Deck 11: Relaying Schemes and Techniques for Electrical Equipment Protection

Question 1

Where severe synchronising swing occur, the relay employed is

A)Impedance relay
B)Mho relay
C)Reactance relay
D)Induction relay

Answer 1

Mho relay

Question 2

For the protection of lines against faults involving variable fault resistance, the preferred relaying scheme is a

A)Plain impedance relay
B)Directional over-current relay
C)Mho relay
D)Reactance relay

Answer 2

Reactance relay

Question 3

For ground fault we prefer

A)Plain impedance relay
B)Directional over current relay
C)Mho relay
D)Reactance relay

Answer 3

Reactance relay

Question 4

Admittance relay

A)Nondirectional relay
B)Directional relay
C)Differential relay
D)None of the above

Question 5

The relay used for feeder protection is

A)Under voltage relay
B)Translay relay
C)Thermal relay
D)Buchholz relay

Question 6

Which relay is used to detect and protect internal fault in a transformer ?

A)Buchholz relay
B)Directional relay
C)Thermal relay
D)Distance relay

Question 7

Which one of the following relay has the capability of anticipating the possible major fault in a transformer ?

A)Over-current relay
B)Differential relay
C)Buchholz relay
D)Over fluxing relay

Question 8

Zero sequence current is used for relaying purpose only in the case of

A)Phase over current really
B)Phase impedance relay
C)Ground over current relay
D)Ground impedance relay

Question 9

To prevent mal operation of differentially connected relay while energising a transformer, the relay restraining coil is biased with

A)Second harmonic current
B)Third harmonic current
C)Fifth harmonic current
D)Seventh harmonic current

Question 10

How many relays are used to detect interphase fault of a three line system?

A)One
B)Two
C)Three
D)Six

Question 11

Which is the main relay for protecting up to 90% of the transmission line-length in the forward direction?

A)Directional over current relay
B)Mho relay
C)Carrier current protective relay
D)Impedance relay

Question 12

For protection of parallel feeders fed from one end, the relays required are

A)Nondirectional relays at the source end and directional relay at the load end
B)Nondirectional relay at both ends
C)Directional relay at source end and nondirectional relay at load end
D)Directional relay at both ends

Question 13

Relays can be designed to respond to changes in

A)Resistance, reactance or impedance
B)Voltage and current
C)Light intensity
D)All of the above

Question 14

DC shunt relays are made of

A)Few turns of thin wire
B)Few turns of thick wire
C)Many turns of thin wire
D)Many turns of thick wire

Question 15

In order that current should flow without causing excessive heating or voltage drop, the relay contacts should

A)Have low contact resistance
B)Be clean and smooth
C)Be of sufficient size and proper shape
D)Have all above properties

Question 16

Interruption of large currents by relay requires

A)Arc suppressing blow out coils
B)Wide separation of the open contacts
C)High speed opening of contacts
D)All of the above

Question 17

To protect most of the electrical equipment handling low power, the types of relays used are

A)Thermocouple
B)Electronic and bimetallic
C)Both A and B
D)None of the above

Question 18

............. Relays are used for phase faults on long line

A)Impedance
B)Reactance
C)Either of the above
D)None of the above

Question 19

........ Relays is preferred for phase fault on short transmission line

A)Induction type
B)Reactance
C)Impedance
D)None of the above

Question 20

The under voltage relay can be used for

A)Generators
B)Bus bars
C)Transformers
D)All of the above

Question 21

The single phasing relays are used for the protection of

A)Single phase motors only
B)Two phase motors only
C)Two single phase motor running in parallel
D)Three phase motors

Question 22

The inverse definite mean time relays are used for over current and earth fault protection of transformer against

A)Heavy loads
B)Internal short circuits
C)External short circuits
D)All of the above

Question 23

In a static over current relay, inverse time characteristics are obtained by

A)A transistor amplifier
B)An integrating circuit
C)A transistor switch
D)A differentiating circuit

Question 24

In the case of transmission line protection, over current relay is used

A)Only up to 110 KV
B)Only up to 220 KV
C)Only up to 50 KV
D)Only up to 1100 KV

Question 25

Directional over current relays have two exciting coils connected across

A)CT secondaries of two different phases
B)VT secondaries of two different phases
C)CT and VT secondaries of same phases
D)CT and VT secondaries of two different phases