An electric generator is a device designed to produce electricity from other types of energy. The most common is the one that transforms mechanical energy into electrical power. Sometimes it is also called a generator set.
An electric generator is an instrument that converts mechanical energy into electrical energy. The operating principle is based on the principle of electromagnetic induction.
Michael Faraday devised the first electromagnetic generator: the Faraday disk. Faraday's disk showed that electricity could be generated using magnetism. Faraday's Law states that the induced voltage in a circuit is directly proportional to the change in magnetic flux in a conductor or coil.
For what is used an electric generator?
The electric generators can be used for:
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Generate electricity in order to transmit and distribute it over power lines to domestic.
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As an emergency backup power or to generate electricity permanently. They work as standby generators.
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Supply the electrical power required for automobiles, ships, trains, or aircraft.
How does an electric generator work?
The electric generators used in power plants are pretty complex, but their operating principle is straightforward:
Schematically they consist of one or more conductive wire windings (coils). These coils are supplied with mechanical energy to rotate them within an intense magnetic field.
Mechanical energy can be supplied by a turbine. The coil, free to rotate, is called a rotor, while the fixed magnet is called a stator. There are three types of turbines:
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The water turbine, used in hydroelectric plants.
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The steam turbine: used in solar thermal plants, nuclear power plants, and coal plants.
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The gas turbine, used in combined cycle power plants using natural gas or even wind turbines.
In some hydroelectric power plants, the generator can work in reverse. In this way, it works like a water pump. When there is a surplus of energy, transfer switches, and it starts pumping water.
Why is an electric generator similar to an electric motor?
What happens in an electric current generator is the exact opposite of what happens in an electric motor.
In an electric motor, the force exerted by the magnet on the current-covered circuit is translated into a couple of forces. This pair of forces impart a rotary motion to the rotor.
In the case of the electric generator, no current flows to the circuit. Instead, rotation is imparted through some form of mechanical energy.
Example to describe the electrical generator operation
Imagine that we have a simple coil that consists of a square coil to understand the operating system. The rotary movement of the loop concerning the field generates the phenomenon of electromagnetic induction. It generates a current in the loop.
The intensity of the current, like the intensity of the induced emf, will be proportional to the flux of the magnetic field:
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When the loop is perpendicular to the magnetic field, the power of the induced current will be maximum;
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The induced current decreases as the coil rotate to positions more oblique than the magnetic field lines of force. When the coil is parallel to the field, the flow of the field concerning the coil is zero.
The magnetic field will interfere with the electrons in the conductor to induce a flow of electric current inside it.
By continuing to rotate the loop, the direction of the current is reversed. As a result, the current strength increases as the loop returns to offer a greater surface area of the field force lines. Until it reaches a new maximum value.
This maximum is the same as the previous one but with an opposite sign. It continues to decrease as the rotation of the loop continues.
The current produced by such a generator, therefore, does not have a constant intensity. Instead, however, it follows a sinusoidal trend: such a current is called alternating current.
Typically, the coils of an alternator are connected to form three AC generators out of phase with each other. Thus, the alternator is said to produce a three-phase current, which is supplied in our homes.
The transformer is an instrument capable of transforming an alternating current with a specific effective voltage to a different voltage. The transformation happens with small energy losses.
What are the different types of electric generators?
If we want to buy an electric generator, we must first know what types there are and what characteristics they have:
Portable generators or stationary power generator
Stationary generators are generally placed in particular rooms. They are used regularly or kept ready at any time to start operating. Sometimes they work autonomously in the event of a power outage.
Laptops range from the smallest and lightest leisure generators to giant truck-mounted generators.
Type of the engine used.
The generators are also classified according to the fuel they use and, therefore, according to the type of engine that equips them:
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2-stroke generator
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4-stroke gasoline generator
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diesel electric generator
The gasoline electric generator is more popular than the diesel generator.
The 2-stroke generator is the smallest and most compact. Moreover, it is the one with the most straightforward engine. That makes it to be a good option for portable generators.
The 4-stroke only works with gasoline. Thus, it also produces less greenhouse gas emissions. However, it also has more significant power cuts: power increases with the available range of 4-stroke models and even more with diesel generators.
In the 4-stroke sector, some run on gas (LPG, butane, propane) that emits less gas.
Inverter power generator
Another important difference between the various generators is the control electronics they have on board. The simplest models provide 12V in direct current and 220V in alternating current.
However, the current supplied suffers from fluctuations in emissions depending on the instantaneous absorption of the applied load.
Power inverters are capable of supplying a very stable and regular current.
Output voltage
Depending on the needs, there is the possibility of having single-phase (230V output) or three-phase (400V) current generators.
However, it should be noted that there is also a DC or 12V generator. This generator is generally combined with the standard 230V AC supply.
The use of electromagnets rather than permanent magnets greatly increased the power output of a dynamo and enabled high power generation for the first time.
Electric start current generator
Most portable UPSs start with a manual pull-out system. Others have integrated a starter motor and battery to operate it. Naturally, it implies an increase in the weight and dimensions of the entire device. However, it has undeniable advantages if frequent starts are necessary.
In addition, an evolution of the models with a starter motor are those that have an automatic starter. This evolution is due to an electronic section for control and interfaces with the house's electrical network.
For example, when there is no energy, the system detects the voltage drop and automatically starts the generator. Thus, it keeps the house under an electrical load.
Silenced Power Generator
A final category is that of generators designed to emit as little noise as possible.
The silent power generator is sought when designed to work in the areas where people stay and work.
The machine is equipped with soundproofing systems and reduction of vibrations emitted. The reduction in perceived noise is noticeable. When approaching the purchase of one of these generators, the noise level in decibels expressed in the technical manual should be verified.
Generators that are not powered by mechanical energy
There are several electric generators that the input source is not mechanical energy.
Among this type of generators, we find:
Photovoltaic generators
Photovoltaic generators use photovoltaic solar panels. Each solar panel is made up of an arrangement of photovoltaic cells. Photovoltaic cells are responsible for generating electricity thanks to the photovoltaic effect.
Electrochemical generators
When the flow of electrons is produced by an oxidation-reduction reaction, there is an electrochemical generator. The most common are batteries and fuel cells.
Radioisotope generators
Generation in the radioisotope thermoelectric generator is based on the decomposition of radioactive isotopes. Radioactive decomposition produces emission of particles and heat. Electricity production can be obtained directly from the displacement of electrically charged particles or indirectly from the heat produced.
Differential thermal generators
Electricity production is obtained from a temperature difference for the Seebeck effect. This system can work with any thermal gradient.