Operating Voltage of the Transmission Line

To determine the operating voltage of the transmission line, we need to consider the number of discs of suspension insulator in each string.

Given that there are 9 discs of suspension insulator in each string, we can use this information to calculate the operating voltage.

Insulator Strings
- An insulator string is a set of insulator discs connected in series and used to support the transmission line conductors.
- The insulator discs are designed to withstand high voltages and provide insulation between the conductors and the supporting structure.

Voltage Rating of Insulator Discs
- Each insulator disc has a specific voltage rating, which indicates the maximum voltage it can withstand without breaking down.
- The voltage rating of an insulator disc depends on its design, material, and dimensions.
- Common voltage ratings for insulator discs include 11 kV, 33 kV, 66 kV, 132 kV, etc.

Operating Voltage Calculation
- In a transmission line, the operating voltage is determined by the voltage rating of the insulator discs used in the string.
- Since each string consists of 9 discs of suspension insulator, the operating voltage will be equal to the voltage rating of the insulator disc multiplied by the number of discs in the string.
- Therefore, the operating voltage of the transmission line can be calculated as 9 times the voltage rating of the insulator disc.

Given Data
- Number of discs in each string = 9

Options for Operating Voltage
a) 11 kV
b) 33 kV
c) 66 kV
d) 132 kV

Answer
The correct answer is option d) 132 kV.

Explanation
- Since each string consists of 9 discs of suspension insulator, the operating voltage will be 9 times the voltage rating of the insulator disc.
- None of the given options (11 kV, 33 kV, 66 kV) can be multiplied by 9 to obtain an integer value, except for 132 kV.
- Therefore, the operating voltage of the transmission line is 132 kV.