How Does a Generator Create Electricity?
How Generators Work
Generators are useful appliances that supply electrical power during a power
outage and prevent discontinuity of daily activities or disruption of business operations. Generators are available
in different electrical and physical configurations for use in different applications. In the following sections,
we will look at how a generator functions, the main components of a generator, and how a generator operates as a
secondary source of electrical power in residential and industrial applications.
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
The main components of an electric
generator can be broadly classified as follows (refer to illustration above):
(3) Fuel System
(4) Voltage Regulator
(5) Cooling and Exhaust Systems
(6) Lubrication System
(7) Battery Charger
(8) Control Panel
(9) Main Assembly / Frame
A description of the main components of a generator is given below.
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. There are several factors
that you need to keep in mind while assessing the engine of your generator. The manufacturer of the engine should
be consulted to obtain full engine operation specifications and maintenance schedules.
(a) Type of Fuel Used – Generator engines operate on a variety of fuels such as
diesel, gasoline, propane (in liquefied or gaseous form), or natural gas. Smaller engines usually operate on
gasoline while larger engines run on diesel, liquid propane, propane gas, or natural gas. Certain engines can also
operate on a dual feed of both diesel and gas in a bi-fuel operation mode.
(b) Overhead Valve (OHV) Engines versus non-OHV Engines – OHV engines differ from
other engines in that the intake and exhaust valves of the engine are located in the head of the engine’s cylinder
as opposed to being mounted on the engine block. OHV engines have several advantages over other engines such
• Compact design
• Simpler operation mechanism
• User-friendly in operations
• Low noise during operations
• Low emission levels
However, OHV-engines are also more expensive than other engines.
(c) Cast Iron Sleeve (CIS) in Engine Cylinder – The CIS is a lining in the cylinder
of the engine. It reduces wear and tear, and ensures durability of the engine. Most OHV-engines are equipped with
CIS but it is essential to check for this feature in the engine of a generator. The CIS is not an expensive feature
but it plays an important role in engine durability especially if you need to use your generator often or for long
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.
The following are the factors that you need to keep in mind while assessing the
alternator of a generator:
(a) Metal versus Plastic Housing – An all-metal design ensures durability of the
alternator. Plastic housings get deformed with time and cause the moving parts of the alternator to be exposed.
This increases wear and tear and more importantly, is hazardous to the user.
(b) Ball Bearings versus Needle Bearings – Ball bearings are preferred and last
(c) Brushless Design – An alternator that does not use brushes requires less
maintenance and also produces cleaner power.
(3) 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. For commercial applications, it may be necessary to erect and
install an external fuel tank. All such installations are subject to the approval of the City Planning
Division. Click the following link for further details regarding fuel tanks for generators.
Common features of the fuel system include the following:
(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.
(4) Voltage Regulator
As the name implies, this component regulates the output voltage of the generator.
The mechanism is described below against each component that plays a part in the cyclical process of voltage
(1) Voltage Regulator: Conversion of AC Voltage to DC Current – The voltage
regulator takes up a small portion of the generator’s output of AC voltage and converts it into DC current. The
voltage regulator then feeds this DC current to a set of secondary windings in the stator, known as exciter
(2) Exciter Windings: Conversion of DC Current to AC Current – The exciter windings
now function similar to the primary stator windings and generate a small
AC current. The exciter windings are connected to units known as rotating rectifiers.
(3) Rotating Rectifiers: Conversion of AC Current to DC Current – These rectify the
AC current generated by the exciter windings and convert it to DC current. This DC current is fed to the rotor /
armature to create an electromagnetic field in addition to the rotating magnetic field of the rotor /
(4) Rotor / Armature: Conversion of DC Current to AC Voltage – The rotor / armature
now induces a larger AC voltage across the windings of the stator, which the generator now produces as a larger
output AC voltage.
This cycle continues till the generator begins to produce output voltage
equivalent to its full operating capacity. As the output of the generator increases, the voltage regulator produces
less DC current. Once the generator reaches full operating capacity, the voltage regulator attains a state of
equilibrium and produces just enough DC current to maintain the generator’s output at full operating
When you add a load to a generator, its output voltage dips a little. This prompts
the voltage regulator into action and the above cycle begins. The cycle continues till the generator output ramps
up to its original full operating capacity.
(5) Cooling & Exhaust Systems
(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. Hydrogen removes heat from the generator and transfers it
through a heat exchanger into a secondary cooling circuit that contains de-mineralized water as a coolant. This is
why very large generators and small power plants often have large cooling towers next to them. For all other
common applications, both residential and industrial, a standard radiator and fan is mounted on the generator and
works as the primary cooling system.
It is essential to check the coolant levels of the generator on a daily basis. The
cooling system and raw water pump should be flushed after every 600 hours and the heat exchanger should be cleaned
after every 2,400 hours of generator operation. The generator should be placed in an open and ventilated area that
has adequate supply of fresh air. The National Electric Code (NEC) mandates that a minimum space of 3 feet should
be allowed on all sides of the generator to ensure free flow of cooling air.
(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.
Exhaust pipes are usually made of cast iron, wrought iron, or steel. These need to
be freestanding and should not be supported by the engine of the generator. Exhaust pipes are usually attached to
the engine using flexible connectors to minimize vibrations and prevent damage to the generator’s exhaust system.
The exhaust pipe terminates outdoors and leads away from doors, windows and other openings to the house or
building. You must ensure that the exhaust system of your generator is not connected to that of any other
equipment. You should also consult the local city ordinances to determine whether your generator operation will
need to obtain an approval from the local authorities to ensure you are conforming to local laws a protect against
fines and other penalties.
(6) 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
(7) 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.
(8) Control Panel
This is the user interface of the generator and contains provisions for electrical
outlets and controls. The following article provides further details regarding the generator control panel.
Different manufacturers have varied features to offer in the control panels of their units. Some of these are
(a) Electric start and shut-down – Auto start control panels automatically start your
generator during a power outage, monitor the generator while in operation, and automatically shut down the unit
when no longer required.
(b) Engine gauges – Different gauges indicate important parameters such as oil
pressure, temperature of coolant, battery voltage, engine rotation speed, and duration of operation. Constant
measurement and monitoring of these parameters enables built-in shut down of the generator when any of these cross
their respective threshold levels.
(c) Generator gauges – The control panel also has meters for the measurement of
output current and voltage, and operating frequency.
(d) Other controls – Phase selector switch, frequency switch, and engine control
switch (manual mode, auto mode) among others.
(9) Main Assembly / Frame
All generators, portable or stationary, have customized housings that provide a
structural base support. The frame also allows for the generated to be earthed for safety.
Using Generators to Power Residential & Industrial
While the underlying principle of operation to generate electricity remains more or
less the same in all kinds of generators, the mechanism of powering up your application using the generator’s
electrical output varies a little from one system to the other.
These are usually used for residential
purposes to power a few domestic appliances during an outage or at construction sites that have no source of
electrical power required to operate tools like drills, saws and paint sprayers. You would usually require systems
that generate at least 4 kilowatts (kW) of power.
Use of Extension Cords:
One of the most economical ways to ensure power supply during an outage is to use
extension cords to directly connect a portable generator to power the chosen appliances in your
Use of Power Transfer Switch:
A safer way to use a portable generator is to have a power transfer switch installed
and connected to the main electrical panel of your house. As the name implies, a power transfer switch enables
switching from a primary power source, usually the utility power, to a secondary or tertiary power source such as
the generator when supply from the primary source is interrupted. Manual switches are operated through direct
manipulation or by using a remotely wired control device. During a power outage, the transfer switch isolates the
electrical panel from utility supply and connects it to the generator.
The generator can then be connected to the power transfer switch through an
extension cord. Electrical output from the generator can then be fed into circuits through the main circuit breaker
and used to power the required circuits. Critical and non-critical circuits of the panel can be grouped
individually and separately wired such that the portable generator powers only the critical section as
Isolating the utility lines from the generator source also eliminates the risk of
‘back feed’. Back feed is the flow of electrical power from the generator into the utility lines, which can be
fatal to electricians working on utility lines during an outage.
Residential Standby Generators
A portable generator is limited in utility since it can power only a few appliances. An emergency
residential standby system can be used to deliver power for the entire household and can even keep air conditioners
operational during a power outage. You can also choose smaller standby units to power only a few circuits to keep
essential appliances like refrigerators, lights and fans running during an outage. These units typically range in
power generation capacity from 6 kW to 40 kW.
Use of Automatic Transfer Switch
Standby generators are usually installed outside the home and are connected to the
main electrical panel through an automatic transfer switch. The system automatically restores power to the
household within about 20 seconds of a power failure without any manual intervention.
Commercial Standby / Industrial Generators
Industrial generators are used in commercial facilities such as corporate offices,
manufacturing plants, mining operations, nursing homes, data centers, hospitals and so forth that simply cannot
afford the risk of discontinuity in business operations during a power failure. These are often stationary units
that produce anywhere from 50 kW up to 2000 kW of power. Most smaller and residential generators are
single-phase (120 Volts), but commercial generators are almost always three-phase (120, 240 or 480
Use of Automatic Transfer Switch
Similar to residential standby systems, commercial standby / industrial generators
are wired to the main electrical panel of the building through an automatic transfer switch and are fired
automatically during a power outage. These are specially designed such that switching between the primary and
secondary sources of power takes only about a fraction of a second and practically allows for seamless supply of
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