Question 1

Where severe synchronising swing occur, the relay employed is
A)Impedance relay
B)Mho relay
C)Reactance relay
D)Induction relay

Accepted Answer

Mho relay is preferred for severe synchronizing swings because it is inherently more stable and less affected by power swings compared to other types of relays.

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

Accepted Answer

D

Question 3

For ground fault we prefer
A)Plain impedance relay
B)Directional over current relay
C)Mho relay
D)Reactance relay

Accepted Answer

D

Question 4

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

Accepted Answer

Admittance relay is a type of directional relay. It is used to detect faults in a specific direction in the power system, which is essential for the protection of transmission lines.

Question 5

The relay used for feeder protection is
A)Under voltage relay
B)Translay relay
C)Thermal relay
D)Buchholz relay

Accepted Answer

Translay relay is specifically designed for feeder protection, as it is a type of differential relay that compares the current entering and leaving a section of a power system to detect faults within that section.

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

Accepted Answer

Buchholz relay is specifically designed for detecting and protecting transformers from internal faults. It is used in oil-immersed transformers and operates by detecting the gases that are produced by the electrical faults within the transformer.

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

Accepted Answer

Buchholz relay is specifically designed for oil-filled transformers and can detect incipient faults by sensing the gas accumulation or oil flow within the transformer, thus providing an early warning before a major fault develops.

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

Accepted Answer

Zero sequence current is primarily used in ground over current relays because it is a measure of the unbalanced current in the system, which typically occurs during ground faults.

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

Accepted Answer

Second harmonic currents are used to bias the restraining coil of a differentially connected relay during the energization of a transformer to prevent maloperation. This is because the inrush current, which occurs during transformer energization, contains a high level of second harmonic components, distinguishing it from fault currents.

Question 10

How many relays are used to detect interphase fault of a three line system?
A)One
B)Two
C)Three
D)Six

Accepted Answer

Three relays are used to detect interphase faults in a three-line system, with each relay monitoring for faults between a pair of phases.

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

Accepted Answer

Mho relay is primarily used for protecting up to 90% of the transmission line-length in the forward direction due to its reach and directional sensitivity, making it highly effective for long transmission lines.

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

Accepted Answer

The answer of For protection of parallel feeders fed from...

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

Accepted Answer

Relays can be designed to respond to a variety of changes including resistance, reactance, impedance, voltage, current, and light intensity. This makes them versatile components in various applications, from electrical circuits to automation systems.

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

Accepted Answer

DC shunt relays are made of many turns of thin wire to increase the resistance of the coil and reduce the current flow.

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

Accepted Answer

All the mentioned properties are important to ensure efficient current flow without excessive heating or voltage drop.

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

Accepted Answer

All of the options are necessary for effectively interrupting large currents by a relay: arc suppressing blow out coils help extinguish the arc, wide separation of contacts prevents re-striking, and high-speed opening minimizes the duration of the arc.

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

Accepted Answer

Electronic and bimetallic relays are commonly used to protect electrical equipment handling low power. Electronic relays are versatile and can be designed for various protection schemes, while bimetallic relays offer simple, effective protection based on thermal effects. Thermocouples, although used for temperature measurement, are not typically used as protective relays for electrical equipment.

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

Accepted Answer

The answer of ............. Relays are used for phase faults...

Question 19

........ Relays is preferred for phase fault on short transmission line
A)Induction type
B)Reactance
C)Impedance
D)None of the above

Accepted Answer

Reactance relays are preferred for phase faults on short transmission lines because they are less affected by changes in arc resistance, making them more reliable for this application.

Question 20

The under voltage relay can be used for
A)Generators
B)Bus bars
C)Transformers
D)All of the above

Accepted Answer

Under voltage relays are versatile devices that can be used in various applications to protect electrical equipment from damage caused by low voltage conditions. They are suitable for use with generators, bus bars, and transformers, ensuring these components operate within their designated voltage ranges to prevent malfunction or damage.

Quiz 11: Relaying Schemes and Techniques for Electrical Equipment Protection

Where severe synchronising swing occur, the relay employed is

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

For ground fault we prefer

Admittance relay

The relay used for feeder protection is

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

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

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

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

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

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

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

Relays can be designed to respond to changes in

DC shunt relays are made of

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

Interruption of large currents by relay requires

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

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

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

The under voltage relay can be used for