An electrical generator is a device that converts mechanical energy to electrical energy. The source of mechanical energy may be a steam engine, a water turbine, an internal combustion engine, a wind turbine, or compressed air.

The generator works by moving electric current which is already present in the wire. There are two main parts of a generator: mechanical and electrical. The mechanical part of the generator include the rotor and stator. The rotor is the rotating part and the stator is the stationary part. On the other hand, the electrical parts include the armature, which is the power-producing component of the generator, and field, which is the magnetic field component.

An engine-generator is a combination of a generator and an engine. This is also sometimes referred to simply as a generator. These generators comprise of a fuel tank, an engine speed regulator, generator voltage regulator, exhaust system, and lubrication system.

These kinds of generators are used to supply electrical power where electricity is not available or when it is needed temporarily. Standby power generators are permanently installed and kept ready to supply power during temporary electrical interruptions. Industries usually equip themselves with standby power generators.

Smaller engine-generators use gasoline as fuel, while larger ones uses various types like propane and natural gas. Inverter generators run at slower revolutions to reduce noise and for fuel efficiency. They are advised to use on sensitive electronic devices such as computers.