Number of discs in string of insulators for 400 kV AC overhead transmission lines will be in range of

Electrical Engineering MCQ on Power Transmission

Number of discs in string of insulators for 400 kV AC overhead transmission lines will be in range of:

1. 15 to 18
2. 19 to 20
3. 21 to 23
4. 23 to 30

Correct answer: 3. 22 to 23

Solution:

Each disc of string is generally designed for voltage level of 11 kV.

Voltage across string = Phase voltage = 400/√3 = 231 kV

For 11 kV per disc = 231/11 = 21

So 3. 21 to 23 is the right option