The value of form factor is 1.1 which is calculated for the
sine wave. At this value of form factor, leakage flux is
minimum and efficiency is maximum for any electrical
machines. These machines are operated at sine waves.
At the time of generation there are many type of losses
therefore earlier use to write 10(+/- 1%)kv so thats why we
generally use to write it as 11kv.Since our ancestral make it
a standard of 11kv,33kv,66kv and as the year pass,many
engineers added a new myth of form factor,10% loss of actual
power.....and thus it make us to suffer a lot.
Since there is 230kv and still like 765kv which are not
multiple of 11.
and production in 11kv and 33kv is more ecnomical