Since the voltage output of the generator is essentially constant, the amount of current flow produced by the generator is directly related to the generator load at that particular point in time.
For example: If a 100 megawatt generating unit is producing 26 megawatts at 13,000 volts, it is running at 26 percent of capacity. We can use Watts Law -- Wattage equals Voltage times Current -- to calculate how much current flow or amperage exists at 13,000 volts. At 26 megawatts, we simply divide 26,000,000 watts by 13,000 volts. The current being produced is therefore 2,000 amps. All generators have a maximum amperage flow capability.