Why you transfer voltage is 11kv33kv66kv?

All sinusoidal AC voltages are multiples of 1.1. This is due to the form factor, which is the ratio of the quadratic mean value of the voltage with the average voltage, which is pi/2√2=1.1 (approximately). It also provides the most economic means of constructing step up/down Transformers.

In the UK, 33 kV (along with 66 kV) is considered to be a primary distribution voltage level, whereas 11 kV is secondary distribution voltage level. Incidentally, the correct symbol for 'kilovolt' is 'kV', not 'kv'.