# Power Systems Questions and Answers – Effect of Earth on the Three Phase Transmission Line Capacitance – 1

This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Effect of Earth on the Three Phase Transmission Line Capacitance – 1”.

1. Transmission efficiency of a transmission line increases with the _____________
a) decrease in power factor and voltage
b) increase in power factor and voltage
c) increase in power factor but the decrease in voltage
d) increase in voltage only power factor remains constant

Explanation: Increasing the power factor and voltage reduces the losses and hence improves the efficiency.

2. Surge impedance of a transmission line is the impedance at the time of breakdown of voltage.
a) True
b) False

Explanation: Surge impedance is the characteristic impedance of a TL.

3. When the transmission line is lousy, then its characteristic impedance will not depend on which of the following?
a) Length
b) Operating frequency
c) Sub synchronous frequency
d) Length and Sub synchronous frequency

Explanation: For a lousy line, the characteristic impedance will be independent of its sub synchronous frequency and length.

4. If the transmission line is lossless, then its characteristic will be _________
a) √(L/C)
b) √LC
c) √(L+C)
d) √(C/L)

Explanation: The characteristic impedance for the lossless lines is given by √(L/C) because the resistance is zero.

5. The surge impedance of multiple conductor lines as compared to single line is _______
a) higher
b) lower
c) same
d) length dependent

Explanation: Due to the reduced GMD, the impedance decreases and so the surge impedance.

6. When ______ then the transmission line will act as a distortion less line.
a) RC = GL
b) RG = LC
c) R = G
d) Cannot be determined

Explanation: When both the time constants become same, then the transmission will behave like distortion less line.

7. It is intended to increase the power despatch of the existing transmission line. Then what can be the most appropriate solution for improving it?
a) Installing series capacitors
b) Installing shunt capacitor
c) Installing shunt reactor
d) Installing series reactor

Explanation: Series capacitors reduce the power as

8. Which of the following situations is very useless when the series capacitors to the transmission line are of little use?
a) When the VAR requirement is small
b) When the VAR requirement is large
c) When the VAR requirement is varying
d) Cannot be determined

Explanation: Because capacitance is usually neglected for a small transmission line.

9. Reactive power requirement of a power transmission system depends on __
a) Power angle δ
b) |Vs|-|Vr|
c) Vs
d) Vr

10. When do we use conduit pipe in the transmission of power?
a) Unsheathed cables
b) Armoured cables
c) PVC sheathed cables
d) All of the mentioned

Explanation: It is used in protection of wires and cables for underground transmission.

Sanfoundry Global Education & Learning Series – Power Systems.

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