This set of Power Systems Multiple Choice Questions & Answers (MCQs) 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
Explanation: Copper losses for a three-phase four wire system will be,
\(\frac{2}{3} \cdot \frac{P^2}{V^2 \cdot \cos^2 \theta} \cdot R = \frac{2}{3} \cdot \frac{120000^2}{415^2 \cdot (0.75)^2} \cdot 0.05\) = 4955 W.
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 _________
a) \(\frac{4}{3 \cos Ø^2}\)
b) \(\frac{3}{4 \cos Ø^2}\)
c) \(\frac{1}{3 \cos Ø^2}\)
d) \(\frac{1}{\cos Ø^2}\)
View Answer
Explanation: The ratio of area of cross section of the conductor used in 3-ph 3-wire to dc 2-wire will be \(\frac{4}{3 \cos Ø^2}\) 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
Explanation: All the points mentioned are the benefits of the dual fed distribution system.
4. Why is a ring main distribution system preferred to a radial system?
i. Voltage drop in feed is more
ii. Supply is reliable
iii. Power factor is higher
a) ii
b) i,ii
c) i,ii,iii
d) ii,iii
View Answer
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 ___________
a) \(\frac{1}{x^2}a\)
b) \(\frac{1}{x}a\)
c) x2a
d) none of the mentioned
View Answer
Explanation: The cross-sectional area has to be increased not reduced after reducing the voltage levels.
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 _____________
a) \(\frac{1}{x^2}a\)
b) \(\frac{1}{x}a\)
c) x2a
d) none of the mentioned
View Answer
Explanation: Assuming 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
Explanation: Ring main uses only one feeder.
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
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
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.
10. Single core cables for an ac systems are not provided with armouring.
a) True
b) False
View Answer
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.
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