Power Systems Switchgear Expected MCQ PDF 3
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Attempt Free Power Systems Switchgear Expected MCQ PDF 3 Here. Read The Important Electrical MCQ From Below.
1) What is switchgear?
a. An apparatus used for switching, controlling and protecting the electrical circuits and equipments.
b. It detects the faults only.
c. It corrects the faults only.
d. All of the above.
ANSWER: All of the above.
2) What is the primary principle of a fuse?
a. Open the circuit.
b. Protect the appliance.
c. Protect the line.
d. Prevent excess current from flowing into the line.
ANSWER: Prevent excess current from flowing into the line.
3) When does the circuit breaker operate in the line?
a. When power is to be supplied.
b. When the line is to be tested.
c. Whenever the fault occurs in the line.
d. Whenever the switch and the relay has to be operated.
ANSWER: Whenever the fault occurs in the line.
Power Systems Switchgear Expected MCQ PDF 3
4) Which device sends the information to the circuit breaker to interrupt the circuit in case of fault?
a. Switch
b. Relay
c. Circuit breaker itself does this function.
d. Fuse.
ANSWER: Relay
5) Which material is used for the manufacture of bus bars?
a. Aluminium rods.
b. Copper rods.
c. Any conducting material.
d. Made of silver.
ANSWER: Copper rods.
6) How is the bus bars rated?
a. Current only.
b. Voltage only.
c. Current, voltage and frequency.
d. Current, voltage, frequency and short circuit current.
ANSWER: Current, voltage, frequency and short circuit current.
Power Systems Switchgear Expected MCQ PDF 3
7) Which among these are the main characteristics of a fuse element?
a. Low melting point
b. High conductivity
c. Least deterioration due to oxidation
d. All of the above
ANSWER: All of the above
8) Which among the following statement is true related to fuse?
a. Greater the current smaller is the time taken by the fuse to blow out.
b. Greater the current greater is the time taken by the fuse to blow out.
c. The current is directly proportion to the blow out time of fuse.
d. Is dependent on the temperature and atmospheric conditions.
ANSWER: Greater the current smaller is the time taken by the fuse to blow out.
Power Systems Switchgear Expected MCQ PDF 3
9) Which among these is the least expensive protection for over current in low voltage system?
a. Rewirable fuse.
b. Isolator.
c. Circuit breaker.
d. Air breaker switch.
ANSWER: Rewirable fuse.
10) For a current upto 10A which material is used as the fusing element?
a. Copper
b. Silver
c. Alloy of lead and tin
d. Zinc
ANSWER: Alloy of lead and tin
Power Systems Switchgear Expected MCQ PDF 3
11) What is the relation between the fusing current and the diameter of the wire?
a. I = k d3
b. I = k d3/2
c. I = k d2
d. I = k d2/3
ANSWER: I = k d3/2
12) What is fusing factor?
a. The ratio of current rating of the fuse to the minimum fusing current
b. The ratio of minimum fusing current to the current rating of the fuse
c. The ratio of maximum fusing current to the current rating of the fuse
d. The ratio of minimum fusing current to the voltage rating of the fuse
ANSWER: The ratio of minimum fusing current to the current rating of the fuse
13) What should be the value of fusing factor?
a. Equal to zero
b. Equal to one
c. Less than one
d. More than one
ANSWER: More than one
Power Systems Switchgear Expected MCQ PDF 3
14) What is the maximum current upto which fuses can be used?
a. 25 A
b. 50 A
c. 75 A
d. 100 A
ANSWER: 100 A
15) What is the typical value of the pre arcing time?
a. 0.1
b. 0.01
c. 0.001
d. 0.0001
ANSWER: 0.001
16) A fuse wire of circular cross section has a radius of 0.8mm. The wire blows off at a current of 9A. What will be the radius of the wire that will blow off
at a current of 1A?
a. 0.2 mm
b. 0.18 mm
c. 0.28 mm
d. 0.3 mm
ANSWER: 0.18 mm
Power Systems Switchgear Expected MCQ PDF 3
17) Which among these tests are performed to check the nation or international standards?
a. Type test.
b. Production tests.
c. Site checks.
d. All of the above.
ANSWER: Type test.
18) If the strands of the fusing wire are twisted, what happens to the fusing current?
a. Increases
b. Reduces.
c. No change/ remains same
d. Depends on the value of current, increases or decreases.
ANSWER: Reduces.
19) What is the cut off current in the fuse?
a. Maximum value actually reached.
b. Rms value actually reached.
c. Average value actually reached.
d. None of the above
ANSWER: Maximum value actually reached.
20) What is the advantage of HRC fuses over Rewirable fuses?
a. High speed operation
b. High rupturing capacity
c. No ageing effect.
d. All of the above.
ANSWER: All of the above.
Power Systems Switchgear Expected MCQ PDF 3
21) Which material is used in the liquid type of fuse?
a. SF6
b. Distilled water
c. Carbon tetra chloride.
d. Mineral oil / transformer oil
ANSWER: Carbon tetra chloride.
22) In a HRC fuse what is the time between the cut off and the final current zero called?
a. Pre – arcing time.
b. Arcing time.
c. Total operating time.
d. None of these.
ANSWER: Arcing time.
23) Upto what voltage a cartridge type of fuse can be used?
a. 400 V
b. 11 kV
c. 20 kV
d. 33 kV
ANSWER: 33 kV
24) On what basis is the selection of fuse done?
a. Steady load.
b. Fluctuating load.
c. Both (a) and (b)
d. None of these.
ANSWER: Both (a) and (b)
Power Systems Switchgear Expected MCQ PDF 3
25) What is the main advantage of using a fuse?
a. Cheapest type of protection.
b. Inverse time current characteristics.
c. Current limiting effect under short circuit conditions.
d. All of above.
ANSWER: All of above.
26) Upto what voltage can the liquid type HRC fuses be used?
a. 33 kV
b. 132 kV
c. 66 kV
d. 220 kV
ANSWER: 132 kV
27) When a fault occurs in a high voltage transmission line, what happens first?
a. Circuit breaker operates then the relay.
b. Relay operates and then the circuit breaker.
c. Relay operates, then successively the isolator and the circuit breaker.
d. Isolator operates, then successively the relay and the circuit breaker.
ANSWER: Relay operates and then the circuit breaker.
28) Which part of the circuit breaker is helpful in breaking the current?
a. Trip coil.
b. Contacts.
c. Medium
d. Handle.
ANSWER: Contacts.
Power Systems Switchgear Expected MCQ PDF 3
29) Which type of tripping is generally preferred for the circuit breaker?
a. Manual
b. Automatically
c. Depending on the voltage level
d. None of the above
ANSWER: Automatically
30) The arc resistance depends on which among the following factors?
a. Cross section of the arc.
b. Length of the arc.
c. Degree of ionization
d. All of the above.
ANSWER: All of the above.
31) How is the initiation of electric arc at the instant of contact separation caused?
a. Thermionic emission of electrons.
b. Field emission of electrons.
c. Both (a) and (b)
d. None of these.
ANSWER: Both (a) and (b)
Power Systems Switchgear Expected MCQ PDF 3
32) Arcing voltage will be the least in case of
a. Carbon
b. Copper
c. Silver
d. Tungsten
ANSWER: Silver
33) What is the arc voltage in a circuit breaker?
a. In phase with the arc current.
b. Lagging the arc current by 90°
c. Leading the arc current by 90°
d. Lagging the arcing current by 180°
ANSWER: In phase with the arc current.
Power Systems Switchgear Expected MCQ PDF 3
34) What happens in the arc extinction using high resistance method?
a. Arc resistance is decreased with time.
b. Arc resistance is increased with time.
c. No change it remains same.
d. Arc resistance is kept zero.
ANSWER: Arc resistance is increased with time.
35) By using low resistance method for arc extension what is the value of arc resistance?
a. Arc resistance is zero.
b. Arc resistance is high
c. Arc resistance is low
d. Arc resistance is very high
ANSWER: Arc resistance is low
Power Systems Switchgear Expected MCQ PDF 3
36) The resistance of an electric arc can be increased by
a. Increasing the concentration of ionised particles.
b. Reducing the arc length.
c. Splitting the arc.
d. Increasing the arc cross section.
ANSWER: Splitting the arc.
37) The heat produced at the contact point owing to flow of electric current is least affected by_________.
a. Temperature of the surrounding medium.
b. Contact resistance.
c. Magnitude of electric current flowing.
d. Duration of flow of current.
ANSWER: Temperature of the surrounding medium.
38) Which of the following should have low value for the contacts and their material?
a. Thermal capacity.
b. Contact resistance.
c. Thermal conductivity.
d. None of above.
ANSWER: Contact resistance.
Power Systems Switchgear Expected MCQ PDF 3
39) In a circuit breaker, ionisation is facilitated by_________________.
a. Increase in field strength.
b. Increase in mean free length.
c. High temperature of the surrounding medium.
d. All of the above.
ANSWER: All of the above.
40) In a circuit breaker the contact space is ionised by what?
a. Field emission from the contact surface.
b. Thermal emission from the contact surface.
c. Thermal ionisation of gas.
d. All of above.
ANSWER: Thermal ionisation of gas.
Power Systems Switchgear Expected MCQ PDF 3
