Electric generator- one of the constituent elements of an autonomous power plant, as well as many others. In fact, it is the most important element, without which the generation of electrical energy is impossible. The generator converts rotational mechanical energy into electrical energy. The principle of its operation is based on the so-called phenomenon of self-induction, when an electromotive force (EMF) arises in a conductor (coil) moving in the magnetic field lines, which can (for a better understanding of the issue) be called electric voltage (although this is not the same ).
The components of an electric generator are a magnetic system (mainly electromagnets are used) and a system of conductors (coils). The first creates a magnetic field, and the second, rotating in it, converts it into an electric one. Additionally, the generator also has a voltage removal system (collector and brushes, connecting the coils in a certain way). It actually connects the generator with consumers of electric current.
You can get electricity yourself, having carried out the simplest experiment. To do this, you need to take two magnets of different poles or turn two magnets with different poles to each other, and place a metal conductor between them in the form of a frame. Connect a small (low power) light bulb to its ends. If the frame starts to rotate in one direction or another, the light bulb will start to glow, that is, an electrical voltage has appeared at the ends of the frame, and an electric current has flowed through its spiral. The same thing happens in an electric generator, the only difference is that in an electric generator there is a more complex system of electromagnets and a much more complicated coil of conductors, usually copper.
Electric generators differ both in the type of drive and in the type of output voltage. By the type of drive that sets it in motion:
- Turbine generator - driven by a steam turbine or gas turbine engine. Mainly used in large (industrial) power plants.
- Hydrogenerator - driven by a hydraulic turbine. It is also used in large power plants operating by the movement of river and sea water.
- Wind turbine - powered by wind energy. It is used both in small (private) wind farms and in large industrial ones.
- The diesel generator and the gasoline generator are driven by diesel and gasoline engines respectively.
By type of output electric current:
- DC generators - we get direct current at the output.
- AC generators. There are single-phase and three-phase, with single-phase and three-phase output alternating current, respectively.
Different types of generators have their own design features and practically incompatible components. They are united only by the general principle of creating an electromagnetic field by mutual rotation of one system of coils relative to another or relative to permanent magnets. Due to these features, only qualified specialists can repair generators or their individual components.
D.C (direct current) –it is the ordered movement of charged particles in one direction. In other words
quantities characterizing electric current, such as voltage or current, are constant both in value and in direction.
In a direct current source, such as a regular finger-type battery, electrons move from minus to plus. But historically, the direction from plus to minus is considered to be the technical direction of the current.
For direct current, all the basic laws of electrical engineering apply, such as Ohm's law and Kirchhoff's laws.
Story
Initially, direct current was called - galvanic current, since it was first obtained using a galvanic reaction. Then, at the end of the nineteenth century, Thomas Edison made attempts to organize the transmission of direct current through power lines. At the same time, the so-called "war of currents", in which there was a choice as the main current between alternating and direct. Unfortunately, direct current “lost” this “war” because, unlike alternating current, direct current suffers large losses in power when transmitted over distances. Alternating current is easy to transform and therefore transmit over long distances.
DC sources
DC sources can be batteries, or other sources in which current appears due to a chemical reaction (for example, a finger battery).
Also, DC sources can be a DC generator, in which the current is generated due to
phenomenon of electromagnetic induction, and then rectified by means of a collector.
Direct current can be obtained by rectifying alternating current. For this, there are various rectifiers and converters.
Application
Direct current is widely used in electrical circuits and devices. For example, at home, most appliances, such as a modem or mobile charger, operate on direct current. The car's alternator generates and converts direct current to charge the battery. Any portable device is powered by a DC source.
In industry, DC is used in DC machines such as motors or generators. In some countries there are high voltage DC power lines.
Direct current has also found its use in medicine, for example in electrophoresis, a treatment procedure using electric current.
In railway transport, in addition to alternating current, direct current is also used. This is due to the fact that traction motors, which have more rigid mechanical characteristics than
Ten times a day, turning on and off the light and using household appliances, we do not even think about where the electricity comes from and what its nature is. It is clear, of course, that according to power lines ( power line) it comes from the nearest power plant, but this is a very limited idea of \u200b\u200bthe world around us. But if electricity generation around the world stops for at least a couple of days, the death toll will be measured in hundreds of millions.
How is current generated?
From the physics course we know that:
- All matter is made up of atoms, the smallest particles.
- Electrons revolve in an orbit around the nucleus of an atom, they have a negative charge.
- The nucleus contains positively charged protons.
- Normally, this system is in a state of equilibrium.
But if at least one atom loses only one electron:
- Its charge becomes positive.
- A positively charged atom will begin to attract an electron towards itself, due to the difference in charges.
- To get the missing electron for yourself, it will have to be "plucked" from someone's orbit.
- As a result, one more atom will become positively charged and everything will be repeated, starting from the first point.
- Such cyclicity will lead to the formation of an electrical circuit and the linear distribution of current.
So from the point of view of nuclear physics, everything is extremely simple, the atom is trying to get what it lacks the most, and thus starts the reaction .
The "golden age" of electricity
Man adapted the laws of the universe to his needs relatively recently. And it happened about two centuries ago, when an inventor named Volt developed the first battery capable of maintaining a charge of sufficient power for a long time.
Attempts to use the current for their own benefit have an ancient history. Archaeological excavations have shown that even in Roman sanctuaries, and then in the first Christian churches, there were handicraft "batteries" made of copper, which gave minimal voltage. Such a system was connected to the altar or its enclosure, and as soon as the believer touched the structure, he immediately received “ divine spark". Rather, this is the invention of one craftsman than widespread practice, but the fact is curious, in any case.
The twentieth century has become power boom:
- Not only new types of generators and batteries appeared, but also unique concepts for the production of this very energy were developed.
- For several decades, electrical appliances have tightly entered the life of every person on the planet.
- There are no countries left, except for the least developed ones, where power plants and held power lines.
- All further progress was based on the possibilities of electricity and the devices that work from it.
- The era of computerization has made a person addicted to current, in the truest sense of the word.
How to get electricity?
To imagine a person as a drug addict who regularly needs a “life-giving dose of electricity” is a little naive, but try to completely de-energize your home and live in peace for at least a day. Despair can make you remember the original ways of extracting current. In practice, this is of little use to anyone, but maybe a couple of Volts will save a life or help impress a child:
- Dead battery phone can be rubbed on clothes, jeans or a woolen sweater will do. Static electricity won't last long, but it's at least something.
- If there is nearby sea water, you can pour it into two jars or glasses, connect them with a copper wire, after wrapping both ends of it with foil. Of course, for all this, in addition to salt water, you will also need containers, copper and foil. Not the best option for extreme situations.
- Much more realistic iron nail and a small brass instrument. Two pieces of metal should be used as the anode and cathode - a nail in the nearest tree, copper in the ground. Pull any thread between them, a simple design will give about one Volt.
- If use precious metals- gold and silver, it will be possible to achieve greater tension.
How to save electricity?
There can be various reasons for saving electricity - a desire to save the environment, an attempt to reduce monthly bills, or something else. But the methods are always about the same:
It is not always necessary to severely limit yourself in something in order to reduce costs. There is another good tip - unplug all appliances while you are not using them.
The refrigerator, of course, does not count. Even being in "standby" mode, the equipment consumes a certain amount of electricity. But if you think even for a second, you can come to the conclusion that you don’t need almost all the devices for most of the day. And all this time they keep burning your electricity .
Modern technologies are also aimed at reducing the overall level of electricity consumption. What are at least worth energy saving light bulbs, which can reduce the cost of lighting a room, five times as much. The advice to live by "sundial" may seem wild and absurd, but it has long been proven that artificial lighting increases the risk of depression.
How is electricity generated?
Going into the scientific details:
- The current appears due to the loss of an electron by an atom.
- A positively charged atom attracts negatively charged particles to itself.
- Another atom loses its electrons from orbit and history repeats itself.
- This explains the directed movement of the current and the presence of a propagation vector.
But in general electricity is generated by power plants. They either burn fuel, or use the energy of splitting atoms, or maybe even use natural elements. We are talking about solar panels, windmills and power plants.
The resulting mechanical or thermal energy, due to the generator, is converted into a current. It accumulates in batteries and enters every house through power lines.
Today, it is not necessary to know where electricity comes from in order to enjoy all the benefits that it provides. People have long moved away from the original essence of things and slowly begin to forget about it.
Video: where does electricity come from?
This video will clearly show the path of electricity from the power plant to us, where it comes from and how it enters our house:
Current generator converts mechanical (kinetic) energy into electrical energy. In the energy sector, only rotating electric machine generators are used, based on the occurrence of an electromotive force (EMF) in a conductor, which is somehow affected by a changing magnetic field. That part of the generator, which is designed to create a magnetic field, is called an inductor, and the part in which the EMF is induced is called an armature.
The rotating part of the machine is called rotor, and the fixed part stator. In AC synchronous machines, the inductor is usually the rotor, and in DC machines, the stator. In both cases, the inductor is usually a two- or multi-pole electromagnetic system equipped with an excitation winding fed by direct current (excitation current), but there are also inductors consisting of a system of permanent magnets. In induction (asynchronous) alternators the inductor and armature cannot be clearly (structurally) distinguished from each other (we can say that the stator and rotor are both an inductor and an armature at the same time).
More than 95% of the electricity in the world's power plants is produced using synchronous alternators. With the help of a rotating inductor in these generators, a rotating magnetic field is created, which induces an alternating EMF in the stator (usually three-phase) winding, the frequency of which exactly corresponds to the rotor speed (is in synchronism with the inductor speed). If the inductor, for example, has two poles and rotates at a frequency of 3000 r/min (50 r/s), then a variable EMF with a frequency of 50 Hz is induced in each phase of the stator winding. The design of such a generator is simplistically shown in Fig. 1.
Rice. 1. The principle of the device of a two-pole synchronous generator. 1 stator (armature), 2 rotor (inductor), 3 shaft, 4 housing. U-X, V-Y, W-Z - parts of the windings of three phases placed in the stator grooves
The stator magnetic system is a compressed package of thin steel sheets, in the grooves of which the stator winding is located. The winding consists of three phases, shifted in the case of a two-pole machine relative to each other by 1/3 of the stator perimeter; in the phase windings, therefore, EMFs are induced, shifted relative to each other by 120o. The winding of each phase, in turn, consists of multi-turn coils connected to each other in series or in parallel. One of the simplest design options for such a three-phase winding of a two-pole generator is simplified in Fig. 2 (usually the number of coils in each phase is more than shown in this figure). Those parts of the coils that are outside the grooves, on the frontal surface of the stator, are called frontal connections.
Rice. 2. The simplest principle of the device of the stator winding of a three-phase two-pole synchronous generator in the case of two coils in each phase. 1 surface scan of the stator magnetic system, 2 winding coils, U, V, W phase windings start, X, Y, Z phase winding ends
The poles of the inductor and, in accordance with this, the pole divisions of the stator, there may be more than two. The slower the rotor rotates, the greater the number of poles should be at a given current frequency. If, for example, the rotor rotates at a frequency of 300 r / min, then the number of poles of the generator, to obtain an alternating current frequency of 50 Hz, should be 20. For example, at one of the largest hydroelectric power plants in the world, Itaipu HPP (see Fig. 4) generators operating at 50 Hz are 66-pole, and generators operating at 60 Hz are 78-pole.
The excitation winding of a two- or four-pole generator is placed as shown in fig. 1, in the grooves of the massive steel core of the rotor. Such a rotor design is necessary in the case of high-speed generators operating at a speed of 3000 or 1500 r / min (especially for turbogenerators designed to be connected to steam turbines), since at this speed large centrifugal forces act on the rotor winding. With a larger number of poles, each pole has a separate excitation winding (Fig. 3.12.3). Such a salient pole principle of the device is used, in particular, in the case of low-speed generators intended for connection with hydraulic turbines (hydraulic generators), usually operating at a speed of 60 r/min to 600 r/min.
Very often, such generators, in accordance with the design of powerful hydraulic turbines, are made with a vertical shaft.
Rice. 3. The principle of the rotor of a low-speed synchronous generator. 1 pole, 2 field winding, 3 mounting wheel, 4 shaft
Excitation winding synchronous generator usually powered by direct current from an external source through slip rings on the rotor shaft. Previously, a special DC generator (exciter) was provided for this, rigidly connected to the generator shaft, and now simpler and cheaper semiconductor rectifiers are used. There are also excitation systems built into the rotor, in which the EMF is induced by the stator winding. If permanent magnets are used to create a magnetic field instead of an electromagnetic system, then the excitation current source is eliminated and the generator becomes much simpler and more reliable, but at the same time more expensive. Therefore, permanent magnets are usually used in relatively low-power generators (up to several hundred kilowatts).
The design of turbogenerators, due to the relatively small diameter cylindrical rotor, is very compact. Their specific gravity is usually 0.5…1 kg/kW and their power rating can be up to 1600 MW. The device of hydrogenerators is somewhat more complicated, the diameter of the rotor is large and their specific gravity is therefore usually 3.5 ... 6 kg / kW. Until now, they have been manufactured with a nominal power of up to 800 MW.
During the operation of the generator, energy losses occur in it caused by the active resistance of the windings (losses in copper), eddy currents and hysteresis in the active parts of the magnetic system (losses in steel) and friction in the bearings of rotating parts (friction losses). Despite the fact that the total losses usually do not exceed 1 ... 2% of the generator power, the removal of heat released as a result of losses can be difficult. If we simply assume that the mass of the generator is proportional to its power, then its linear dimensions are proportional to the cube root of the power, and the surface dimensions are proportional to the power to the power of 2/3. With increasing power, therefore, the heat sink surface grows more slowly than the rated power of the generator. While natural cooling is sufficient for powers of the order of several hundred kilowatts, at higher powers it is necessary to switch to forced ventilation and, starting from approximately 100 MW, use hydrogen instead of air. For even higher powers (for example, more than 500 MW), it is necessary to supplement hydrogen cooling with water. In large generators, it is necessary to specially cool the bearings, usually using oil circulation for this.
Generator heat dissipation can be significantly reduced by using superconducting excitation windings. The first such generator (with a capacity of 4 MVA), designed for use on ships, was manufactured in 2005 by the German electrical engineering company Siemens (Siemens AG) . The rated voltage of synchronous generators, depending on the power, is usually in the range from 400 V to 24 kV. Higher rated voltages (up to 150 kV) were also used, but extremely rarely. In addition to synchronous mains frequency generators (50 Hz or 60 Hz), high-frequency generators (up to 30 kHz) and low-frequency generators (16.67 Hz or 25 Hz) are also produced, which are used on electrified railways in some European countries. Synchronous generators also include, in principle, a synchronous compensator, which is a synchronous motor that operates at idle and delivers reactive power to the high-voltage distribution network. With the help of such a machine, it is possible to cover the reactive power consumption of local industrial power consumers and free the main grid of the power system from reactive power transmission.
In addition to synchronous generators, relatively rarely and at relatively low powers (up to several megawatts), they can also be used asynchronous generators. In the rotor winding of such a generator, the current is induced by the stator magnetic field if the rotor rotates faster than the mains frequency stator rotating magnetic field. The need for such generators usually arises when it is impossible to ensure a constant speed of rotation of the primary engine (for example, a wind turbine, some small hydro turbines, etc.).
At DC generator the magnetic poles, together with the excitation winding, are usually located in the stator, and the armature winding is located in the rotor. Since a variable EMF is induced in the rotor winding during its rotation, the armature must be supplied with a collector (switch), with the help of which a constant EMF is obtained at the generator output (on the collector brushes). Currently, direct current generators are rarely used, since direct current is easier to obtain using semiconductor rectifiers.
Electrical generators include electrostatic generators, on the rotating part of which a high voltage electric charge is created by friction (triboelectrically). The first such generator (a hand-rotated sulfur ball, which was electrified by friction against a person’s hand) was made in 1663 by the mayor of the city of Magdeburg (Magdeburg, Germany) Otto von Guericke (Otto von Guericke, 1602–1686). In the course of their development, such generators made it possible to discover many electrical phenomena and patterns. Even now they have not lost their significance as a means of conducting experimental research in physics.
The first one was made on November 4, 1831 by Michael Faraday, a professor at the Royal Institution in London (1791-1867). The generator consisted of a horseshoe-shaped permanent magnet and a copper disk rotating between magnetic poles (Fig. 3.12.4). When the disk rotated between its axis and the edge, a constant EMF was induced. By the same principle, more advanced unipolar generators are arranged, which are used (although relatively rarely) at the present time.
Rice. 4. The principle of the device unipolar generator Michael Faraday. 1 magnet, 2 rotating copper disk, 3 brushes. Disc handle not shown
Michael Faraday was born into a poor family and after elementary school, at the age of 13, he became an apprentice bookbinder. From books, he independently continued his education, and from the British Encyclopedia he got acquainted with electricity, made an electrostatic generator and a Leyden jar. To expand his knowledge, he began attending public lectures on chemistry by the director of the Royal Institute, Humphrey Davy (1778-1829), and in 1813 received the position of his assistant. In 1821 he became the chief inspector of this institute, in 1824 a member of the Royal Society (Royal Society) and in 1827 professor of chemistry at the Royal Institute. In 1821, he began his famous experiments on electricity, during which he proposed the principle of operation of an electric motor, discovered the phenomenon of electromagnetic induction, the principle of a magnetoelectric generator, the laws of electrolysis, and many other fundamental physical phenomena. A year after Faraday's experience described above, on September 3, 1832, the Parisian mechanic Hippolyte Pixii (Hippolyte Pixii, 1808–1835) manufactured by order and under the guidance of the founder of electrodynamics Andre Marie Ampere (Andre Marie Ampere, 1775–1836) a generator with a manually rotated Faraday, a magnet (Fig. 5). An alternating EMF is induced in the armature winding of the Pixie generator. To rectify the resulting current, an open mercury switch was first attached to the generator, switching the polarity of the EMF with each half-turn of the rotor, but it was soon replaced by a simpler and safer cylindrical brush collector, shown in Fig. 5.
Rice. 5. The principle of the device magnetoelectric generator Hippolyta Pixie (a), plot of the induced EMF (b) and plot of the pulsating constant EMF obtained using the collector (c). Handle and bevel gear not shown
A generator built on the Pixie principle was first used in 1842 at his plant in Birmingham (Birmingham) to power galvanic baths by the English industrialist John Stephen Woolrich (1790–1843), using a 1 hp steam engine as a drive engine. With. The voltage of his generator was 3 V, the rated current was 25 A, and the efficiency was about 10%. The same, but more powerful generators quickly began to be introduced at other electroplating enterprises in Europe. In 1851, the German military doctor Wilhelm Josef Sinsteden (Wilhelm Josef Sinsteden, 1803–1891) proposed using electromagnets instead of permanent magnets in the inductor and feeding them with current from a smaller auxiliary generator; he also discovered that the efficiency of the generator will increase if the steel core of the electromagnet is made not from massive, but from parallel wires. However, the ideas of Sinsteden began to be really used only in 1863 by the self-taught English electrical engineer Henry Wilde (Henry Wilde, 1833–1919), who proposed, among other innovations, to put an exciter machine (English exitatrice) on the generator shaft. In 1865, he made a generator of hitherto unprecedented power of 1 kW, with which he could even demonstrate the melting and welding of metals.
The most important improvement DC generators became their self-excitation, the principle of which was patented in 1854 by the chief engineer of the Danish state railways, Soren Hjorth (Soren Hjorth, 1801–1870), but did not find practical application at that time. In 1866, this principle was again discovered independently by several electrical engineers, including the already mentioned G. Wilde, but it became widely known in December 1866, when the German industrialist Ernst Werner von Siemens (Ernst Werner von Siemens, 1816–1892) applied it in his compact and highly efficient generator. On January 17, 1867, his famous report on the dynamoelectric principle (on self-excitation) was read at the Berlin Academy of Sciences. self-excitation made it possible to abandon auxiliary excitation generators (from exciters), which made it possible to generate much cheaper electricity in large quantities. For this reason, the year 1866 is often considered the birth year of high current electrical engineering. In the first self-excited generators, the excitation winding was switched on, like that of Siemens, in series (in series) with the armature winding, but in February 1867, the English electrical engineer Charles Wheatstone (Charles Wheatstone, 1802–1875) proposed parallel excitation, which made it possible to better regulate the EMF of the generator to which it came even before the reports of serial excitation discovered by Siemens (Fig. 6).
Rice. 6. Development of excitation systems for DC generators. a permanent magnet excitation (1831), b external excitation (1851), c series self-excitation (1866), d parallel self-excitation (1867). 1 armature, 2 excitation winding. Excitation current adjusting rheostats not shown
Need for alternators originated in 1876, when the Russian electrical engineer Pavel Yablochkov (1847–1894), working in Paris, began to illuminate city streets with the help of alternating current arc lamps (Yablochkov candles) he manufactured. The first generators needed for this were created by the Parisian inventor and industrialist Zenobe Theophile Gramme (1826–1901). With the start of mass production of incandescent lamps in 1879, alternating current lost its importance for some time, but gained relevance again due to the increase in the range of electricity transmission in the mid-1880s. In 1888-1890, the owner of his own research laboratory Tesla-Electric (Tesla-Electric Co., New York, USA), the Serbian electrical engineer Nikola Tesla (Nikola Tesla, 1856-1943) who emigrated to the United States and the chief engineer of the AEG company (AEG, Allgemeine Elektricitats-Gesellschaft) Russian electrical engineer Mikhail Dolivo-Dobrovolsky (1862–1919) who emigrated to Germany developed a three-phase alternating current system. As a result, the production of ever more powerful synchronous generators for the constructed thermal and hydroelectric power plants.
An important stage in the development of turbogenerators can be considered the development in 1898 of a cylindrical rotor by the co-owner of the Swiss electrical plant Brown, Boveri and Company (Brown, Boveri & Cie., BBC) Charles Eugen Lancelot Brown (Charles Eugen Lancelot Brown, 1863–1924). The first generator with hydrogen cooling (capacity 25 MW) was released in 1937 by the American company General Electric (General Electric), and with in-line water cooling - in 1956 by the British company Metropolitan Vickers.
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