Power Systems Assessment Questions 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
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 _________
3. Distributors fed at both ends has an advantage of ________________
A. continuous supply
B. fault isolation
C. being economical
D. all of the mentioned
Answer: D
Clarification: 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?
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
Answer: A
Clarification: 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 ___________
Answer: D
Clarification: 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 _____________
7. The distribution feeding system of ring main system has ______________
A. one feeder
B. 2 feeders
C. 4 feeders
D. cannot be said
Answer: A
Clarification: 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
Answer: A
Clarification: 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
Answer: A
Clarification: 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
Answer: A
Clarification: Because of the armouring of the cables leads to eddy current in the power cables adding more to the losses.