An electric generator is a device that converts mechanical energy obtained from an external source into electrical energy as the output.
Diesel Engine + Alternator = Diesel Generator
Main components of a Diesel Generator
The main components of an electric Diesel generator can be broadly classified as follows (refer to illustration above):
(1) Diesel Engine
(3) Fuel System
(4) Voltage Regulator
(5) Cooling and Exhaust Systems
(6) Lubrication System
(7) Battery Charger
(8) Control Panel
(9) Main Assembly / Frame
The diesel engine is a type of internal combustion engine, more specifically, a compression ignition engine, in which the fuel is ignited by the high temperature of compressed gas, rather than a separate source of energy (such as a spark plug).
How diesel engines work.
When gas is compressed its temperature rises. A diesel engine exploits this property in order to ignite the fuel. Air is drawn into the cylinder of a diesel engine, and compressed by the rising piston. This happens at a much higher compression rate than in a spark-ignition engine. At the top of the piston stroke diesel fuel is injected into the combustion chamber at high pressure through an atomizing nozzle. It mixes with the hot, pressurized air. The resulting mixture ignites and burns very rapidly. This contained explosion causes the gas in the chamber to expand, driving the piston down with considerable force, and creating power in a vertical direction.
The connecting rod transmits this motion to the crankshaft which is forced to turn, delivering rotary power at the output end of the crankshaft. ‘Scavenging’ – pushing the exhausted gas-charge out of the cylinder and drawing in a fresh draught of air – is done through ports or valves.
A vital component of any diesel engine system is the governor, which limits the speed of the engine by controlling the rate of fuel delivery.
The alternator, also known as the ‘genhead’, is the part of the generator that produces the electrical output from the mechanical input supplied by the engine. It contains an assembly of stationary and moving parts encased in a housing. The components work together to cause relative movement between the magnetic and electric fields, which in turn generates electricity.
(a) Stator – This is the stationary component. It contains a set of electrical conductors wound in coils over an iron core.
(b) Rotor / Armature – This is the moving component that produces a rotating magnetic field in any one of the following three ways:
(i) By induction – These are known as brushless alternators and are usually used in large generators.
(ii) By permanent magnets – This is common in small alternator units.
(iii) By using an exciter – An exciter is a small source of direct current (DC) that energizes the rotor through an assembly of conducting slip rings and brushes.
The rotor generates a moving magnetic field around the stator, which induces a voltage difference between the windings of the stator. This produces the alternating current (AC) output of the generator.