In addition to the engine and generator, engine-generators generally include a fuel tank, an engine speed regulator and a generator voltage regulator, cooling and exhaust systems, and lubrication system. Units larger than about 1 kW rating have a battery and electric starter; very large units may start with compressed air. Standby power generating units often include an automatic starting system and a transfer switch to disconnect the load from the utility power source and connect it to the generator.
Engine-generators are used to supply electrical power in places where utility (central station) power is not available, or where power is needed only temporarily. Small generators are sometimes used to supply power tools at construction sites. Trailer-mounted generators supply power for temporary installations of lighting, sound amplification systems, amusement rides etc.
Standby power generators are permanently installed and kept ready to supply power to critical loads during temporary interruptions of the utility power supply. Hospitals, communications service installations, data processing centers, sewage pumping stations and many other important facilities are equipped with standby power generators.
Privately-owned generators are especially popular in countries where grid power is undependable or unavailable. Trailer-mounted generators can be towed to disaster areas where grid power has been temporarily disrupted.
Engine-generators are available in a wide range of power ratings. These include small, hand-portable units that can supply several hundred watts of power, hand-cart mounted units, as pictured below, that can supply several thousand watts and stationary or trailer-mounted units that can supply over a million watts. The smaller units tend to use gasoline (petrol) as a fuel, and the larger ones have various fuel types, including diesel, natural gas and propane (liquid or gas). The engine can also operate on diesel and gas simultaneously (bi-fuel operation).
There are only a few portable three-phase generator models available in the US. Most of the portable units available are single phase power only and most of the three-phase generators manufactured are large industrial type generators.
Portable engine-generators may require an external power conditioner to safely operate some types of electronic equipment. Small portable generators may use an inverter. Inverter models can run at slower RPMs to generate the power that is necessary, thus reducing the noise of the engine and making it more fuel-efficient. Inverter generators are best to power sensitive electronic devices such as computers and lights that use a ballast.
The mid-size stationary engine-generator pictured here is a 100 kVA set which produces 415 V at around 110 A per phase. It is powered by a 6.7 litre turbocharged Perkins Phaser 1000 Series engine, and consumes approximately 27 litres of fuel an hour, on a 400 litre tank. Diesel engines in the UK run on red diesel and rotate at 1500 or 3000 rpm. This produces power at a frequency of 50 Hz, which is the frequency used in the UK. In areas where the power frequency is 60 Hz (United States), generators rotate at 1800 rpm or another divisor of 3600. Diesel engine-generator sets operated at their peak efficiency point can produce between 3 and 4 kilowatthours of electrical energy for each litre of diesel fuel consumed, with lower efficiency at part load.