说明：  A generator is an autonomous device capable of generating electricity. Most groups consist of a heat engine that drives an alternator. Their size and weight can vary from a few kilograms to several tens of tons. The power of a generator is expressed in VA (voltampere), kVA (kilovoltampere) or MVA (megavoltampere) depending on the power. The most powerful units are driven by gas turbines or large diesel engines.