why nearly all the voltage levels are in the multiples of 11
like 3.3 ,6.6 ,33 ,11 kv.....

Answer Posted / k.sahadevan nair

In India and other commonwealth countries, in the initial stage maximum generation voltage was 11 KV considering maximum available insulation rating. In order to step up this voltage,secondary of transformers should be 33 KV, 66 KV, 110 KV ,132 KV, 220 KV etc. So HT voltage of all step up/down transformers were fixed at multiples of 11. This has become a practice. This has nothing to do with form factor 1.11
When generation voltage is improved due to advancement of technology it has become difficult to change rating of all existing transformers. Naturally rating of transmission voltage of multiples of 11 continued and still going on. This is not applicable to EHT as this is a recent development and limited to certain countries only.

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