Answer: any electrical equipment, in order to work safely and reliably, must have certain current, voltage and power factor limit and prescribed value, which is called the rated value.
Answer: when the load of the star connection is asymmetrical, if the impedance of the middle line or the middle line is larger, the neutral point voltage will appear, which is called the neutral point displacement.
Answer: generator overload should cause stator and rotor winding and core temperature rise, accelerate insulation aging. But the aging of insulation requires a time process, and requires a process of high temperature. The shorter the high temperature time, the less damage to the insulation material, the generator's full load temperature and the allowable temperature, even if the overload will not exceed a lot, so the generator allows short time overloading.