form factor of alternating current is 1.1 not 1.11, which
is the ratio of rms value to average value of alternating
current.so generation of ac voltage is in multiple of 11,
like 11kv,33kv,44kv,66kv etc

First let us define form factor before we go into the
question:

The form factor of an alternating current waveform (signal)
is the ratio of the RMS (Root Mean Square) value to the
average value (mathematical mean of absolute values of all
points on the waveform). In case of a sinusoidal wave, the
form factor is approximately 1.11.

The reason is some thing historical. 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. It has nothing to do with form factor (1.11).
Nowadays that thought has changed and we are using 400 V
instead of 440 V, or 230 V instead of 220 V.
Also alternators are now available with terminal voltages
from 10.5 kV to 15.5 kV so generation in multiples of 11
does not arise.

FORM FACTOR of sine wave is 1.11
rms/avg=(im/root2)/(2*im/pi) = 1.11
FF of square wave is 1.00 n triangular is 1.15
so i think form factor is not the only logic behind
11kv/33kv but while the generator o/p formula suggest there
are certain terms multiplied with the form factor(1.11) n
it is forcibly made to a standadadised value by changing
certain parameters..

The Basic Idea behind a desired transmission voltage was still the form factor. In ancient times when we needed to use 10 kV at destination, simply multiplied the form factor to it Say 1.11X10=1.11 =11KV aprox.(we had taken 10% losses as standard thumb rule) similarily for 30 & 60 KV.

Form Factor = RMS voltage/Average Voltage For AC sine wave Form Factor is 1.11.

Now a days when, we have voltage correction systems, powerfactor improving capacitors, which can boost/correct volatge to desired level, we are using the exact voltages like 400KV inspite of 444KV.