Insulation Resistance and Capacitance - MCQs with Answers

Insulation Resistance in Underground Cables - MCQs with Answers

Q1. 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

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Q2. 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

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Q3. 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.

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Q4. 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°.

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Q5. 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

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Q6. 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

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