Electric generator
An electrical generator ( to Latin generare, bring forth ',' create ' ) is an electrical machine that converts kinetic energy or mechanical energy into electrical energy and thus technically the equivalent of an electric motor, which converts reversed electrical energy into kinetic energy.
The generator is based on the 1831 discovered by Michael Faraday principle of electromagnetic induction.
- 3.1 First generation by induction
- 3.2 First large-scale use of alternators
- 3.3 First generators without permanent magnets
- 3.4 First polyphase alternating current generators
- 3.5 First industrial-scale power plants
Operation
All generators that operate by means of electrical induction, the principle is common to convert mechanical power into electrical power. The mechanical power supplied to the generator in the form of the rotation of a mechanical shaft. The conversion is based on the Lorentz force acting on moving electrical charges in a magnetic field. Moves a conductor transverse ( perpendicular ) to the magnetic field, the Lorentz force acts on the charges in the conductor in the direction of this conductor and sets them in motion so. This charge transfer results in a potential difference and producing an electrical voltage between the ends of the conductor. The adjacent animation, the displacement of the conductor ( or the relevant two coil sections ) is only relevant cross perpendicular to the magnetic field. This is illustrated by means of the red area. The greater the change in area per unit time ( due to distance traveled of the conductor ), the higher the voltage. To increase the voltage, a plurality of conductors connected in the form of a coil connected in series are used.
This mode of action is distinct from that of electrostatic generators, in which the separation of electric charges by the electric field, the non- magnetic, is made.
Inside the generator, the rotor (also called a rotor ) rotating (also called stand) against the fixed stator housing. By the rotor with a permanent magnet or an electromagnet ( or the field coil excitation winding called ) generated rotating DC magnetic field is induced in the conductors or conductor windings of the stator voltage by the Lorentz force.
DC generators in the current in the rotor ( rotor) is induced, the field coil or the permanent magnet is outside. The generated current is rectified by a commutator.
The generated electric power is equal to the mechanical power minus the losses occurring. This follows the power equation of an electric generator:
Is the electric power generated is supplied to the mechanical power, the power loss. In the generator itself, there are so-called copper losses and iron losses, which still must also be deducted.
The discharged voltage can be controlled by the magnitude of the excitation field, if this is generated by an electromagnet ( electrical energization, external excitation ). This control method is used, not only in plants but also in light of machinery, vehicle ( alternator regulator ).
Construction
Rotation generator
To produce a sinusoidal voltage in the alternating current or three-phase synchronous generator, the rotor has to generate a homogeneous magnetic field as possible. He has observed, in addition to the field coil pole pieces with mushroom-shaped cross-section, which distribute the magnetic field. The number of poles (at least two, more even- numbers possible ) decide on the frequency of the voltage supplied at a given speed. The field winding has to be very well secured so that they can withstand the high centrifugal forces. An operating condition to be avoided is the load shedding that would destroy the generator without the intervention of a controller, because the rise speed of the driving steam or gas turbine, leads to excessive centrifugal forces in the armature windings. The rotor with squirrel-cage induction or asynchronous generators requires no power supply, the case of synchronous generators, the power was supplied through slip rings takes place. By auxiliary generators on the same shaft can be dispensed with synchronous generators on the slip rings.
The generator windings are distributed internally housed in several slots of the hollow cylindrical stator package. The filled with the windings grooves narrowing again towards the inside and also form the pole pieces. The outer shell of the core stack contains no windings, it serves as a yoke or a magnetic yoke to concentrate the alternating magnetic field in the windings.
DC generators require a commutator ( commutator ) for acceptance and rectification of the generated with them in the rotor voltage. As with them all the generated electrical power must be transmitted via the commutator, today they are no longer in use. Requires one DC voltage, AC generators are used for downstream rectifiers, such as the generator in the vehicle ( colloquially alternator).
Asynchronous generators are constructed as well as induction motors. You do not have a field coil still slip rings, but a squirrel-cage rotor. The rotating magnetic field generated by this current in the alternator windings. Asynchronous generators can supply electricity so only if they are connected to an AC voltage or already generate electricity. In isolated operation, they are burdened with this, capacitors and have for launching frequently a small permanent magnet in the rotor. But often enough the residual magnetization.
Almost all modern generators are three-phase asynchronous lower power, while large generators (from about 0.1 MW ), but also the generator in the motor vehicle and the bicycle are synchronous machines. Synchronous machines are only able to provide in addition to the real power controlled, the reactive power required in plants are available.
Linear generator
A linear generator (also called induction generator or shaking ) in its simplest form, be realized with the engine Stelzer. In this case, located on both sides of the free swinging piston each have a coil into which the end of the piston is immersed, on which a magnet is located. The frequency of the alternating voltage generated depends on the frequency of the free swinging piston, and varies depending on the load.
A special application example of this technique are the shaking flashlights. Here, a strong neodymium magnet moves through the shaking through a coil. The voltage thus generated is sufficient to load a double-layer capacitor ( 1-2 Farad, 3-4 volts), which then provide one or more LED bulbs for long periods with the current can. Another application example for linear generators are therefore equipped batteries (eg AA or AAA size), which can be used universally for similarly efficient appliances.
Large-scale generators
Large-scale three-phase synchronous machines, most of which are designed as revolving field, consist of a stator said fixed part, which is a large induction coil with an iron core in principle. The stator is usually not a massive iron body, but is set up to avoid eddy currents of many individual, mutually insulated laminations. For large generators of these fins are made from non-grain dynamo sheet, more rarely, of grain-oriented dynamo sheet. The rotating part of the generator consists of the camps and the forged and massive full drum rotor ( cylindrical rotor ). In the rotor occur in symmetrical load to no eddy currents, and therefore can be dispensed with lamination. The rotor is supplied via the shaft mechanical power. The large generators used today for power plants are almost invariably Vollpolmaschinen for a (specific ) line frequency of 50 or 60 Hz
High-speed synchronous generators, as they are used in combination with steam turbines in power plants are referred to as turbo generator or Vollpolmaschine. Its excitation field typically has two or four poles. The power of the excitation winding is carried out in modern facilities according to the principle of brushless or static excitation. For hydro, due to the low rotational speed of the turbine salient typically come with much more than four poles for use.
The advantage of synchronous generators compared to asynchronous is that they can deliver depending on the control of both active power and inductive or capacitive reactive power to the grid, or to record from him. Depending on the amount of their magnetic excitation synchronous generators give real power from or supply additional reactive power into the grid, which is needed to compensate for inductive and capacitive loads. It allows you to serve in electric power systems as an active phase shifter. Asynchronous not have a generator in the electrical industry this meaning.
The strand coils of large generators heat up considerably during operation and need to be cooled. The coils in the stator to be cooled with water, which gives off its heat in a heat exchanger downstream in the rotor, however, with hydrogen, is circulated through the generator housing at a pressure up to 10 bar. With hydrogen ( specific heat capacity = 14.3 J / ( gK ) ) is achieved significantly better cooling with less friction than with air (only 1 J / ( gK ) ). Generators with a power of less than 300 MVA are usually cooled with air. The air circulating in the housing and through the coils in the stator. The fans are mounted directly on the rotor. The air is cooled with water coolers, which are situated in the lower part of the generator housing.
A special feature are the generators for the generation of traction power dar. Because of the single-phase voltage at approximately 16.7 Hz, these generators are designed as AC synchronous machine and rotate at a speed of 1000 revolutions per minute ( 1/3 the speed of 50 Hz generators). Their frequency was formerly at 50 Hz / 3 = 162/3 Hz and was later changed due to technical reasons. The magnetic flux within these generators is opposite the river in 50 -Hz machines with the same performance three times as large. Therefore traction power generators required correspondingly larger cross-sections of iron. They are significantly larger than comparable 50 Hz machines for this reason. There is also a double mains frequency rotating and pulsating torque on the drive. This pulsation also has an impact on the foundations of the machine; the generator is therefore placed on springs. Between the drive and generator, an elastic coupling is connected in the same reason. Traction power generators are usually powered by electric motors from the power grid (the combination is called converters ), the establishment is called substation. Today, traction power is electronically generated by the mains voltage in substations.
In Mülheim Siemens plant the world's largest three-phase synchronous generator for the Finnish Olkiluoto nuclear power plant was manufactured. It has a rated apparent power of 1992 MVA.
Steam engine -driven, 56 - pole generator with six-pole exciter ( Year: 1910; 650 kW)
Generator in the power plant Schwarze Pumpe ( Year: 1995, 1000 MVA)
Turbogenerator steam turbine in a nuclear power plant
History
First electricity production by induction
The first known alternator built Hippolyte Pixii at the suggestion of amperes, the model ( see gallery) was made in 1832 of two coils under which revolves a horseshoe magnet. The current is still in the same direction in the machine by means of a commutator. In the same year of Michael Faraday built a Unipolarmaschine which generates a direct current on rotation of the cylindrical permanent magnet on the axis of rotation through unipolar induction. Also in 1832, a vibrating apparatus was constructed for the production of Dal Negro; other non-rotating power generators were built by Carl Friedrich Gauss and others.
First large-scale use of alternators
The alternator of the Company Alliance ( see gallery) after excitation by Floris Nollet ( Brussels) from 1849 was the first generator, which found significant use in industry. The intended purpose of the machine was to decompose water electrochemically to obtain coal gas for lighting. In fact, however, most machines were used without commutator in English and French lighthouses for the operation of arc lamps. The last ones were only taken in the turn of the 20th century out of service.
First generators without permanent magnets
As the inventor of the generator without permanent magnets is preferred Werner von Siemens called, which the dynamo-electric principle discovered in 1866 and a first dynamo endowed with it. Prior to Siemens, however Ányos Jedlik 1851, Søren Hjorth had in 1854 with the power generated by the machine itself fed the field magnets and described this. At the same time discovered with Siemens and also published Samuel Alfred Varley and Charles Wheatstone this principle, with the variant of the Wheatstone a large scale proved to be the more important later.
First multi-phase alternators
Within the framework of the Frankfurt International Electrotechnical Exhibition of 1891 AC machines in operation that were built specifically for the production of multi-phase alternating current. The first of these generators Friedrich August Haselwander had already been built in 1887. This has already produced three-phase alternating current. The American Charles Bradley acquired at the beginning in 1897 a patent for a two-phase alternator. Furthermore, it was an alternator of the company Schuckert and a generator of Brown, Boveri & Cie. (see gallery ) is presented. The first two phases of power plant in the imperial monarchy was built by Franz Pichler and went in 1892 in the Raabklamm bei Weiz in Styria in operation. This generator was rewound after a few years for three-phase and until operation in 1971.
First industrial-scale power plants
In the following years numerous power plants were built, which derived their energy mostly from hydropower, partly out of steam. In / At Niagara was 1895, the first large-scale power plant in the world connected to the grid, and in 1898 followed by the Kraftübertragungswerke Rheinfelden in Europe as a river power plant. A steam power plant brought the power plant to the grid Budapest in 1895.
Alternator Company Alliance after excitation by Professor Nollet ( Brussels) from 1849
Drawing of an alternator from 1891 by Charles Eugene Lancelot Brown (Brown, Boveri & Cie ).
Contemporary wood engraving of the generator space in the first three-phase power plant in Lauffen that on September 12, 1891 supplied an artificial waterfall and a thousand light bulbs for Electrotechnical Exhibition in Frankfurt. This development of C. E. Brown was still manufactured by Maschinenfabrik Oerlikon.
Steam engines powered two-phase current generator with a ring beam for the power station Budapest 1895