Electrical energy is one of the most important sources of energy in modern society. The generator is a mechanical device that converts other forms of energy into electrical energy. It was first produced during the second industrial revolution. It was made by German engineer Siemens in 1866. It was driven by a hydraulic turbine, a steam turbine, a diesel engine, or other power machinery. The energy produced by air flow, fuel combustion, or nuclear fission is converted into mechanical energy that is transmitted to a generator and then converted into electricity by a generator. Generators have a wide range of uses in industrial and agricultural production, national defense, technology and daily life.