It is not true that all the transmissions and distribution voltages are multiple of 11. In most cases, they are multiple of 11 such as 11kV, 22kV, 33kV, 66kV & 132kV. But 400kV, 765kV, and 800kV etc. are not multiple of 11.

The form factor of an alternating current waveform (signal) is the ratio of the RMS (Root Mean Square) value to the average value of electrical quantity. In the case of a sinusoidal wave, the form factor is approximately 1.11.

Now, we know that 400kV and 800kV are not multiples of 11. Also,

10kV x 1.11 = 11.1kV (But the transmitted voltage is 11kV)

20kV x 1.11 = 22.2kV (But the transmitted voltage is 22kV)

30kV x 1.11 = 33.3kV (But the transmitted voltage is 33kV)

60kV x 1.11 = 66.6kV (But the transmitted voltage is 66kV)

120kV x 1.11 = 133.2kV (But the transmitted voltage is 132kV)

The above calculation clearly shows that the results are different than the general values i.e., in case of 132kV, with the form factor multiplication, it is 133.2kV.

But on higher voltage levels we can see how values aren’t matching with the real situation. 66kV is not equivalent to 66.6kV and in the case of 132kV, we can see the value comes out to be 133.2kV which is 1.2kV more than the line voltage of 132kV. In the same way, as we go ahead, we will find this voltage divergence increasing which brings us to the conclusion that the form factor has nothing to do with line voltage value.

In addition, we use 230V instead of 220V (Single Phase) and 400V instead of 440V (Three Phase).

Also, alternator and generator with terminal voltages are available in the range of 10kv – 15kV which is not having to do with multiple of 11.

Now back to the point, the voltage at the receiving end is generally:

10kV

20kV

30kV

60kV

120kV and so on…

But we already know that there are some voltages drop due to the resistance of the transmission lines at receiving end. For this reason, they transmit 10% extra voltage. A transmission line travels over a long distance and therefore various factors lead to a drop in the line voltage which is undesirable because it causes poor voltage regulation of the line. To counter this problem, a 10% voltage compensation technique was employed in which the transmission line voltage was boosted to an extra 10% of the target so that the target voltage remains constant.

For example:

Sending Voltage = 10kV x 10% = 11kV. While the receiving end voltage is 10kV due to voltage drop.

Sending End Voltage & Receiving End Voltage

10kV x 10% = 11kV = 10kV

20kV x 10% = 22kV = 20kV

30kV x 10% = 33kV = 30kV

60kV x 10% = 66kV = 60kV

120kV x 10% = 132kV = 120kV

200kV x 10% = 220KV = 200KV

In modern, electrical power is transmitted at 400KV - 800KV. The 10% extra voltage compensation technique is not applicable to these Voltages because these voltages are very higher and voltage drops are negligible at a higher voltage.