Final answer:
The rating of 645 MVA for a three-phase synchronous generator indicates its maximum apparent power output under rated conditions, essential in electrical engineering for determining the generator's capacity to supply electrical power.
Step-by-step explanation:
The rating of a three-phase synchronous generator that is rated at 645 MVA essentially means that this generator can deliver 645 Megavolt-amperes. In engineering, especially electrical engineering, this sort of rating is crucial as it defines the maximum apparent power the generator can provide operating under its rated conditions.
The power capacity, or the rating of the generator, is important for determining how much electrical power can be generated and supplied to the grid or to the electrical load it serves. Generators with a MVA rating are typically used in power stations or industrial plants where high power outputs are necessary.