AC DC generator can be termed as rotating amplifier. Theoretically energy can not be generated only the energy can be converted one form to other. According to this definition DC generator convert the mechanical energy to electrical energy. The field circuit is excited, this field current is usually being small, the electric power input to the generator the electric power input to the generator is small fraction of power rating of generator on other hand armature current of generator is usually much large so electrical power output to generator is much larger then electrical input. Ratio of electric power output to electrical power input can be consider as power amplification of generator .