Deck 10: Electrical Protection and Switchgear

Question 1

Large internal faults are protected by

A)Merz price percentage differential protection
B)Mho and ohm relays
C)Horan gaps and temperature relays
D)Earth fault and positive sequence relays

Answer 1

Merz price percentage differential protection

Question 2

Which of the following is the least expensive protection for over current in lowvoltage system ?

A)Rewireable fuse
B)Isolator
C)Oil circuit breaker
D)Air break circuit breaker

Answer 2

Rewireable fuse

Question 3

For the protection of power station buildings against direct strokes the requirements are

A)Interception
B)Interception and conduction
C)Interception, conduction and dissipation
D)Interception,conduction,dissipation and reflection

Answer 3

Interception, conduction and dissipation

Question 4

The line insulation is............. the insulation level at the station equipment

A)Less than
B)Same as
C)More than
D)Not directly related with

Question 5

Short-circuit currents are due to

A)Single phase to ground faults
B)Phase to phase faults
C)Three phase faults
D)Any of these

Question 6

For which of the following protection from negative sequence current is provided?

A)Generators
B)Motors
C)Transmission line
D)Transformers

Question 7

For which of the following ratings of the transformer differential protection is recommended?

A)Above 30 KVA
B)Equal to and above 5 MVA
C)Equal two and above 25 MVA
D)None of the above

Question 8

Over voltage protection is recommended for

A)Hydro electric generators
B)Steam turbine generators
C)Gasturbine generators
D)All of the above

Question 9

Overfluxing protection is recommended for

A)Distribution transformer
B)Generator transformer of the power plant
C)Auto transformer of the power plant
D)Station transformer of the power plant

Question 10

Hey switchgear is device used for

A)Interrupting an electrical circuit
B)Switching an electrical circuit
C)Reaching and controlling an electrical circuit
D)Switching, controlling and protecting the electrical circuit and equipment

Question 11

Switching over voltage arc are more hazardous than lighting surges in case of

A)Unbalanced systems
B)Low-voltages
C)11 KV systems
D)EHV and UHV systems

Question 12

Least number of faults are generally reported for

A)Transmission lines
B)Cables
C)Switchgears
D)Transformers

Question 13

Minimum working voltage will be least in case of

A)Silver
B)Graphite
C)Carbon
D)Tungsten

Question 14

In a contactor, interrupting medium may be

A)Air
B)Oil
C)Sf6 gas
D)Any of the above

Question 15

The transient voltages that appears across the contacts at the instant of arc extinction is called ..............voltage

A)Supply
B)Recovery
C)Restriking
D)Peak

Question 16

The power loss is an important factor for the design of

A)Transmission line
B)Motor
C)Generator
D)Feeder

Question 17

SF6 gas

A)Is yellow in colour
B)Is lighter than air
C)Is non-toxic
D)Has pungent small

Question 18

SF6 gas is transported in

A)Air cylinders
B)Gas cylinders
C)Liquid from in cylinders
D)Solid form in boxes

Question 19

The short-circuit in any winding of the transformer is the result of

A)Mechanical vibration
B)Insulation failure
C)Loose connection
D)Impulse voltage

Question 20

The actuating quantity for the relays may be

A)Magnitude
B)Frequency
C)Phase angle
D)Any of the above

Question 21

The operating speed of a relay depends upon the

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

Question 22

Inverse time current relays are used for the protection of

A)Feeders
B)Transformers
C)Alternators
D)Both A and B

Question 23

IDMT relays are used to protect the power transformers against

A)External short-circuit
B)Over loads
C)Internal short-circuits
D)Both A and B

Question 24

In distance protection, the relay measures

A)Negative sequence impedance of the light from relay up to the fault point
B)Positive sequence impedance of the line from relay up to the fault point
C)Self impedance of the line from relay up to the fault point
D)Zero sequence impedance of the line from relay up to the fault point

Question 25

The relay used for phase fault protection of short transmission lines is

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