Most electric generators are based on magnetic induction motor, comprised of two parts:
1) rotation of generator by an external force such as gas, steam, or hydro input energy and
2) generation of electrical energy. MTG is driven by permanent magnets built on the rotor, coils, and control circuits to dynamically switch N and S polarity.
Therefore, no external energy input is required. It is equipped with a small battery only to initiate a rotation of the generator as well as to supply the base current for electronic control circuits.