Why Electric Power Transmission is Multiple of 11 i.e 11kV, 22kV, 66kV etc?

In olden days when the electricity becomes popular, the people had a misconception that in the transmission line there would be a voltage loss of around 10%. So in order to get 100 at the load point they started sending 110 from supply side. This is the reason.

In case of no load, there may be negligible voltage drop and we may get 110% (i.e. Sending + 10% extra which is 11kV) voltage at the receiving point. For this reason, transformer and substation should be rated at full 110% which is 11kV, 22kV and so on.

Earlier days, electricity board had planned to deliver the voltage level of 10 kv, 20 kv, 30 kv,120 kv at the receiving end, this is their ultimate aim. 

Also, we know the transmission loss and voltage drop occurs due to the line resistance. 

So they had planned to deliver the desired voltage with 10 % as extra (110%) to match the transmission loss and line drop. Lets see the calculation

10 KV X 110% = 11 KV

20KV X 110% = 22 KV

30 KV X 110% = 33 KV

60 KV X 110% = 66 KV

100KV X 110% = 110KV

120 KV X 110% = 132KV

Here the 10 % consider as line drop. Thats why in India 11kV, 22kV, 33kV, 66kV, 132kV

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