circuit

Question 3

Impedance relay can be used for

A)Phase faults only
B)Earth faults only
C)Both earth and phase faults
D)None of the above

Answer 3

Phase faults only

Question 4

Impedance relay may use

A)Balance beam structure
B)Induction cup structure
C)Shaded pole structure
D)Either A or B

Question 5

An impedance is relay is a

A)Voltage restrained over current relay
B)Voltage restrained directional relay
C)Directional restrained over current relay
D)Directional restrained over voltage relay

Question 6

On transient fault OC and impedance relay

A)Under reaches
B)Over reaches
C)Reach unaffected
D)None of the above

Question 7

Threshold characteristics of a plain impedance relay in a complex Z plane is a

A)Circle passing through origin
B)Circle with the centre at the origin
C)Straight line passing through origin
D)Straight line offset from the origin

Question 8

The structure used in reactance relay is

A)Induction cup
B)Double induction loop
C)Single induction loop
D)Either A or B

Question 9

Reactance relay is normally used for protection against

A)Earth fault only
B)Phase fault only
C)Both earth and phase faults
D)None of the above

Question 10

The operating characteristics of the reactance relay in the complex impedance plane is a

A)Circle with its origin at the centre of the R-X plane
B)Circle passing through the origin
C)Straight line passing through the origin
D)Straight line parallel to the X axis

Question 11

A reactance relay is

A)Voltage restrained overcurrent relay
B)Voltage restrained directional relay
C)Directional restrained overcurrent relay
D)Directional restrained over voltage relay

Question 12

Reactance relays are used for phase fault in.......line

A)Short
B)Medium
C)Long
D)All of the above

Question 13

A differential relay response to

A)Algebraic difference of two or more similar electrical quantities
B)Phasor difference of two or more similar electrical quantities
C)Algebraic difference between two currents
D)Algebraic difference between two voltages

Question 14

Differential relays are used for protection of

A)Feeders
B)Alternators
C)Transformers
D)All of the above

Question 15

Differential relays are used for protection of equipments against

A)Internal faults
B)Over current
C)Reverse current
D)Reverse power

Question 16

In a biased differential relay the bias is defined as a ratio of

A)Number of turns of restraining and operating coil
B)Operating coil current and restraining coil current
C)Fault current and operating coil current
D)Fault current and restraining coil current

Question 17

Both voltage and current signals are required for

A)A plain over current relay
B)A differential relay
C)A directional relay
D)A biased directional relay