Electric Generator Meaning, History, and Working Principle

An electric generator is a device or system that uses electromechanical and electromagnetic principles to convert mechanical energy to electricity. The use of generators in electricity generation is a common practice in many parts of the world. This article discusses electric generator meaning, history, and working principle, as outlined below;


-Electric Generator Meaning: 6 Definitions of the Electric Generator

-History and Origin of the Electric Generator

-Electric Generator Working Principle: How Electric Generators Work









Electric Generator Meaning: 6 Definitions of the Electric Generator

An electric generator is a device which converts mechanical energy to electricity which can be used externally for various purposes.

The above definition implies that the electric generator carries out an opposite function to that of the electric motor, which basically converts electricity to mechanical energy [7].

However, both devices (electric generator, electric motor) are similar in that they depend on electrical, mechanical and magnetic interactions as well as conversions, to function.

The following definition addresses these aspects of the electric generator.

An electric generator is a device which generates electricity through the interaction between electric charges and magnetic fields, that are creates through electromechanical and electromagnetic conversions.

Although the most common conversion sequence for an electric generator is mechanical energy to electricity, a more holistic outline of the conversions and processes involved in the process of generating electricity, can be used to define the electric generator;

Electric generator is a system equipped with components that help to convert heat energy from a fuel, to mechanical energy in the form of rotary motion, and subsequently to electricity, by combustion, pressure application, and electromagnetic induction.

It is important to note that the conversions in an electric generator may vary based on differences in the type and design of the generator, the fuel, and other operational conditions.

Because of this potential variability, the electric generator may also be referred to as an ‘energy converter’.

The components of an electric generator can also be included in the definition, as follows;

An electric generator is a device which comprises of an engine, fuel system, alternator, voltage regulator, control panel, lubrication system, cooling and exhaust system, and main frame, that work in combination to generate electricity from mechanical energy.

While generators are mostly associated with non-renewable energy technology, they are found in some renewable energy systems. This fact is portrayed in the next definition;

Electric generator is a device that generates electricity from mechanical energy which may be provided by a non-renewable resource like fossil fuel, or a renewable resource like solar, geothermal, wave, hydro and wind.

Lastly, we may define an electric generator on the basis of input and output factors, as follows;

An electric generator is a device that uses mechanical energy input from a fuel, to produce electric current output that can be used to power appliances.


History and Origin of the Electric Generator

The development of the electric generator was a major aspect of the industrial revolution, as it enabled new technologies to harness electricity derived from fossil fuels, and thereby led to overall economic and industrial growth.

In the eighteenth century, modifications of the steam engine contributed to increasing the efficiency of electric generator technology.

Notable effort in this area was made by James Watt, who developed a modified version of the steam engine in 1781 [14].

While the available technologies during this period did not bear much operational similarity to the electric generator, they gave insight to the overall mechanism required to make generators efficient.

The most important step in the development of electric generator technology, was arguably made by Michael Faraday, when he conducted experiments and made observations with regard to electromagnetism in the early 1830s [13].

Based on these observations, the first modern electromagnetic principle; Faraday’s Law, was established. This law summarized Faraday’s main discovery, that electric current can be produced from mechanical energy in a magnetic field.

Faraday’s Law highlighted a variety of concepts that include electromotive phenomenon, electromagnetic induction, and electromechanical interaction. Each of these concepts is vital to the operation of an electric generator.

The Faraday disk was designed based on the same observations, and can be described as an early, primitive precursor to the modern electric generator. It comprised of a spinning copper disc within the magnetic field created by a horseshoe magnet.

Michael Faraday's electric generator
Faraday Disk was a Precursor to the Modern Electric Motor (Credit: Daderot 2013 .CC0 1.0.)


Many faults were identified in the Faraday disk, including DC current interference, low efficiency, low output voltage, energy wastage, and weak electromagnetic induction. Identification and assessment of these faults helped in the subsequent improvements which were made.

Several accounts suggest that the phenomenon of electromagnetism was also observed independently by American scientist Joseph Henry within the same period as it was observed by Faraday [12].

Early models of the electric generator produced direct current; DC. Following Faraday’s success with electromagnetism, the French instrument designer and engineer Hippolyte Pixii, built one of the first-recorded dynamo generators in 1832 [1].

Even before the publication of the electromagnetic discoveries, in 1827 Anyos Jedlik commenced his experimental studies of electromagnetism and electromechanical systems [11]. These led to the development of the ‘electric starter’, an electromagnetic rotor, in the early 1850s.

Antonio Pacinotti built a DC dynamo in 1860 [9], which was one of the earliest stable-output DC generators.

Subsequent dynamo generators within this period, closely resembled Pixii’s model, until Werner von Siemens, Charles Wheatstone and Samuel Alfred Varley invented a more practical and efficient dynamo electric generator, which was patented in late 1866.

The dynamo electric generator gave insight into electromagnetic technology and systems designs, like electromagnets and metallic windings.

Notable improvement in electromagnetic components of the electric generator, was made, beginning from the year 1870. Zenobe Gramme modified the electromagnet to include a solid ferromagnetic core, in 1871 [3].

This change helped electric generator technology to become much more efficient, by strengthening the effect of electromagnetic inductance. It also enabled electric generators to become commercially viable, by proving the potential of the device for electricity generation.

Due to a temporary exponential increase in public interest, numerous models of the dynamo electric generator were developed after Gramme’s modification. One of these was an early AC generator, designed by Charles F. Bush in the year 1876 [6], which was a moderate commercial success.

In 1882, Thomas Edison invented a model of the DC generator, which was put into practical use in New York, United States [5]. This was one of the last developments made in the field of DC electricity generation.

Alternator systems were first demonstrated by a Westinghouse Electric engineer; William Stanley Jr., in 1886 [2]. Further work led to the development of the polyphase alternator in 1891, which was an improved alternator system for generating multiphase alternating current.

Modifications of electric generator technology in the late nineteenth, the twentieth, and the twenty-first centuries, have mainly involved efforts to improve AC generators, with the outcomes of such efforts including polyphase, large-polyphase, and magnetohydrodynamic generators.


Electric Generator Working Principle: How Electric Generators Work

The electric generator works based on the principle of electromagnetic induction, by which an electric current is produced from mechanical energy, under the influence of a magnetic field [4].

There are three (3) main steps in the operation of an electric generator, which are energy supply, energy conversion, and electromagnetic induction.

It is important to note that some similarity exists between the working principle and operational sequence of an electric generator and electric motor.

Essentially, the electric motor operates by the same electromagnetic induction principle as the electric generator, and its sequence of operation is a direct reversal of the sequence involved in electricity generation.

For electric motors, electromechanical conversion enables electricity to be converted to mechanical energy, whereas mechanical energy is converted to electricity in the generator.

Each main step in the operation of an electric generator is discussed below;


1). Energy Supply (Step 1)

Energy supply is the stage in which energy is initially derived from its primary source, by the generator.

Parts of an electric generator which are actively involved in this stage include the fuel system, and the engine.

The energy source may be renewable or non-renewable. For renewable energy sources, examples include biomass, nuclear fuel (occurs in finite amount but may be classified under renewable sources), solar, wind, geothermal and hydro. Non-renewable sources are mainly fossil fuels like diesel, coal, and natural gas.

In order for the energy source to be effectively harnessed, a mechanism or process for energy derivation or recovery must be used. This mechanism is usually combustion, which leads to thermal breakdown of the energy source (fuel) to release energy.

Power output of an electric generator depends on the amount of energy which was supplied, and how effectively this energy was used.

This means that an electric generator should ideally be equipped with systems and mechanisms that minimize energy loss and optimize energy utilization. Cogeneration systems usually include equipment that recover lost energy (in the form of heat), in order for it to be reused.

The efficiency, size, effectiveness production capacity, and complexity of the engine of electric generator, determine how well energy supply will be optimized. Generators equipped with high-capacity, high-efficiency engines generally tend to optimize energy supply and power output better than the less-efficient ones.  

2). Energy Conversion (Step 2)

During energy conversion, the heat energy derived from the fuel is transformed or converted to mechanical energy, which is used to spin a conductor (rotor, armature) in a magnetic field.

The mode of energy conversion varies, depending on the type of electric generator, engine, and primary energy source.

For turbine generators that depend on nuclear, biomass, or fossil fuels, heat energy is converted to mechanical energy, by heating  fluid like water to produce steam or other pressurized materials, which are used to push and spin the blades and shaft of the turbine [10].

steam turbine electric generator
Turbine Electric Generator Performs Thermo-mechanical Conversion using Fluids (Credit: Siemens 2005 .CC BY-SA 3.0.)


In internal combustion engines (ICEs) heat energy is converted to mechanical energy by heating a fluid in the combustion chamber, thereby causing the fluid to expand and exert pressure on a moveable component of the electric generator [8].

The fluid in the combustion chamber is usually air, while the moveable component may be a rotor, nozzle, set of blades, or piston, depending on the specific design of the electric generator.

3). Electromagnetic Induction (Step 3)

Electromagnetic induction is the third and final step in the operation of an electric generator.

After heat energy is converted the mechanical energy produced from energy conversion is used to set a moveable component (rotor, nozzle, piston) into motion.

Rotary motion is the type of motion most commonly produced in an electric generator. The moveable component is a conductor, and may occur as a singular solid object, or as a composite that includes a solid core and windings of copper wire which surround it.

In the case of rotors, this copper winding is referred to as the armature.

A magnetic field is usually present in the electric generator. This field may be created by a permanent magnet or stator and field windings, and influences the moveable (rotating) conductor.

The influence of the magnetic field on the moving conductor establishes a potential difference (in voltage and electron-concentration) across the two ends of the conductor, which causes electrons to flow continuously, thereby generating electricity.

Mechanical energy-to-electricity conversion occurs based on the electromagnetic mechanism described above.


On the overall, there are three series of energy conversions that occur in a typical electric generator. These include

  1. Chemical energy-to-Heat energy (step one)
  2. Heat energy-to-Mechanical energy (step two)
  3. Mechanical energy-to-Electricity (step three)



An electric generator is a device which generates electricity by converting chemical, heat and mechanical energy, through combustion, conduction, and electromagnetic induction.

The history of electric generator technology dates back to the eighteenth century, and includes numerous contributions in the fields of electron mobility, electromagnetism, electromechanical dynamics and engineering.

Electromagnetic induction is the working principle of an electric generator. Typically, there are three steps in the operation of generators, which are as follows;

  1. Energy Supply (Step 1)
  2. Energy Conversion (Step 2)
  3. Electromagnetic Induction (Step 3)



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