# Power Systems Questions and Answers – Parallel Circuit Three Phase Lines

This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Parallel Circuit Three Phase Lines”.

1. Nominal-T and nominal-π are equivalent to each other.
a) True
b) False

Explanation: Nominal-T and nominal-π are not equivalent to each other. They can’t be interchanged.

2. For the circuit representation of a transmission line below, the transmission line T-matrix will be ___________

Explanation: Applying KVL and KCL,
Vs = Vr
Is = Y * Vs + Ir.

3. For the circuit representation of a transmission line below, the transmission line T-matrix will be . Then AB – CD value will be _________

a) Y
b) 1
c) -Y
d) 1-Y

Explanation: Applying KVL and KCL,
Vs = Vr
Is = Y * Vs + Ir
AB-CD = 0-Y = -Y.

4. The transfer of the reactive power over a line mainly depends upon _____
a) Vr
b) Vs
c) |Vs| – |Vr|
d) Power angle

Explanation: Reactive power flow depends on the |Vs|-|Vr|.

5. For a medium transmission line system if the sending end line voltage is 143 kV with the line impedance as 101.24∠74° Ω and shunt admittance of 7.38*10-4∠90° Ω-1.Then the no load line voltage at the receiving end would be _________
a) 148.3 kV
b) 140.8 kV
c) 149.2 kV
d) 132 kV

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6. For a medium transmission line system if the sending end line voltage is 143 kV with the line impedance as 101.24∠74° Ω and shunt admittance of 7.38*10-4∠90° Ω-1 delivering 25 MVA at 0.8 power factor lagging in nature to the load at 132 kV. The voltage regulation is ___________
a) 12.3
b) 12.8
c) 14.2
d) -2.3

Voltage regulation = (148.3-132)/132 = 12.3%.

7. For the lines more than 250 km, the parameters of a line are considered not ______ but _____
a) lumped, distributed
b) distributed, lumped
c) lumped, non uniform lumped
d) uniform, lumped

Explanation: For long transmission lines, the parameters are considered uniformly distributed.

8. Which of the parameters of a long transmission line and medium transmission lines are same?
a) A and D
b) B, C
c) Only A
d) Only D

Explanation: A and D parameters of LTL and MTL are almost same.

9. With 100% series compensation of the transmission lines, which of the following effects are observed?
(i) Low transient voltage
(ii) High transient current
(iii) The current is series resonant at power frequency
a) (ii), (iii)
b) (i), (ii)
c) (i), (ii), (iii)
d) (iii)

Explanation: 100% compensation of the line results in high transient current at power frequency.

10. With 100% series compensation of the transmission lines, which of the following effects are not observed?
(i) Low transient voltage
(ii) High transient current
(iii) The current is series resonant at power frequency
a) (ii), (iii)
b) (i)
c) (i), (ii), (iii)
d) (iii)

Explanation: 100% compensation of the line results in high transient current at power frequency.

11. Estimate the transmission line parameters (ABCD), for the given distributed network.

Explanation: Vs= Z1*Is + Y-1*(Is+Ir)
Vr = Z2*Ir + Y-1*(Is+Ir)
VY = Is+Ir
Solving above equation, we get

12. Estimate the transmission line parameters (ABCD), for the given distributed network and find AB-CD.

a) 1
b) Y
c) Y-Z1Z2
d) 0

Explanation: Vs= Z1*Is + Y-1*(Is+Ir)
Vr = Z2*Ir + Y-1*(Is+Ir)
VY = Is+Ir
Solving above eq, we get

13. Estimate the transmission line parameters (ABCD), for the given distributed network.

Explanation: Applying KVL in the middle loop and KCL at the two nodes, we will get

14. Surge impedance for 400ohms implies for a transmission line that ___________
a) line can be theoretically loaded up to 400ohms
b) line can be practically loaded up to 400ohms
c) open circuit impedance of 400ohms
d) short circuit impedance of 400ohms

Explanation: Surge impedance decides the maximum value for a transmission line loading.

Sanfoundry Global Education & Learning Series – Power Systems.

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