Deck 5: Electrical Protection and Switchgear Systems

Question 1

Oil switches are employed for

A)low currents circuits
B)low voltages circuits
C)high voltages and large currents circuits
D)all circuits

Answer 1

high voltages and large currents circuits

Question 2

A switchgear is device used for

A)interrupting an electrical circuit
B)switching an electrical circuit 111.
C)switching and controlling an electrical circuit
D)switching, controlling and protecting the electrical circuit and equipment

Answer 2

switching, controlling and protecting the electrical circuit and equipment

Question 3

The fuse wire, in D.C. circuits, is inserted in

A)negative circuit only
B)positive circuit only
C)both (a) and (b)
D)either (a) or (b)

Answer 3

both (a) and (b)

Question 4

By which of the following methods major portion of the heat generated in a H.R.C. fuse is dissipated ?

A)Radiation
B)Convection
C)Conduction
D)All of the above

Question 5

A short-circuit is identified by

A)no current flow
B)heavy current flow
C)voltage drop
D)voltage rise

Question 6

The information to the circuit breaker under fault conditions is provided by

A)relay
B)rewirable fuse
C)H.R.C. only
D)all of the above

Question 7

To limit short-circuit current in a power system are used.

A)earth wires
B)isolators
C)H.R.C. fuses
D)reactors

Question 8

A balanced 3-phase system consists of

A)zero sequence currents only
B)positive sequence currents only
C)negative and zero sequence currents
D)zero, negative and positive sequence currents

Question 9

In a single bus-bar system there will be complete shut down when

A)fault occurs on the bus itself
B)fault occurs on neutral line
C)two or more faults occur simultaneously
D)fault occurs with respect to earthing

Question 10

Which device is used for protection of equipment from from damage caused by overload or short circuit?

A)CVT
B)Circuit Breaker
C)Current Transformer
D)Lighting Arrester

Question 11

Isolator in substation is open under ------------- condition?

A)No load
B)Short Circuit
C)Full Load
D)Any of the above

Question 12

Earthling switch is used for

A)measuring of safety voltage
B)protection of equipment from ground faults
C)discharging residual energies
D)all of the above

Question 13

If the time of operating of a relay for unity TMS is 10secs., the time of operation for 0.5 TMS will be

A)20 secs.
B)5 secs.
C)10 secs.
D)None of the above

Question 14

A fault is more severe from the view point of RRRV if is a

A)Short line fault.
B)Medium length line fault.
C)Long line fault.
D)None of these.

Question 15

A reactance relay is

A)Voltage restrained directional relay.
B)Directional restrained over-current relay.
C)Voltage restrained over-current relay.
D)None of the above.

Question 16

For measuring positive, negative and zero sequence voltages in a system, the reference is taken as

A)Neutral of the system only.
B)Ground only.
C)For zero sequence neutral and for positive and negative the ground.
D)None of the above.

Question 17

Positive, negative and zero sequence impedances of a solidly grounded system under steady state condition always follow the relations

A)Z4>Z2>Z0
B)Z2>Z4>Z0
C)Z0>Z4>Z2
D)None of the above

Question 18

Phase comparators in case of static relays and electro-mechanical relays normally are

A)Sine and cosine comparators respectively
B)Cosine and sine comparators respectively.
C)Both are cosine comparators.
D)Both are sing comparators.

Question 19

For reducing tower footing resistance it is better to use

A)Chemical and ground rods only.
B)Chemical and counterpoise only.
C)Ground rod and counterpoise only.
D)Chemical, ground rods and counterpoise.

Question 20

Rate of rise of restriking voltage depends

A)Type of circuit breaker.
B)Inductance of the system only.
C)Capacitance of the system only.
D)Inductance and capacitance of the system

Question 21

What is the purpose of back up protection?

A)To increase the speed
B)To increase the reach
C)To leave no blind spot
D)To guard against failure of primary

Question 22

What is the actuating quantity for the relays?

A)Magnitude
B)Frequency
C)Phase angle
D)All of these

Question 23

Protective relays can be designed to respond to

A)Light intensity, impedance
B)Temperature, resistance, reactance
C)Voltage and current
D)All of these

Question 24

On what factor does the operating speed of the relay depend upon?

A)Rate of flux built up
B)Armature core air gap
C)spring tension
D)All of these

Question 25

What does the third part consist of?

A)Primary winding of a current CT which is connected in series with the line to be protected.
B)Secondary of the CT and the operating coil.
C)Tripping circuit.
D)All of these.