Power Systems Questions and Answers – Distribution Systems – 3

This set of Power Systems Assessment Questions and Answers focuses on “Distribution Systems – 3”.

1. For an ac three-phase four wire system, having a voltage of 415V, with load of 120 kW and resistance of 0.05Ω at power factor of 0.75. The incurred copper losses of the system is ____
a) 4.955 kW
b) 47 kW
c) 49 kW
d) 7.9 kW
View Answer

Answer: a
Explanation: Copper losses for a three-phase four wire system will be,
The incurred copper losses is 4.955 kW with load of 120 kW & resistance of 0.05Ω

2. The ratio of area of cross section of the wire of a 3-phase 3-wire and that of dc 2-wire mid point earthed system will be _________
Find ratio of area of wire of 3-phase 3-wire & dc 2-wire mid point earthed system
View Answer

Answer: a
Explanation: The ratio of area of cross section of the conductor used in 3-ph 3-wire to dc 2-wire will be The ratio of area of cross section of the conductor used in 3-ph 3-wire to dc 2-wire as the power factor will come into picture.

3. Distributors fed at both ends has an advantage of ________________
a) continuous supply
b) fault isolation
c) being economical
d) all of the mentioned
View Answer

Answer: d
Explanation: All the points mentioned are the benefits of the dual fed distribution system.
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4. Why is a ring main distribution system preferred to a radial system?
1. Voltage drop in feed is more
2. Supply is reliable
3. Power factor is higher
a) 2
b) 1,2
c) 1,2,3
d) 2,3
View Answer

Answer: a
Explanation: Ring main system has less voltage drop and power factor at the consumer level is not high.

5. For a given power delivered, if the working voltage of a distribution line is decreased to ‘x’ times, the cross sectional area ‘a’ of distributor line would reduce to ___________
Find cross sectional area ‘a’ of distributor line of line is decreased to ‘x’ times
View Answer

Answer: d
Explanation: The cross-sectional area has to be increased not reduced after reducing the voltage levels.
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6. For a given power delivered, if the working voltage of a distribution line is increased to ‘x’ times, the cross sectional area ‘a’ of distributor line would reduce to _____________
Find cross sectional area ‘a’ of distributor line of line is increased to ‘x’ times
View Answer

Answer: a
Explanation: Assuming the power at both the times remain constant.
The power at both the times remain constant

7. The distribution feeding system of ring main system has ______________
a) one feeder
b) 2 feeders
c) 4 feeders
d) cannot be said
View Answer

Answer: a
Explanation: Ring main uses only one feeder.
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8. A substation records a dip in the voltage received by 15%. To overcome this issue, the booster employed at the substation is ___________
a) a series wound generator coupled to dc shunt motor
b) a series wound motor
c) a shunt motor operating at lagging power factor
d) a shunt motor coupled to differential motor
View Answer

Answer: a
Explanation: A dc series motor coupled with the shunt motor has the ability to boost the voltage at its input supply.

9. A substation records a dip in the voltage received by 15%. To overcome this issue, the booster employed at the substation which should have a _____________
a) low voltage and high current generator
b) high voltage and low current generator
c) medium voltage but high current generator
d) any of the mentioned
View Answer

Answer: a
Explanation: The booster need to have the low voltage and high current profile so that it can easily boost the voltage levels at its output.
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10. Single core cables for an ac systems are not provided with armouring.
a) True
b) False
View Answer

Answer: a
Explanation: Because of the armouring of the cables leads to eddy current in the power cables adding more to the losses.

Sanfoundry Global Education & Learning Series – Power Systems.

To practice all areas of Power Systems Assessment Questions, here is complete set of 1000+ Multiple Choice Questions and Answers.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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