The reason for these "odd" voltage figures dates back
years.The original idea was to make up for the voltage drop
in long transmission line conductors , hence 11KV was
designed to deliver 10 KV at the end of the line , 132 KV
was designed to deliver 130KV at the end of the line and so
on. It has nothing to do with form factor . Also this has
long been abandoned and nowadays the voltage supplied at
the end of the line should be the voltage stated plus or
minus a very small percentage. 400 KV voltage appeared
after this idea was abandoned , hence it is a " round "
figure . Otherwise it might have been 405 or 410 KV !
i think it is not related with form factor as many replied
because if so then why 400 kv or 765 kv is followed as
these r not multiple of 11.i think becuse of constrainst in
gen voltage that is between 10.5 to 15 kv we[earlier]to
choose 11 kv and 33 66 132 kv r multiple of 11 to suite
our transformation ratio.if once follewed it continuied
otherwise i dont find any reason that with 12 kv gen why v
cant have 44 144 kv transmission.