How does a Diesel Generator Work?

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Diesel generators – sometimes called ‘gensets’ – are relied upon by many businesses and other organisations to supply the electrical power they need during cuts, brownouts, or any other interruption to mains power. There are many different types and configurations of generators, but they all work essentially the same way, and have the same core components.


How does a Diesel Generator create Electricity?

A diesel generator converts mechanical energy (movement) into electrical power, and channels it through power cables. It can be helpful to imagine electricity flowing through wires in much the same way water flows through pipes. A generator can be thought of as a kind of ‘electrical pump’ which causes the electricity to flow through the wires. It doesn’t actually create or destroy the electrons that flow through the wires any more than a water pump creates new water. It just causes it to move in a useful fashion.


The main Components of a Diesel Generator

The Engine

This is typically a diesel engine, much like that in a large vehicle, the bigger the source of mechanical energy, the more electrical power can come out ‘the other end’.

The Alternator

This is the part which turns the mechanical energy (the rotation of the shaft) into electrical power through induction. The ‘how’ of the alternator is one of the most fascinating parts of a generator. Faraday discovered (or at least described) the process of ‘electromagnetic induction’ in the early 1830s. This principle holds that if you move a wire (or any electrical conductor) through a magnetic field, an electric current is ‘induced’ in the wire. The same is true if the wire is still and the magnetic field moves. Simply moving through a magnetic field causes the electrons to flow through the wire. If the wire moves north-south, the electrons flow one way, and if it moved back south-north, they flow into the other. The stronger the field and the longer the wire, the greater the amount of current induced. Modern generators work by placing several large, powerful magnets in a cluster around a central, rotating shaft. This is called the ‘rotor’ or ‘armature’. The magnets might be permanent magnets or electromagnets, but the point is that they produce a magnetic field, which the engine causes to turn. The other important sub-component of the alternator is the ‘stator’, which is essentially a series of tightly bundled coils of wire, all packed closely around the rotor. When an outside force (such as a diesel engine) turns the central shaft, the rotor constantly moves the north and south poles of its magnetic field(s) across the bundles of wire that surround them. This causes a great deal of electrical current to flow back and forth through the wires – what we call ‘alternating current’ or ‘AC’ mains power.

The Fuel System

This is typically the diesel fuel supply for the engine. The most obvious part is a tank holding enough fuel for at least 6-8 hours of operation. This tank may be inside the generator housing for smaller, or portable units, or it may be a separate external structure for larger, permanently installed units. Other parts of the fuel system involve pipe-work to get the fuel to the engine, a fuel pump similar to the one in most vehicles, a fuel filter, and a ventilation pipe or valve for the fuel tank, preventing overpressure or vacuum inside. There will also be an overflow connection ensuring that if the tank is overfilled, the fuel ischannelledaway, and not simply splashed over the surface of the engine or alternator.

The Voltage Regulator

This is a fairly complex but important component. Without it, the voltage and amperage of the AC current provided would vary according to the speed of the engine. As modern electrical equipment relies on a very steady power supply, something is required to level it out. The workings of a voltage regulator are quite ingenious and are beyond the scope of this article. It is probably enough to know what it does, for now.

The Cooling System

Just like in a vehicle, the engine produces a great deal of waste heat in addition to mechanical energy. The power flowing through the alternator also produces heat via the electrical resistance of the wires themselves. Again, like in your car, this heat is soaked up by a coolant fluid, often but not necessarily water, which then runs through a heat exchanger, dumping its heat typically into the air, or sometimes into a secondary coolant fluid.

The Exhaust System

All internal combustion engines produce exhaust gases. These are toxic and must be directed away from the engine itself and any nearby people. Exhaust gases are typicallychannelledthrough pipes, and vented into the outside air. There are typically health and safety regulations about how and where exhaust systems must bechannelled, so consult these carefully before installing a new generator.

The Lubrication (oil) System

Any engine requires lubrication, and this is handled by an oil pump and reservoir attached to the engine itself.

The Starter & Battery System

Again, just like in a car or lorry, the diesel motor relies on a small electrical motor to start running. This electrical starter motor is powered by a battery, which is charged by either a separate charger or the generator output itself.

The Control Panel

The control panel is where the generator is operated. Typical controls & outputs included on most control panels are:

  • Start / shutdown controls (manual, automatic, or both)
  • Phase selector switch
  • Frequency switch
  • Engine mode switch
  • Engine fuel
  • Engine oil
  • Engine speed
  • Coolant temperature
  • Battery charge
  • Generator output voltage
  • Generator output current (amperage)
  • Generator Output in kVA
  • AC power frequency

The frame/Housing

Thegensetwill either be contained in a weatherproof housing, an open structural frame, or a transportable unit. All of these function to keep the components together and solidly attached. It also ensures that all electrical components are safely grounded.

The Canopy

A diesel generator can also be covered in an acoustically treated canopy which dramatically reduces the dB level, even from within as little as a meter away, the engine noise can be very little. A generator with an acoustic canopy covering the other elements is often referred to as a Silent Generator.