Reason for Generation of Alternator Voltage is 22KV.
Generator current depends on the power output, if the power is more current will be more. Stator current can be reduced by increasing the generator voltage, but there is limit for increasing the voltage due to the insulation of stator i.e. if the voltage is too high insulation level is too thick and machine size will be too big and costlier that is why generation voltage is between 11 KV to 22 KV.
The standard frequency of the alternator is 50 Hz in India and 60Hz in North America. These frequencies require rotational speeds of 3000 rpm and 3600 rpm respectively for a two pole alternator.
The power outputs of alternators are limited by the rate at which heat can be dissipated as it is produced by heavy currents flowing in their coils.
In the case of an alternator with an output of 660 MW at 22KV the stator current is 30,000 amps. Since overheating could damage the insulation and cause short circuits, developments in alternator output have occurred through improvements in cooling.
In future, it might be possible to increase output considerably by using high-temperature superconducting coils, whose lack of resistance would remove the mechanism by which heat is generated in the alternator. This improvement would allow the construction of more compact generators of high efficiency.