Every generator has a required operating temperature. If it exceeds this temperature, the life of the generator will be significantly reduced. If the temperature is too high, the generator may burn. Therefore, there is an allowable temperature increase for the generator. The higher the generator load (the greater the current it generates, also called the greater power), the higher the generator temperature.
When the generator coolant temperature is lower than the rated value, it means that the generator can have a larger temperature rise, so the generator can have a larger current. His efforts multiplied.