# Power Systems Questions and Answers – Short Transmission Line – 2

This set of Power Systems Multiple Choice Questions & Answers focuses on “Short Transmission Line – 2”.

1. What is the value of charging current in short transmission lines?
a) Less than medium transmission lines
b) Equal to medium transmission lines
c) More than medium transmission lines
d) More than long transmission lines

Explanation: Line to Earth capacitance of short transmission line is less than that in medium and long transmission line and is negligable. Because of this the charging current of short transmission line is less than that in medium and long transmission line and is negligable.

2. What is the value of Inductive reactance in short transmission lines?
a) More at reciving end
b) More at sending end
c) Uniformly distributed over entire length
d) More in middle of sending end and reciving end

Explanation: Actually the inductive reactance of line is uniformly distributed over its entire length. To make calculations simple this reactance is assumed to be lumped and connected in series with the line.

3. Regulation of short transmission lines depends:
a) Only on line resistance
b) Only on line inductance
c) Only on line capacitance
d) On line inductance and line resistance

Explanation: The expression of voltage regulation of short transmission line shows that, its voltage regulation depends on line resistance and line inductive reactance. Capacitance of short transmission line is negligible so it does not cause its effecting it.

4. What is the percentage voltage regulation of short transmission line if its sending end and reciving end voltages are 160 KV and 132 KV respectively?
a) 30 %
b) 21.21 %
c) 12.12 %
d) 38.22 %

Explanation: % Voltage Regulation = (Sending end voltage -Reciving end voltage) ÷ Reciving end voltage
= [( 160 – 132 ) × 100] ÷ 132
= 21.21 %.

5. A single phase transmission line is transmitting 1,100 KW power at 11 KV and at unity power fector. If it has a total resistance of 5 Ω, what is the efficiency of the transmission line?
a) 80 %
b) 89.65 %
c) 97.24 %
d) 99.54 %

Explanation: Efficiency (η) = Power delivered ÷ (Power Delivered + line losses)
Line current (I) = P/V
= (1100 × 1000/11000)
= 100 Amp.
Line losses = I2 R
= (100)2 5
= 50 KW
η = [11000/(11000+50)] × 100
= 99.54 %.

6. Voltage regulation of a transmission line should be ________
a) Minimum
b) Maximum
c) Greater than 50 %
d) Less than 50 %

Explanation: More value of voltage regulation means more voltage fluctuations and this is undesirable. So the value of voltage regulation should be as low as possible.

7. Which of the following is like equivalent circuit of short transmission line?
a) Series RLC circuit
b) Parallel RLC circuit
c) Series RL circuit
d) Parallel RL circuit

Explanation: Due to smaller distance and lower line voltage, the shunt capacitance effects are extremely small and also the shunt conductance effects are very low. So both of them are neglected and equivalent circuit contains only series inductance(L) and resistance(R).

8. In single phase transmission lines resistance and inductance are considered only up to neutral.
a) True
b) False

Explanation: In case of single phase transmission lines the total loop resistance and inductance is to be taken into account. Resistance and inductance only up to neutral are taken into account for 3 phase transmission lines.

Sanfoundry Global Education & Learning Series – Power Systems. 