What is a diesel generator? How does it work? What is it used for?

What is a diesel generator?

A diesel generator is a mechanical-electrical machine that produces electrical energy (electricity) from diesel fuel.  They are used by the residential, commercial, charitable and governmental sectors to provide power in the event of interruption to the main power, or as the main power source.

They can be turned on and off in just a few seconds, meaning they are able to respond quickly and using a liquid fuel, they can run for many hours uninterrupted.

Diesel generators have the same main components from the smallest portable unit, to the largest units in power plants. Have a look at a diesel generators major components.

How does a diesel generator work?

A Diesel Generator works by converting chemical energy present in diesel fuel into mechanical energy by using a diesel engine. As the engine runs, chemical energy stored within the diesel fuel is converted to mechanical energy, in the form of a rotating shaft. The engine is usually directly coupled to a single bearing alternator via the engine flywheel, but sometimes in the case of two bearing alternators via a flexible coupling.  As the engine rotates, the alternators main rotor spins as the power is transmitted through the mechanical coupling, creating electrical energy in the form of a voltage at the alternator terminals. This energy is produced by a magnetic field from the main rotor inducing a current in the main stator, as the magnetic flux associated with its windings dissects the magnetic field of the stator windings.

The coiled windings, usually made from copper due to its low electrical resistance are in turn connected to the alternators terminals. The electrical load is then in turn connected to the terminals, usually via a switching device such as a MCB, MCCB or ACB.

Generators when used as standby, usually have something called a Transfer Switch. This is a mechanical device that stops the generator being connected to the load at the same time as the mains power supply. When the mains power is present, connecting a generator at the same time needs to be done with special controls to run them in parallel. Without this control system, serious damage to the generator can occur, leading to fires. When the mains supply has failed, connecting a generator without isolating it from the mains will lead to back-feeding the grid - potentially killing someone working on restoring the mains supply and probably damaging your generator when the mains returns.

When used as the prime source of power (for example when there is no mains supply, or the mains is too poor to be used) this is referred to as "Island Mode". Where larger requirements for power exist, multiple smaller units can be connected together in parallel, by using a process known as synchronizing.

Do they require maintenance?

Diesel generators require careful routine maintenance at regular intervals. This depends on the manufacturer, but the most important item to be serviced typically is the engine. Engines normally require servicing after 250 or 500 hours, but the service interval is defined by the engine manufacturer. If you relate this to a car, driving at 50mph or 80kph, at 500 hours, that would equate to 25,000 miles or 40,000km!

Typically on a routine service you will do a thorough check, change the air filter, oil filter and fuel filter, replace the oil and some of the belts, such as the radiator fan belt and the charging alternator belt.

Maintaining your generator is an important part of ensuring it delivers the electrical power when you need it!

What is a diesel generator used for?

The electrical load is then used to power devices in your home, office, school, factory or any other installation that requires electrical power. Generators can be used at different ratings depending on the application such as Prime (PRP), Standby (ESP), Continuous (COP) or Limited Time (LTP).

Sometimes a diesel generator can be cheaper than the mains electricity, but normally it is a more expensive option.