Distribution Systems, Cables & Insulators

Power System MCQs

1. The insulation resistance of a cable of 10 km length is 1 MΩ. The resistance for a length of 40 km is______.

a. Can't be determined

b. 0.25 MΩ

c. 4 MΩ

d. 1 MΩ

2. Sheath losses can be eliminated by________.

a. Cross bonding

b. Transposing cable along with cross bonding

c. Transposing cables only

d. None are effective

3. Armouring protect cables against_______.

a. Stray magnetic fields

b. Mechanical damage

c. Capacitance leakage

d. Earth fault

4. Which of the following distribution systems is the most economical?

a. Three phase, 3-wire AC system

b. Three phase, 4-wire AC system

c. DC system

d. Single phase AC system

5. For high voltage transmission lines, conductors are suspended from towers so as to_____.

a. Reduce clearance from ground

b. Take care of increase in length

c. Reduce wind and snow effect

d. Increase clearance from ground

6. The function of steel wire in an ACSR conductor is to______.

a. Reduce inductance

b. Provide additional mechanical strength

c. Take care of surges

d. Compensate for skin effect

7. The string efficiency of insulators can be increased by_______.

a. Changing orientation of strings

b. Correct grading of insulators of various capacitances

c. Increasing the number of strings

d. Reducing the number of strings

8. The insulating materials most commonly used in a cable is_______.

a. VIR

b. PVC

c. Impregnated paper

d. All of the above

9. If the frequency of a transmission system is changed from 50 Hz to 1000Hz, the string efficiency will_______.

a. May increase or decease

b. Remains unchanged

c. Decrease

d. Increase

10. The insulation thickness on the conductor in cables depends upon________.

a. Current

b. Reactive power

c. Power factor

d. Voltage

11. Which of the following distribution system is the simplest and have lowest installation cost?

a. Ring main system

b. Radial system

c. Inter connected system

d. None of the above

12. The dielectric loss in a cable is not a function of________.

a. Radius of the conductor

b. Square of the voltage

c. Frequency of supply

d. Capacitance of the cable

13. Which of the following is not a characteristic of a ring main distributor?

a. Greater reliability

b. More power loss

c. Greater voltage regulation

d. Better flexibility

14. For an existing AC transmission line, the string efficiency is 80%, if DC voltage is supplied for the same set up, the string efficiency will be_______.

a. 100%

b. 90%

c. 80%

d. < 80%

15. In a three unit insulator string, voltage across the lowest unit is 17.5 kV and string efficiency is 84.28%. The total voltage across the string will be equal to______.

a. 442.5 kV

b. 88.25 kV

c. 44.25 kV

d. 8.825 kV