# Power Systems Questions and Answers – Capacitance of a Three-phase Line

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This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Capacitance of a Three-phase Line”.

1. For a transmission line of length not more than 80 km, then it is convenient to lump the capacitance at ________
a) receiving end
b) sending end
c) midpoint
d) anywhere long the line

Explanation: The capacitance should be best lumped at the receiving end for the simpler calculations.

2. At the no load conditions, the current is detected in the transmission line. This can be attributed due to __________
a) capacitance effect
b) proximity effect
c) corona effect
d) back flow through earth

Explanation: At the no load current the shunt connected capacitance allows the flow of the current through the circuit.

3. Identify the characteristics of the Ferranti effect.
(i) Flow of unduly heavy current
(ii) It occurs at unloaded condition
(iii) Rise in the receiving end voltage

Explanation: Ferranti effect occurs at no load condition and it causes rise in voltage.
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4. Ferranti effect is very prominent in occurrence in what type of transmission line?

Explanation: Ferranti effect occurs more in long TL and especially when they are not loaded.

5. The transmission line parameters ABCD for a three phase transposed line with passive and linear elements are ____________
a) always equal
b) never same
c) A and D are same
d) B and C are same

Explanation: The A and D parameter will only be constant.

6. For a general transmission system, the calculated parameter A for a medium transmission line has magnitude _____________
a) close to but less than 1
b) close to but more than 1
c) average of B and C parameter
d) none of the mentioned

Explanation: |A| < 1 but less than 1.

7. The impedance known as surge impedance and characteristic impedance are same.
a) True
b) False

Explanation: Both the impedances are same.

8. Characteristic impedance of a transmission line depends upon ____________
a) geometrical configurations of conductor
b) shape of conductor
c) conductivity
d) surrounding of the conductor.

Explanation: Characteristic impedance of a transmission line will depend on conductor configuration.

9. What will happen when the characteristic impedance of a transmission line is equal t the load impedance ______________
a) all the given energy will be absorbed by the load
b) all the given energy will be transferred to load
c) system will undergo resonance
d) all the given energy will be lost in transmission losses.

Explanation: When the characteristic impedance will be same as load then the load will absorb all the energy.

10. The transmission capacity of a line at 50 Hz frequency as compared to that at 60 Hz is ______
a) higher
b) lower
c) same
d) can’t be decided

Explanation: Due to drop in frequency the losses will reduce.

11. Use of additional shunt capacitor can be made for increasing the capability of the line as it will ______
a) reduce surge impedance
b) increase phase shift
c) increase the angle α
d) all of the mentioned

Explanation: Due to addition of capacitance, the impedance will reduce and power capability will increase.

12. To increase the transmission capability of a high voltage long line ____________
a) series reactance can be reduced
b) resistance can be increased
c) resistance can be decreased
d) shunt admittance can be reduced

Explanation: Transmission capability is inversely proportional to the reactance.

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