LESSON 6: PRINCIPLES OF OPERATION OF MOTORS AND GENERATORS (PART TWO)
How
Does a Generator Create Electricity? How Generators Work
How does a generator work?
An
electric generator is a device that converts mechanical energy obtained from an
external source into electrical energy as the output.
It is important to understand that a generator does not actually
‘create’ electrical energy. Instead, it uses the mechanical energy supplied to
it to force the movement of electric charges present in the wire of its
windings through an external electric circuit. This flow of electric charges
constitutes the output electric current supplied by the generator. This
mechanism can be understood by considering the generator to be analogous to a
water pump, which causes the flow of water but does not actually ‘create’ the
water flowing through it.
The modern-day generator works on the principle of
electromagnetic induction discovered by Michael Faraday in 1831-32. Faraday
discovered that the above flow of electric charges could be induced by moving
an electrical conductor, such as a wire that contains electric charges, in a
magnetic field. This movement creates a voltage difference between the two ends
of the wire or electrical conductor, which in turn causes the electric charges
to flow, thus generating electric current.
Main
components of a generator
The main components of an electric generator can be broadly classified
as follows:
- Engine
- Alternator
- Fuel
System
- Voltage
Regulator
- Cooling
and Exhaust Systems
- Lubrication
System
- Battery
Charger
- Control Panel
- Main Assembly / Frame
A description of the main components of a generator is given
below.
Engine
The engine is the source of the input mechanical energy to the generator. The size of the engine is directly proportional to the maximum power output the generator can supply.
Alternator
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.
Fuel System
The fuel tank usually has sufficient capacity to keep the generator operational for 6 to 8 hours on an average. In the case of small generator units, the fuel tank is a part of the generator’s skid base or is mounted on top of the generator frame.
(a) Pipe connection from fuel tank to
engine – The supply line directs fuel from the tank to the engine and the
return line directs fuel from the engine to the tank.
(b) Ventilation pipe for fuel tank – The fuel tank has a ventilation pipe to
prevent the build-up of pressure or vacuum during refilling and drainage of the
tank. When you refill the fuel tank, ensure metal-to-metal contact between the
filler nozzle and the fuel tank to avoid sparks.
(c) Overflow connection from fuel tank to the drain pipe – This is required so
that any overflow during refilling of the tank does not cause spillage of the
liquid on the generator set.
(d) Fuel pump – This transfers fuel from the main storage tank to the day tank.
The fuel pump is typically electrically operated.
(e) Fuel Water Separator / Fuel Filter – This separates water and foreign
matter from the liquid fuel to protect other components of the generator from
corrosion and contamination.
(f) Fuel Injector – This atomizes the liquid fuel and sprays the required
amount of fuel into the combustion chamber of the engine.
Voltage Regulator
As the name implies, this component regulates the output voltage of the
generator.
Cooling & Exhaust System
(a) Cooling System
Continuous usage of the generator causes its various components to get heated
up. It is essential to have a cooling and ventilation system to withdraw heat
produced in the process.
Raw/fresh water is sometimes used as a coolant for generators, but these are mostly limited to specific situations like small generators in city applications or very large units over 2250 kW and above. Hydrogen is sometimes used as a coolant for the stator windings of large generator units since it is more efficient at absorbing heat than other coolants.
(b) Exhaust System
Exhaust fumes emitted by a generator are just like exhaust from any other
diesel or gasonline engine and contain highly toxic chemicals that need to be
properly managed. Hence, it is essential to install an adequate exhaust system
to dispose of the exhaust gases. This point can not be emphasized enough
as carbon monoxide poisoning remains one of the most common causes for death in
post hurricane affected areas because people tend to not even think about it
until it’s too late.
Lubricating System
Since the generator comprises moving parts in its engine, it requires
lubrication to ensure durability and smooth operations for a long period of
time. The generator’s engine is lubricated by oil stored in a pump. You should
check the level of lubricating oil every 8 hours of generator operation. You
should also check for any leakages of lubricant and change the lubricating oil
every 500 hours of generator operation.
Battery Charger
The start function of a generator is battery-operated. The battery charger
keeps the generator battery charged by supplying it with a precise ‘float’
voltage. If the float voltage is very low, the battery will remain
undercharged. If the float voltage is very high, it will shorten the life of
the battery. Battery chargers are usually made of stainless steel to prevent
corrosion. They are also fully automatic and do not require any adjustments to
be made or any settings to be changed. The DC output voltage of the battery
charger is set at 2.33 Volts per cell, which is the precise float voltage for
lead acid batteries. The battery charger has an isolated DC voltage output that
does interfere with the normal functioning of the generator.
Control Panel
This is the user interface of the generator and contains provisions for
electrical outlets and controls.
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