POWER SYSTEMS MCQS SET 03

POWER SYSTEMS MCQS SET 03

Transmission & Distribution of Electrical Power 

1. Why solid type of conductors is not preferred for the voltages exceeding 66 kV?
a. A danger of breakdown of insulation.
b. Skin effect dominates the conductor.
c. There is corona loss between conductor and sheath material.
d. Insulation melts due to overheating.
ANSWER: a. A danger of breakdown of insulation.
 

2. A single core cable has a conductor diameter of 1 cm and the insulation thickness of 0.4 cm. If the specific resistance of insulation is 5.5 * 1014 Ω -cm, what will be the insulation resistance for a length of 3 km?
a. 0.234 * 109 Ω         b. 0.257 * 109 Ω        c. 0.352 * 109 Ω
d. 0.211 * 109 Ω
ANSWER: b. 0.257 * 109 Ω
 

3. A single core cable 5 km long has an insulation resistance of 0.35 M Ω. The core diameter is 20 mm and the diameter of the cable over the insulation is 50mm. What will be the resistivity of the insulating material?
a. 13 * 109 Ω m                 b. 12 * 109 Ω m
c. 13.5 * 109 Ω m              d. 12.85 * 109 Ω m
ANSWER: b. 12 * 109 Ω m
 

4. On which factor does the capacitance of the cable depend upon?
a. Length of cable.
b. Relative permittivity of dielectric used in cable.
c. Ratio of sheath diameter and core diameter.
d. All of the above.
ANSWER: d. All of the above.
 

5. The charging current drawn by the cable _______.
a. Lags behind the voltage by 90°.
b. Leads the voltage by 90°.
c. Are in phase with each other.
d. Leads the voltage by 60°.
ANSWER: Leads the voltage by 90°.
 

6. A single core cable has a conductor diameter of 1 cm and the internal sheath diameter of 1.8 cm. If impregnated paper of relative permittivity 4 is used as the insulation, calculate the capacitance for 1 km length of cable?
a. 0.378 μ F      b. 0.264 μ F    c. 0.549 μ F    d. 0.78 μ F
ANSWER: a. 0.378 µ F
 

7. What is the total charging current per phase for a 33 kV, 50 Hz, 3 phase underground cable of 4 km length using 3 single core cables? Each conductor has a diameter of 2.5 cm and the radial thickness of insulation is 0.5 cm
a. 15.28 A        b. 11.87 A         c. 13.85 A        d. 8.25 A
ANSWER: b. 11.87 A
 

8. What is the maximum stress in the insulation for a 33 kV single core cable with a diameter of 1 cm and a sheath of inside diameter 4 cm?
a. 50.61 kV / cm rms            b. 45.231 kV / cm rms
c. 47.61 kV / cm rms           d. 49.231 kV /cm rms
ANSWER: c. 47.61 kV / cm rms
 

9. What will be the insulation thickness for a conductor of diameter 2 cm, with maximum and minimum stress 40 kV / cm rms and 10 kV / cm rms respectively?
a. 5 cm        b. 3 cm        c. 2 cm         d. 4 cm
ANSWER: b. 3 cm
 

10. What will be the most economical value of diameter of a single core cable to be used on 50 kV, single phase system, when the maximum permissible stress is not exceeding 50 kV / cm?
a. 2.52 cm         b. 2.828 cm         c. 3.52 cm        d. 3.82 cm
ANSWER: b. 2.828 cm