Power Systems Questions and Answers – Flux Linkages of an Isolated Current-Carrying Conductor

This set of Power Systems Multiple Choice Questions & Answers (MCQs) focuses on “Flux Linkages of an Isolated Current-Carrying Conductor”.

1. A 500 MW, 21 kV, 50 Hz three phase two pole alternator has 0.8 lagging p.f. with moment of inertia of 27.5×103 kgm-2. The inertia constant H will be _______ MJ/MVA.
a) 2.17
b) 4.2
c) 2.82
d) 2.62
View Answer

Answer: a
Explanation:
The inertia constant H will be 2.17 MJ/MVA for 500 MW, 21 kV, 50 Hz three phase two pole

2. If the power system network is at Vs∠δ and receiving end voltage is Vr∠0 consisting of the impedance of TL as (R+j5)Ω. For maximum power transfer to the load, the most appropriate value of resistance R should be __________
a) 1.732
b) 3
c) 1.2
d) 0.33
View Answer

Answer: a
Explanation: For maximum power transfer, X=√3 R
3=√3 R
R=√3.

3. At a 33kV 50 Hz to a bus a load of 35 MW is connected. To improve the power factor to unity a synchronous phase modifier is connected taking 5 MW. If the SPM is represented as delta connected impedance, where in each phase we have capacitor connected parallel to resistance forming RC parallel network, then the value of this resistance is ___________
a) 653.4 Ω
b) 753.6 Ω
c) 280.4 Ω
d) 682 Ω
View Answer

Answer: a
Explanation: Reactive power fed by SPM = 35tan36.87 = 26.25 MVAR
Active power consumed by prime mover = 5 MW
5*106 = 3V2/R
R=3(33×1000)2/(5*106) = 653.4 Ω.
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4. At a 33kV 50 Hz to a bus a load of 35 MW is connected. To improve the power factor to unity a synchronous phase modifier is connected taking 5 MW. If the SPM is represented as delta connected impedance, where in each phase we have capacitor connected parallel to resistance forming RC parallel network, then the value of this capacitance is __________
a) 25.57 μF
b) 76.2 μF
c) 32.2 μF
d) 24 μF
View Answer

Answer: a
Explanation: Q=3V2Cω
C= 25.57 μF.

5. The transmission efficiency for a single phase line can be expressed as ____________
a) \(\frac{VrI \cos \theta}{Vr \cos \theta r + 2RI^2}\)
b) \(\frac{VrI \cos \theta}{Vr \cos \theta r + RI^2}\)
c) \(\frac{VrI \cos \theta}{Vr \cos \theta r + 3RI^2}\)
d) \(\frac{\sqrt{3} VrI \cos \theta}{\sqrt{3} Vr \cos \theta r + 2RI^2}\)
View Answer

Answer: a
Explanation: The efficiency of single phase is
\(\frac{VrI \cos \theta}{Vr \cos \theta r + 2RI^2}\)
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6. The transmission efficiency for a three phase line can be expressed as _________
a) \(\frac{\sqrt{3} VrI \cos \theta}{\sqrt{3} Vr \cos \theta r + 2RI^2}\)
b) \(\frac{\sqrt{3} VrI \cos \theta}{\sqrt{3} Vr \cos \theta r + 3RI^2}\)
c) \(\frac{3 VrI \cos \theta}{3 Vr \cos \theta r + 2RI^2}\)
d) \(\frac{3 VrI \cos \theta}{3 Vr \cos \theta r + 3RI^2}\)
View Answer

Answer: a
Explanation: The efficiency of three phase system is
\(\frac{\sqrt{3} VrI \cos \theta}{\sqrt{3} Vr \cos \theta r + 2RI^2}\)

7. If the flux linkages are varied sinusoid with current, then what can be concluded about the inductance?
a) Constant
b) Varying with the current
c) Linearly varying
d) Exponential change
View Answer

Answer: b
Explanation: Inductance = flux linkages/current.

8. The principle behind the influence of the power lines on the telephone lines is __________
a) Faraday’s laws
b) Mutual inductance
c) Self inductance
d) All of the mentioned
View Answer

Answer: a
Explanation: The concept of mutual inductance is the main reason for the interference between telephone lines and the power lines.

9. The magnetic flux intensity due to the current flowing inside the conductor is _________
Find the magnetic flux intensity due to the current flowing inside the conductor
a) \(\frac{yI}{2 \pi r^2}\)
b) \(\frac{yI}{\pi r^2}\)
c) \(\frac{rI}{2 \pi y^2}\)
d) \(\frac{rI}{2 \pi y^2}\)
View Answer

Answer: a
Explanation: Referring the ampere’s Law,
2Ï€yH=Iy
Assuming uniform current density,
The magnetic flux intensity due to the current flowing inside the conductor is yI/ 2r2
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10. The flux density B, y meters from the centre of conductors in the following diagram, is _______
a) \(\frac{\mu y I}{2 \pi r^2}\)
b) \(\frac{y I}{2 \pi r^2 \mu}\)
c) \(\frac{5 \mu y I}{2 \pi r^2}\)
d) \(\frac{\mu r I}{2 \pi y^2}\)
View Answer

Answer: a
Explanation: Referring the ampere’s Law,
2Ï€yH=Iy
Assuming uniform current density,
The flux density B y meters from centre of conductors in the following diagram is 2Ï€yH=Iy

11.The internal flux linking the single infinite conductor causes the inductance of ___________
a) 0.5 *10-7 H/m
b) 2 *10-7 H/m
c) 0.5 *10-7 ln(r) H/m
d) 2 *10-6 H/m
View Answer

Answer: a
Explanation: λint = I/2 x 10-7 Wb-T/m
L= λint/I = 0.5 *10-7 H/m.

12. The inductance of the conductor contributed by the flux between the point D outside at the distance d from conductor is _____________
a) 0.461 log(d/r) mH/km
b) 0.4 log(d/r) mH/km
c) 0.461 log(r/d) mH/km
d) 0.461 log(d/r) H/km
View Answer

Answer: a
Explanation: L= 0.461 log(d/r) mH/km.

Sanfoundry Global Education & Learning Series – Power Systems.

To practice all areas of Power Systems, here is complete set of 1000+ Multiple Choice Questions and Answers.

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