Transmitting electricity at high voltage reduces the fraction of energy lost to resistance, which varies depending on the specific conductors, the current flowing, and the length of the transmission line. For example, a 100-mile (160 km) 765 kV line carrying 1000 MW of power can have losses of 1.1% to 0.5%.
All electrical devices that supply power are usually rated in kVA. but generator put supply power in kVA because KVA is "apparent power" which does not take an account of power factor and KW is "true power". They generated own power factor
like :
VA = E X I
W = E X I COS PHI