Energy conversion. Ways to convert various types of energy Conversion of energy sources

07.12.2019 childbirth

Send your good work in the knowledge base is simple. Use the form below

Students, graduate students, young scientists who use the knowledge base in their studies and work will be very grateful to you.

Posted on http://www.allbest.ru/

Course work

On the topic: Methods of transformation various kinds energy in energy

Student: Myrza A.

Lecturer: Dzhumartbaeva N.

Kentau-2015

Introduction

1. Ways to convert various types of energies

1.1 Types of electrical energy conversion

1.2 Environmental impact of various energy sources

2. Methods for obtaining electrical energy

2.1 Power plants

Conclusion

List of used literature

Introduction

Energy, from the Greek word energeia, activity or action, is a general measure of various types of movement and interaction. In natural science, the following types of energy are distinguished: mechanical, thermal, electrical, chemical, magnetic, electromagnetic, nuclear, gravitational. Modern science does not exclude the existence of other types of energy. Energy is measured in Joules (J). To measure thermal energy, calories are used, 1 cal = 4.18 J, electrical energy is measured in kW * h = 3.6 * 106 J, mechanical energy is measured in kg * m, 1 kg * m = 9.8 J. Kinetic energy is the result of a change in the state of motion of material bodies. Potential energy- the result of a change in the position of the parts of this system. Mechanical energy is the energy associated with the movement of an object or its position, the ability to perform mechanical work. current alternating voltage

Electricity energy - one of the perfect forms of energy. Its widespread use is due to the following factors: Obtaining large quantities of resources and water sources near the deposit; Possibility of transportation over long distances with relatively small losses; The ability to transform into other types of energy: mechanical, chemical, thermal, light; No pollution environment; The introduction of fundamentally new progressive technological processes based on electricity with a high degree of automation.

V Lately, due to environmental problems, the shortage of fossil fuels and its uneven geographical distribution, it becomes expedient to generate electricity using wind turbines, solar panels, small gas generators. Thermal energy is widely used in modern industries and in everyday life in the form of steam, hot water, fuel combustion products. Ways to convert energy: Mankind has sought from the beginning of its history to master energy in its own interests. Stages of "mastery" of energy: fire, muscular strength of animals, the power of wind, water, steam energy, electric power, nuclear energy. In the Universe, there are processes of energy conversion from one type to another on a huge scale. Humanity is at the very beginning of the path of understanding these processes. The law of conservation of energy - energy is neither created nor destroyed, it passes from one form to another. Distinguish between the energy of ordered motion (free - mechanical, chemical, electrical, electromagnetic, nuclear) and the energy of chaotic motion - heat. At present, there are no methods for directly converting nuclear energy into electrical and mechanical energy; one must first go through the stage of converting energy into thermal energy, and then into mechanical and electrical energy. The conversion of primary energy into secondary energy is carried out at the stations:

· At the thermal power plant TPP - thermal;

· Hydroelectric power stations HPP - mechanical (energy of water movement);

· Hydrostorage station of HPSP - mechanical (energy of movement of water preliminarily filled in an artificial reservoir);

· Nuclear power plant NPP - nuclear (energy of nuclear fuel);

· Tidal power plant PES - tides. In the Republic of Belarus, more than 95% of energy is generated at thermal power plants, which are divided into two types according to their purpose:

1. Condensing thermal power plants of KES are designed to generate only electrical energy;

2. Combined heat and power plants (CHP) where combined production of electric and heat energy is carried out. Methods for obtaining and converting energy. Mechanical energy is converted into heat - by friction, into chemical - by destroying the structure of matter, compression, into electrical - by changing the electromagnetic field of the generator. Thermal energy is converted into chemical, into kinetic energy of motion, and this - into mechanical (turbine), into electrical (thermo emf) Chemical energy can be converted into mechanical (explosion), into thermal (heat of reaction), into electrical (batteries).

1 . Ways to convert various types of energies

1.1 Types of electrical energy conversion

Issues related to the conversion of electrical energy from one of its types to another are dealt with in the field of science and technology, called converter technology (or power electronics). The main types of electrical energy conversion include:

1. AC rectification - converting alternating current (usually industrial frequency) into direct current. This type of conversion has received the greatest development, since some of the consumers of electrical energy can only operate on direct current (electrochemical and electrometallurgical installations, direct current transmission lines, electrolysis baths, rechargeable batteries, radio equipment, etc.), while other consumers have on direct current best performance than on alternating current (regulated electric motors).

2. Inverting current - converting direct current into alternating current. The inverter is used in cases where the energy source generates direct current (DC generators, batteries and other chemical current sources, solar panels, magnetohydrodynamic generators, etc.), and consumers need AC power. In some cases, current inversion is necessary for other types of electrical energy conversion (frequency conversion, phase number conversion).

3. Frequency conversion - conversion of alternating current of one frequency (usually 50 Hz) into alternating current of a different frequency. Such a conversion is necessary to power adjustable AC drives, induction heating and metal melting installations, ultrasonic devices, etc.

4. Conversion of the number of phases. In some cases, there is a need to convert a three-phase current into a single-phase one (for example, to power electric arc furnaces) or, conversely, a single-phase current into a three-phase one. So, on electrified transport, a single-phase alternating current contact network is used, and on electric locomotives, auxiliary machines of three-phase current are used. In industry, three-phase-single-phase frequency converters with direct connection are used, in which, along with the conversion of the industrial frequency to a lower one, the three-phase voltage is also converted into a single-phase one.

3. Converting direct current of one voltage to direct current of another voltage (converting constant voltage). Such a transformation is necessary, for example, on a number of mobile objects, where the source of electricity is a battery or other low-voltage direct current source, and a higher direct voltage is required to power consumers (for example, power supplies for radio engineering or electronic equipment).

There are some other types of electrical energy conversion (for example, the formation of a certain alternating voltage curve), in particular, the formation of powerful current pulses that are used in special installations, adjustable alternating voltage conversion. All types of transformations are carried out using power key elements. The main types of semiconductor switches are diodes, power bipolar transistors, thyristors, gated thyristors, field controlled transistors.

Converters on thyristors are usually divided into two groups: slave and autonomous. In the first, the periodic transition of current from one valve to another (current switching) is carried out under the action of an alternating voltage of some external source. If such a source is an AC network, one speaks of a converter driven by the network. These converters include: rectifiers, network-driven (dependent) inverters, direct frequency converters, phase number converters, AC voltage converters. If the external voltage source providing switching is an AC machine (for example, a synchronous generator or a motor), the converter is called a driven machine.

Autonomous converters perform the functions of shape transformation or voltage (current) regulation by changing the state of controlled power key elements under the action of control signals. Autonomous converters include pulse regulators of direct and alternating voltage, some types of voltage inverters.

Traditionally, power valve converters have been used to obtain a rectified voltage of industrial networks with a frequency of 50 Hz and to obtain an alternating voltage (single-phase or three-phase) when powered from a DC voltage source. For these converters (rectifiers and inverters), diodes and thyristors are used, switched with the mains frequency. The shape of the output voltage and current is determined by the linear part of the circuit and the phase modulation of the control angle.

Rectification and inversion continue to be the leading method of converting electrical energy, however, the conversion methods have undergone significant changes and their varieties have become much more numerous.

The emergence of new types of power semiconductor valves, close to the ideal controllable key element, has significantly changed the approach to the construction of valve converters. Widespread in last years lockable thyristors (GTO - gate turn off thirystor) and insulated gate bipolar transistors (IGBT - insolated gate bipolar transistor) successfully cover the power range up to hundreds and thousands of kilowatts, their dynamic properties are continuously improved, and the cost decreases with increasing output. Therefore, they successfully replaced conventional thyristors with forced switching nodes. The areas of application of pulse voltage converters with new classes of devices have also expanded. Powerful switching regulators are rapidly developing for both stepping up and stepping down the DC supply voltage; pulse converters are often used in energy recovery systems from renewable sources (wind, solar radiation).

Large investments are made in the production of energy using energy-saving technologies, when renewable primary sources are used either to return energy to the grid or to recharge the storage (accumulator) in installations with increased energy supply reliability. There are new classes of converters for electric drives with switched reluctance motors (SRD - switched reluctanse drive). These converters are multi-channel (the number of channels is usually from three to eight) switches that provide serial connection of the motor stator windings with adjustable frequency and voltage. Switching converters are widely used in power supplies for household equipment, chargers, welding machines and a number of new applications (ballasts for lighting installations, electrostatic precipitators, etc.).

In addition to improving the element base of power converter circuits, the strategy for solving circuit problems was greatly influenced by the development of microcontroller devices and digital methods of information processing.

1.2 Impact of various sourceskov energy on the environment

Fuel combustion is not only the main source of energy, but also the most important supplier of pollutants to the environment. Thermal power plants are most "responsible" for the growing greenhouse effect and acid precipitation. They, together with transport, supply the atmosphere with the main share of technogenic carbon (mainly in the form of CO), about 50% of sulfur dioxide, 35% of nitrogen oxides and about 35% of dust. There is evidence that thermal power plants pollute the environment with radioactive substances 2-4 times more than nuclear power plants of the same capacity. TPP emissions contain a significant amount of metals and their compounds. In terms of lethal doses, the annual emissions of a TPP with a capacity of 1 million kW contain more than 100 million doses of aluminum and its compounds, 400 million doses of iron, and 1.5 million doses of magnesium. The lethal effect of these pollutants does not appear only because they enter the body in small quantities. This, however, does not exclude their negative impact through water, soil and other parts of ecosystems. It can be assumed that thermal energy has a negative impact on almost all elements of the environment, as well as on humans, other organisms and their communities. At the same time, the impact of energy on the environment and its inhabitants largely depends on the type of energy carriers (fuel) used. The cleanest fuel is natural gas, followed by oil (fuel oil), coal, brown coal, shale, peat. Although at present a significant share of electricity is produced by relatively clean fuels (gas, oil), however, the trend towards a decrease in their share is natural. According to available forecasts, these energy carriers will lose their leading role already in the first quarter of the 21st century. Here it is appropriate to recall the statement of D.I. Mendeleev on the inadmissibility of using oil as a fuel: "oil is not fuel - you can also heat banknotes." The possibility of a significant increase in the global energy balance of coal use is not ruled out. According to available calculations, the coal reserves are such that they can meet the world's energy needs for 200-300 years. Possible coal production, taking into account the explored and forecast reserves, is estimated at more than 7 trillion tons. At the same time, more than 1/3 of the world's coal reserves are located in Russia. Therefore, it is reasonable to expect an increase in the share of coals or products of their processing (for example, gas) in energy production, and, consequently, in environmental pollution. Coals contain from 0.2 to tens of percent sulfur mainly in the form of pyrite, ferrous sulfate and gypsum. The available methods of trapping sulfur during fuel combustion are not always used due to complexity and high cost. Therefore, a significant amount of it enters and, apparently, will enter the environment in the near future. Serious environmental problems are associated with solid waste from thermal power plants - ash and slag. Although the bulk of the ash is captured by various filters, nevertheless, about 250 million tons of fine aerosols enter the atmosphere annually in the form of emissions from thermal power plants.

The latter are able to noticeably change the balance of solar radiation near the earth's surface. They are also condensation nuclei for water vapor and precipitation formation, and when they get into the respiratory organs of humans and other organisms, they cause various respiratory diseases. TPP is a significant source of heated water, which is used here as a cooling agent. These waters often end up in rivers and other bodies of water, causing their thermal pollution and the accompanying chain natural reactions (algal growth, loss of oxygen, death of aquatic organisms, transformation of typical aquatic ecosystems into swamps, etc.).

Until recently, nuclear power was considered as the most promising. This is due both to the relatively large stocks of nuclear fuel and to the gentle impact on the environment. The advantages also include the possibility of building a nuclear power plant without being tied to resource deposits, since their transportation does not require significant costs due to small volumes. Suffice it to say that 0.5 kg of nuclear fuel allows you to get as much energy as burning 1000 tons of coal. Until the mid-1980s, mankind saw in nuclear energy one of the ways out of the energy impasse. In just 20 years (from the mid-1960s to the mid-1980s), the global share of energy produced at nuclear power plants increased from almost zero to 15-17%, and in a number of countries it became prevalent. No other type of energy has had such growth rates. Until recently, the main environmental problems of NPPs were associated with the disposal of spent fuel, as well as with the liquidation of NPPs themselves after the end of their permissible operating life. There is evidence that the cost of such liquidation works is from 1/6 to 1/3 of the cost of the NPPs themselves. Some parameters of NPP and TPP impact on the environment are presented in Table 8.3. At normal operation NPP releases of radioactive elements into the environment are extremely insignificant. On average, they are 2-4 times less than from thermal power plants of the same capacity. By May 1986, 400 power units operating in the world and providing more than 17% of electricity increased the natural background of radioactivity by no more than 0.02%. Before the Chernobyl disaster in our country, no industry had a lower level of industrial injuries than nuclear power plants. 30 years before the tragedy, accidents, and then for non-radiation reasons, killed 17 people. After 1986, the main environmental hazard of nuclear power plants began to be associated with the possibility of accidents. Although their probability at modern nuclear power plants is small, it is not excluded. The largest accidents of this kind include the Chernobyl nuclear power plant that happened at the fourth unit. The inevitable result of nuclear power plant operation is thermal water pollution. It is 2-2.5 times more per unit of energy received here than at thermal power plants, where much more heat is removed to the atmosphere. The production of 1 million kW of electricity at thermal power plants provides 1.5 km 3 of heated water, at nuclear power plants of the same power, the volume of heated water reaches 3-3.5 km 3. The result of large heat losses at nuclear power plants is their lower efficiency compared to TPP. At the latter, it is 35-40%, and at nuclear power plants - only 30-31%. In general, the following impacts of NPPs on the environment can be mentioned: - destruction of ecosystems and their elements (soils, soils, water-bearing structures, etc.) in ore mining sites (especially with an open method); - withdrawal of land for the construction of nuclear power plants themselves. Particularly significant territories are being alienated for the construction of facilities for the supply, removal and cooling of heated water. A 1000 MW power plant requires a cooling pond of about 800-900 ha. Ponds can be replaced by giant cooling towers with a diameter at the base of 100-120 m and a height equal to a 40-story building; - withdrawal of significant volumes of water from various sources and discharge of heated water. If these waters enter rivers and other sources, they experience a loss of oxygen, an increase in the probability of flowering, and an increase in the phenomena of heat stress in aquatic organisms; - radioactive contamination of the atmosphere, waters and soils during the extraction and transportation of raw materials, as well as during the operation of nuclear power plants, storage and processing of waste, and their disposal is not ruled out. Electromagnetic (EM) fields of industrial frequency currents, most dangerous places- at transformer substations, under high voltage power lines. The intensity of radiation is proportional to the fourth power of the frequency of oscillations of the electromagnetic field. The action of the EM field causes a violation of the functions of the nervous and cardiovascular systems, changes blood pressure.

2. Waysreceiving electrical energy

2.1 Power plants

Power station - an electrical station, a set of installations, equipment and apparatus used directly for the production of electrical energy, as well as the facilities and buildings necessary for this, located in a certain territory. Most power plants, whether hydroelectric, thermal (nuclear power plants, thermal power plants and others) or wind power plants, use the rotational energy of the generator shaft for their work.

1. Nuclear power plant

2. Thermal power plant

3. Wave power plant

4. Geothermal power plant

5. Tidal power plant

6. Hydrostorage power plant

Atomicpower station

Nuclear power plantnation(NPP) - a nuclear installation for the production of energy in specified modes and conditions of use, located within the territory defined by the project, in which a nuclear reactor (reactors) and a complex of necessary systems, devices, equipment and structures with the necessary workers (personnel) are used for this purpose ) for the production of electricity. In the second half of the 40s, even before the completion of work on the creation of the first Soviet atomic bomb (its test took place on August 29, 1949), Soviet scientists began to develop the first projects for the peaceful use of atomic energy, the general direction of which immediately became the electric power industry. In 1948, at the suggestion of I.V. Kurchatov and in accordance with the task of the party and the government, the first work began on the practical application of atomic energy to generate electricity. In May 1950, near the village of Obninskoye, Kaluga Region, work began on the construction of the world's first nuclear power plant. In 1950, the EBR-I reactor was created in the USA near the city of Arco, Idaho. This reactor on December 20, 1951, during the experiment, produced usable electricity with a power of 800 watts. After that, the power of the reactor was increased to provide electricity to the station where the reactor was located. This gives the right to call this station the first experimental nuclear power plant, but at the same time it was not connected to the power grid.

thermalpower station

A thermal power plant is a power plant that generates electrical energy by converting the chemical energy of fuel into mechanical energy of rotation of the shaft of an electric generator.

(TPP), a power plant at which, as a result of the combustion of fossil fuels, thermal energy, which is then converted into electricity. Thermal power plants are the main type of power plants, the share of electricity generated by them in industrialized countries is 70-80% (in Russia in 2000, approx. 67%). Thermal energy at thermal power plants is used to heat water and produce steam (at steam turbine power plants) or to produce hot gases (at gas turbine power plants). To obtain heat, organic fuel is burned in the boiler units of thermal power plants.

wave power plant

Wave power plant - a power plant located in the aquatic environment, the purpose of which is to obtain electricity from the kinetic energy of waves. The wave potential is estimated at more than 2 million MW. The places with the greatest potential for wave energy are the west coast of Europe, the north coast of Great Britain and the Pacific coast of North, South America, Australia and New Zealand, as well as the coast of South Africa.

The first wave power plant is located in the Agusadora region, Portugal, at a distance of 5 kilometers from the coast. It was officially opened on September 23, 2008 by the Portuguese Minister of Economy. The capacity of this power plant is 2.25 MW, which is enough to provide electricity to approximately 1,600 homes. Initially, it was assumed that the station would come into operation in 2006, but the deployment of the power plant took place 2 years later than planned. The power plant project belongs to the Scottish company Pelamis Wave Power, which in 2005 signed a contract with the Portuguese energy company Enersis to build a wave power plant in Portugal. The contract value was 8 million euros.

geothermal power plant

Geothermal power plant (GeoPP or GeoTPP) is a type of power plant that generates electrical energy from the thermal energy of underground sources (for example, geysers).

Geothermal energy is energy derived from the natural heat of the earth. This heat can be achieved with the help of wells. The geothermal gradient in the well increases by 1°C every 36 meters. This heat is delivered to the surface in the form of steam or hot water. Such heat can be used both directly for heating houses and buildings, and for the production of electricity. Thermal regions exist in many parts of the world. According to various estimates, the temperature at the center of the Earth is at least 6,650 °C. The rate of cooling of the Earth is approximately equal to 300--350 ° C per billion years. The Earth emits 42 1012 W of heat, of which 2% is absorbed in the crust and 98% in the mantle and core. Modern technology does not allow reaching heat that is released too deeply, but 840,000,000,000 W (2%) of available geothermal energy can meet the needs of mankind for for a long time. Areas around the edges of the continental plates are the best place to build geothermal plants because the crust in such areas is much thinner.

tidalpower station

A tidal power plant (TPP) is a special type of hydroelectric power plant that uses the energy of the tides, but in fact the kinetic energy of the Earth's rotation. Tidal power plants are built on the shores of the seas, where the gravitational forces of the Moon and the Sun change the water level twice a day. Water level fluctuations near the coast can reach 18 meters.

To obtain energy, the bay or the mouth of the river is blocked by a dam in which hydroelectric units are installed, which can operate both in generator mode and in pump mode (for pumping water into the reservoir for subsequent operation in the absence of tides). In the latter case, they are called a pumped storage power plant. There is an opinion that the operation of tidal power plants slows down the rotation of the Earth, which can lead to negative environmental consequences. However, due to the colossal mass of the Earth, the kinetic energy of its rotation (~1029 J) is so high that the operation of tidal stations with a total capacity of 1000 GW will increase the duration of the day by only ~10–14 seconds per year, which is 9 orders of magnitude less than natural tidal braking (~2 10?5 s per year).

Hydrostoragepower station

The pumped storage power plant uses in its work either a complex of generators and pumps, or reversible hydroelectric units that are capable of operating both in the mode of generators and in the mode of pumps. During the night power consumption dip, the PSP receives cheap electricity from the power grid and spends it on pumping water to the upstream (pumping mode). During the morning and evening peaks of power consumption, the PSP discharges water from the upstream to the downstream, while generating expensive peak electricity, which it gives to the power grid (generator mode). In large power systems, a large share can be the capacity of thermal and nuclear power plants, which cannot quickly electricity generation with a nightly decrease in energy consumption, or they do it with large losses. This fact leads to the establishment of a significantly higher commercial cost of peak electricity in the power system, compared to the cost of electricity generated during the night. Under such conditions, the use of a pumped storage power plant is economically efficient and increases both the efficiency of using other capacities (including transport ones) and the reliability of power supply.

Conclusion

Electrical energy is generated at power stations and transmitted to consumers mainly in the form of three-phase alternating current of industrial frequency 50 Hz. However, both in industry and in transport, there are installations for which alternating current with a frequency of 50 Hz is unsuitable.

Issues related to the conversion of electrical energy from one of its types to another are dealt with in the field of science and technology, called converter technology (or power electronics).

List of used literations

1. Reference technologist-machine builder. In 2 vols. Vol. 2 / ed. A.M. Dalsky, A.G. Kosilova, R.K. Meshcheryakova, A.G. Suslova. -5th ed., revised. and additional - M.: Mashinostroenie-1, 2001. -912 p.: ill.

2. Anuryev V.I. Handbook of the designer-machine builder: In 3 volumes. T. 1. - 8th ed., Revised. and additional Ed. I.N. Rigid. - M.: Mashinostroenie, 2001. -920 p.: ill.

3. Anuryev V.I. Handbook of the designer-machine builder: In 3 volumes. T. 2. - 8th ed., Revised. and additional Ed. I.N. Rigid. - M.: Mashinostroenie, 2001. -920 p.: ill.

4. Dunaev P.F., Lelikov O.P. Machine parts. Course design: Proc. Manual for mechanical engineering. specialist. technical schools. - M.: Higher. Shk., 1984. -336 p.: ill.

Hosted on Allbest.ru

...

Similar Documents

Calculation of DC circuit parameters using Kirchhoff equations, loop currents and nodal voltage method. Power balance calculation. Calculation of parameters of an alternating current circuit by the method of complex amplitudes. Resistivity connection conversion.

term paper, added 04/14/2015

AC to DC conversion. Ways to regulate the voltage of rectifiers. Block diagram of a thyristor converter of the KEMTOR series. Determination of the parameters of the matching transformer. Calculation of the external characteristics of the converter.

term paper, added 03/12/2013

Calculation of linear electric circuits of direct current, determination of currents in all branches of the methods of loop currents, imposition, folding. Nonlinear electrical circuits of direct current. Analysis of the electrical state of linear AC circuits.

term paper, added 05/10/2013

Features of control of electric motors of alternating current. Description of a frequency converter with an intermediate DC link based on an autonomous voltage inverter. Dynamic characteristics of automatic control systems of alternating current, stability analysis.

term paper, added 12/14/2010

Study of unbranched and branched DC electrical circuits. Calculation of non-linear DC circuits. Study of the operation of a direct current power line. AC circuit with series connection of resistances.

training manual, added 12/22/2009

Analysis of DC electrical circuits. Calculation of currents using Kirchhoff's laws. Calculation of currents by the method of loop currents. Calculation of currents by the nodal voltage method. The original table of current calculations. Potential diagram for a circuit with two EMF.

term paper, added 02.10.2008

Power source as a device designed to supply equipment with electrical energy. Converting AC voltage of industrial frequency into a pulsating DC voltage using rectifiers. DC voltage stabilizers.

abstract, added 02/08/2013

History of high-voltage power lines. The principle of operation of the transformer - a device for changing the magnitude of the voltage. Basic methods for converting large powers from direct current to alternating current. Associations of an electric network of alternating current.

practice report, added 11/19/2015

Electronic devices for converting AC energy into DC energy. Classification of rectifiers, their main parameters. The operation of a single-phase bridge rectification circuit. Diagrams of currents and voltages of a full-wave rectifier.

abstract, added 11/19/2011

The principle of operation and the device of the DC generator. Types of armature windings. Methods of excitation of DC generators. Reversibility of DC machines. Motor of parallel, independent, series and mixed excitation.

World energy consumption in all its forms, including electricity, is directly dependent on the population. The world's population has been growing especially significantly in recent times and by the year 2000, according to existing forecasts, it will be approximately 6 billion people. Dynamics of population growth in the second half of the XX century. is such that by 2000 the population had more than doubled compared to 1950 (Table 3.1). A large share of population growth is in developing countries. Along with the increase in the total energy consumption in the world, the share of energy per person is also growing (Table 3.1).

The huge demand for energy poses the problem of developing new ways of obtaining it for mankind. At present, it is no longer possible to be satisfied with the existing, traditional ways and conversion of various types of energy into electrical energy due to the limited reserves of fossil fuels, which are wastefully used when burned in furnaces. The efficiency of modern thermal power plants does not exceed 40%. This means that much of the heat received is lost and causes detrimental "thermal pollution" to nearby bodies of water. In addition, when burning fuel, the substance involved in the energy conversion process is poorly used. The efficiency factor for the use of the substance is negligible for TPPs.

Table 3.1

Consequently, the process of burning fuel is accompanied by huge emissions of by-products that pollute the environment. Therefore, the development of new methods of energy conversion, allowing to reduce waste emissions into the atmosphere, is one of the most important social problems. This, of course, does not mean that more modern thermal power plants, hydroelectric power plants and nuclear power plants do not correspond to the spirit of the times and their construction will be stopped.

In the foreseeable future, thermal power plants will remain one of the main ones, therefore, improving their design, improving the thermodynamic cycle is important for large-scale energy.

Great hopes are pinned on nuclear power plants, the introduction of which is taking place in many countries of the world at a rate unprecedented in the history of technology. It is expected that by the year 2000 the total capacity of nuclear power plants in the world will be 3500-3600 GW, while the total power capacity will reach 7000-7200 GW. In other words, it is assumed that at least 50% of the total energy capacity available to humanity will come from nuclear power plants. These figures indicate a high pace of development, especially if we consider that the first nuclear power plant was built in 1954.

In terms of the use of a substance at nuclear power plants, the efficiency is much higher than at thermal power plants (see Table 2.1), but on condition that this substance is specially prepared to perform the functions of nuclear fuel. At the same time, at nuclear power plants, the classical thermodynamic cycle of converting heat into mechanical energy, which is then converted into electrical energy by generators, leads to large losses of energy obtained in reactors. Thus, at modern nuclear power plants it is not possible to avoid the main fundamental shortcomings inherent in thermal power plants.

The tempting prospect of science is to get effective ways direct conversion of nuclear energy into electrical energy. Anticipating that great value, which nuclear energy is called upon to play in the history of mankind, Herbert Wells at the beginning of the 20th century. wrote; “... the dawn of power and freedom was already dawning under a sky illuminated by hope, before the face of science, which, like a beneficent goddess, held in strong hands over the pitch darkness of human life abundance, peace, the answer to countless riddles, the keys to the most glorious deeds, waiting, as long as people deign to take them ... ".

Widely used in many countries of the world, hydroelectric power stations built on rivers will continue to develop as very modern energy converters in a renewable form. In connection with the growing pollution of the biosphere and limited fuel reserves, there is an increasing interest in "clean" power plants that use the energy of sea tides, the heat of the earth's interior, and the energy of solar radiation.

Thus, along with the development of civilization and technological progress, the existing, which have become classic, will be improved, and new, more efficient ways of converting energy will be created. In the long term, humanity will have an arsenal of qualitatively different sources of energy, and what it uses today will inevitably become a thing of the past, just as steam engines have now become historical.

Despite the rapid progress in the energy sector and the high pace of building up the energy potential of the planet, energy production is not enough. We still have to face the reality that most of the world's population is starving, suffering from poverty and pollution.

In addition, energy consumption in the world (of different countries) is extremely uneven, and as shown above, energy consumption in a country is in a certain way related to the cultural level (see p. 19) of its population. The development of civilization and the production of material values are also directly related to the amount of energy consumed and its quality.

To improve the living conditions of people on the planet, to significantly increase labor productivity, to change landscapes on a large scale, as well as to solve a number of other vital problems, along with creating the necessary social conditions for development, it is important to obtain sufficiently large amounts of energy.

As the American scientists G. Seaborg and W. Corliss rightly write, "... cheap energy means food in abundance, an abundance of fresh water, clean air and all that is commonly called signs of civilization."

Shortage in modern world agricultural products poses the problem of increasing their production for the governments of a number of countries. To some extent, an increase in food can be obtained through the use of vacant land suitable for agriculture. However, these opportunities are not available in all countries in need of food and, moreover, they are limited. In conditions of a rapid increase in the population, the solution of the problem of food is possible only through the intensification of agriculture and, first of all, by irrigating the land. The supply of fresh water suitable for irrigation purposes is small. Since ancient times, people have dreamed of using the sea water washing the shores for agricultural needs. Desalination sea water on an industrial scale is becoming possible at the present time, when with the help of the most suitable nuclear power plants it has become available to obtain large quantities of heat necessary for the distillation of sea water.

According to existing estimates, 1/3 of the Earth is not inhabited due to lack of moisture, while 1/2 of the world's population is "pressed" on 1/10 of the land. With the help of cheap energy sources, it would be possible to turn the uninhabited territory of the Earth into a prosperous one, opening wide horizons for a significant part of the world's population.

Huge amounts of energy will also be required by humanity to solve such problems as climate change over vast areas by changing the direction of sea currents or building reservoirs with a large evaporation surface, transforming the landscape, building artificial sea bays, etc.

The methods used in modern energy production of electrical energy are accompanied by large losses and are based on the wasteful use of fossil fuels. In the future, as the demand for large amounts of cheap energy increases and natural raw materials are used more rationally for the production of products of the chemical, pharmaceutical industries, etc., the traditional methods of energy conversion will inevitably be replaced by qualitatively new methods, primarily methods of direct conversion heat and chemical energy into electrical energy.

Methods for the direct conversion of various types of energy into electrical energy are based on physical phenomena and effects discovered in the past. Their practical application is being improved with the progress in science and technology, the accumulation of rich experimental material and the use of latest technology. However, the methods of direct production of electrical energy are not yet competitive with the methods of energy conversion used in modern power plants. The direct production of electricity in large quantities by converting heat, chemical and nuclear energy is one of the new, promising methods that will undoubtedly become the main ones and will significantly increase the available energy resources of the planet.

The direct generation of electrical energy is already widely used in autonomous power sources of low power, for which the efficiency indicators are not of decisive importance, but reliability of operation, compactness, ease of maintenance, low weight, etc. are important. Such energy sources are used in information collection systems in hard-to-reach places on the Earth and in interplanetary space, on spacecraft, aircraft, ships, etc. The total installed capacity of billions of independent sources of electricity, despite their modest size, exceeds the capacity of all stationary power plants combined.

The work of autonomous sources that directly convert various types of energy into electrical energy is based either on chemical or physical effects. In chemical sources, for example, such as galvanic cells, batteries, electrochemical generators, etc., the energy of redox reactions of chemical reagents is used. Physical sources of electricity, such as thermionic generators, photovoltaic batteries, thermionic generators, operate in accordance with various physical effects.

One of the central physical and technical problems of power engineering is the creation of magnetohydrodynamic generators (MHD generators) that directly convert thermal energy into electrical energy. The possibilities of practical implementation of this kind of energy conversion on a large industrial scale appear in connection with the successes in atomic physics, plasma physics, metallurgy, and a number of other fields.

The direct conversion of thermal energy into electrical energy can significantly increase the efficiency of fuel resource use.

For modern electric power industry, the law of electromagnetic induction discovered by Faraday is of great importance, which states that an EMF is induced in a conductor moving in a magnetic field. The conductor may be solid, liquid or gaseous. The field of science that studies the interaction between a magnetic field and conductive liquids or gases is called magnetohydrodynamics.

Kelvin also showed that the movement of salt water at the mouth of a river in the Earth's magnetic field causes the appearance of an EMF. The scheme of such an MHD Kelvin generator is shown in Fig. 3.1. In accordance with the law of electromagnetic induction, the current strength in the conductors 1 attached to the plates 2, lowered into the water along the banks of the river, is proportional to the magnetic field induction! Earth and the speed of the flow of salty sea water in the river.1 When the direction of the flow of water in the river changed, the direction of the electric current in the conductors between the plates also changed.

The schematic diagram of the operation of a modern MHD-1 generator (Fig. 3.2) differs little from that shown in Fig. 3.1. In the scheme under consideration, a jet of ionized gas is passed between metal plates located in a strong magnetic field, which has the kinetic energy of the directed motion of particles. In this case, in accordance with the law of electromagnetic induction, an EMF appears, causing the flow of electric current between the electrodes! inside the generator channel and in the external circuit. The flow of ionized gas - plasma - is decelerated under the action of electrodynamic forces arising from the interaction of the current flowing in the plasma and the magnetic flux. An analogy can be drawn between the emerging forces and the braking forces acting from the side of the rotor blades of steam and gas turbines on particles of steam or gas. The transformation of energy occurs by doing work to overcome the braking forces.

If any gas is heated to a high temperature (~ 3000 ° C), thereby increasing its internal energy and turning it into an electrically conductive substance, then with the subsequent expansion of the gas in the working channels of the MHD generator, a direct conversion of thermal energy into electrical energy will occur.

Rice. 3.3. Schematic diagram of an MHD generator with a steam power plant: "- combustion chamber; 2 - heat exchanger; 3 - MHD generator; 4 - electromagnet winding; 5 - steam generator; 6 - turbine; 7 - generator; 3 - condenser; 9 - pump

A schematic diagram of an MHD generator with a steam power plant is shown in fig. 3.3. Organic fuel is burned in the combustion chamber, and the resulting products in the plasma state with the addition of additives are sent to the expanding channel of the MHD generator. A strong magnetic field is created by powerful electromagnets. The temperature of the gas in the generator channel must be at least 2000°C, and in the combustion chamber 2500-2800°C. The need to limit the minimum temperature of gases leaving MHD generators is caused by such a significant decrease in the electrical conductivity of gases at temperatures below 2000°C that their magnetohydrodynamic interaction with the magnetic field practically disappears.

The heat of gases exhausted in MHD generators is first used to heat the air supplied to the fuel combustion chamber and, consequently, to increase the efficiency of its combustion process. Then, in the steam power plant, the heat is spent on the formation of steam and bringing its parameters to the required values.

The gases leaving the channel of the MHD generator have a temperature of about 2000°C, and modern heat exchangers, unfortunately, can operate at temperatures not exceeding 800°C; therefore, part of the heat is lost when the gases are cooled.

On fig. 3.4 (see flyleaf II) schematically shows the main elements of an MHD power plant with a steam power plant and their relationships.

Difficulties in the creation of MHD generators lie in obtaining materials of the required strength. Despite the static working conditions, high demands are placed on materials, since they must work for a long time in aggressive environments at high temperatures (2500-2800°C). For the needs of rocket technology, materials have been created that can work in such conditions, but they can work for a short time - within minutes. The duration of operation of industrial power plants should be calculated at least in months.

Heat resistance depends not only on materials, but also on the environment. For example, a tungsten filament in an electric lamp at a temperature of 2500-2700°C can work in a vacuum or neutral gas environment for several thousand hours, and melts in air after a few seconds.

Lowering the plasma temperature by adding additives to it causes increased corrosion of structural materials. Currently, materials have been created that can work for a long time at a temperature of 2200-2500°C (graphite, magnesium oxide, etc.), but they are not able to withstand mechanical stresses.

Despite the successes achieved, the problem of creating materials for an MHD generator has not yet been solved. The search for gas with the best properties is also underway. Helium with a small addition of cesium at a temperature of 2000°C has the same conductivity as the combustion products of mineral fuel at a temperature of 2500°C. A project has been developed for an MHD generator operating in a closed cycle, in which helium continuously circulates in the system.

For the operation of an MHD generator, it is necessary to create a strong magnetic field, which can be obtained by passing huge currents through the windings. In order to avoid strong heating of the windings and energy losses in them, the resistance of the conductors should be as low as possible. Therefore, it is expedient to use superconducting materials as such conductors.

MHD generators with nuclear reactors. Promising are MHD generators with nuclear reactors used for heating gases and their thermal ionization. The proposed scheme of such an installation is shown in Fig. 3.5.

The difficulties in creating an MHD generator with a nuclear reactor are that modern fuel elements containing uranium and coated with magnesium oxide allow a temperature not much higher than 600 ° C, while for the ionization of gases, a temperature of approximately 2000°С.

The first experimental designs of MHD generators are still very expensive. In the future, a significant reduction in their cost can be expected, which will make it possible to successfully use MHD generators to cover load peaks in power systems, i.e., in modes of relatively short operation. In these regimes, the efficiency is not critical, and MHD generators can be used without a steam power addition.

Powerful prototypes of MHD energy converters have now been built in the USSR, on which research is underway to improve their design and create efficient MHD power plants that are competitive with conventional power plants.

Rice. 3.5. Project of an MHD generator with a nuclear reactor:

1 - nuclear reactor; 2 - nozzle; 3 - MHD generator; 4 - place of condensation of alkali metals; 5 - pump; 6 - place of input of alkali metals

Of all the devices that directly convert thermal energy into electrical energy, thermoelectric generators (TEG) of relatively low power are used most widely.

Main advantages of TEG: 1) there are no moving parts; 2) no need for high pressures; 3) any heat source can be used;

4) there is a large resource of work.

TEGs are widely used as energy sources in space objects, rockets, submarines, lighthouses, and many other installations.

Depending on the purpose, TEGs can convert into electrical energy the heat obtained in nuclear reactors, the energy of solar radiation, the energy of fossil fuels, etc. late 50s.

The operating principle of the thermoelement is based on the Seebeck effect. In 1921, Seebeck reported on experiments involving the deflection of a magnetic needle near thermoelectric circuits. In these studies, Seebeck did not consider the problem of obtaining energy. The essence of the open effect is that in a closed circuit consisting of dissimilar materials, current flows at different temperatures of the contacts of the materials.

The Seebeck effect can be qualitatively explained by the fact that the average energy of free electrons is different in different conductors and increases in different ways with increasing temperature. If there is a temperature difference along the conductor, then a directed flow of electrons from the hot junction to the cold junction occurs, as a result of which an excess of negative charges forms at the cold junction, and an excess of positive charges at the hot junction. This flow is more intense in conductors with a high concentration of electrons. In the simplest thermoelement, the closed circuit of which consists of two conductors with different electron concentrations and the junctions are maintained at different temperatures, an electric current arises. If the thermoelement circuit is open, then the accumulation of electrons at the cold end increases its negative potential until a dynamic equilibrium is established between the electrons moving towards the cold end and the electrons leaving the cold end under the action of the potential difference that has arisen. The lower the electrical conductivity of the material, the lower the rate of reverse flow of electrons, therefore, the higher the EMF. Therefore, semiconductor elements are more efficient than metals.

One of the practical applications of TEGs is a heat pump that releases heat in one part and absorbs heat in the other due to electrical energy. If you change the direction of the current, then the pump will work in the opposite mode, i.e., the parts in which heat is released and absorbed will change places. Such heat pumps can be successfully used for thermoregulation of residential and other premises. In winter, pumps heat the air in the room and cool it outside (Figure 3.6, a), and in summer, on the contrary, they cool the air in the room and heat it outside (Figure 3.6, b). On fig. 3.6, c shows a general view and installation diagram of a heat pump in a room.

At present, semiconductors have been created that operate at temperatures above 500°C. However, for commercial TEG, the hot junction temperature will need to be raised to about 1100°C. With such an increase in temperature, semiconductors of various types tend to become semiconductors proper, in which the numbers of carriers of positive and negative charges are equal. These charges, when creating a temperature gradient, move from the hot junction to the cold junction in equal amounts and, therefore, potential accumulation does not occur, i.e., no thermo-EMF is created. Semiconductors proper are useless for the purpose of generating thermoelectric current.

Currently, research is being carried out on the creation of semiconductors operating at high temperatures. For the operation of the TEG, it is possible to use the heat obtained in reactors during the fission of the nuclei of heavy elements. However, in this case, it is necessary to solve a number of problems, in particular, to determine the influence of the effect of strong radiation exposure on semiconductor materials, since nuclear fuel can be in direct contact with semiconductor materials.

The question of the expediency of using certain energy sources is decided in favor of TEG in cases where the leading value is not efficiency, but compactness, reliability, portability, and convenience.

In the USSR, a reliable industrial TEG on nuclear fuel - "Romashka" was created. Its electrical power is 500 watts.

The natural radioactive decay of nuclei is accompanied by the release of kinetic energy of particles and y-quanta. This energy is absorbed by the environment surrounding the radioactive isotope and converted into heat, which can be used to generate electrical energy in a thermoelectric way. Installations that convert the energy of natural radioactive decay into electrical energy using thermoelements are called radioisotope thermogenerators. Radioisotope thermogenerators are reliable in operation, have a long service life, are compact and are successfully used as autonomous power sources for various space and ground installations.

Modern radioisotope generators have an efficiency of 3-5% and a service life of 3 months to 10 years. The technical and economic characteristics of these generators can be significantly improved in the future. At present, projects of generators with power up to 10 kW are being created.

Various branches of science and technology are showing interest in radioisotope thermogenerators. They are supposed to be used as a source of energy for an artificial human heart, as well as to stimulate the work of various organs in living organisms. Radioisotope thermogenerators turned out to be especially suitable for space exploration, where energy sources are needed that can work for a long time and reliably under adverse conditions of exposure to ionizing radiation, in radiation belts, on the surface of other planets and their satellites.

The phenomenon of thermionic emission was discovered by T. Edison in 1883. Working on the creation of an electric lamp, Edison placed two filaments in a flask. When one of them burned out, he turned the lamp and turned on the other. During the testing of the lamps, it was found that a certain amount of electricity passes to the cold filament, i.e., the electrons "evaporate" from the hot filament - the cathode - and move to the cold filament - the anode - and further into the external electrical circuit. In this case, part of the thermal energy spent on heating the cathode is transferred by electrons and given to the anode, and part of the electron energy is released in the external electrical circuit when an electric current flows.

The anode is heated by the heat brought by the electrons. If the temperatures of the cathode and anode were the same, then the heat of "evaporation" of electrons from the cathode would be exactly equal to the heat of "condensation" of electrons on the anode and there would be no conversion of heat into electrical energy. The lower the anode temperature compared to the cathode temperature, the greater part of the thermal energy is converted into electrical energy. The simplest circuit thermionic energy converter is shown in fig. 3.7.

Rice. 3.7. Thermionic transducer device

energy: 1 - cathode; 2 - anode

In the process of thermionic emission, free electrons are released from the surface of metals. Metals contain a large number of free electrons - about 6 × 10 21 in 1 cm 3. Inside the metal, the forces of attraction of an electron are balanced by positively charged nuclei (Fig. 3.8). Directly at the surface, the resultant attractive forces act on the electrons, to overcome which and go beyond the metal, the electron must have sufficient kinetic energy. An increase in kinetic energy occurs when the metal is heated.

Rice. 3.8. The emergence of resultant forces acting on an electron in a metal and near its surface

In energy thermionic generators, the cathode can be heated using the heat obtained as a result of a nuclear reaction. The scheme of the nuclear thermionic converter is shown in fig. 3.9. The efficiency of the first such converters was approximately 15%; according to existing forecasts, it can be brought up to 40%.

The emission of electrons in thermionic generators is caused by heating the cathode. During radioactive decay, electrons (p-rays) are emitted due to a natural property of the elements. Directly using this property, it is possible to carry out a direct conversion of nuclear energy into electrical energy (Fig. 3.10).

Rice. 3.9. Nuclear thermionic converter: 1 - protection; 2 - cooler; 3 - anode; 4-vacuum; 5 - cathode; b - nuclear fuel

Rice. 3.10. Scheme of installation for direct conversion of nuclear energy into electrical energy: 1-β-radioactive emitter; 2 - metal ampoule; 3 - metal vessel

Electrochemical generators directly convert chemical energy into electrical energy. The occurrence of EMF in a galvanic cell is associated with the ability of metals to send their ions into a solution as a result of molecular interaction between metal ions and molecules (and ions) of the solution.

Consider the phenomena that occur when a zinc electrode is lowered into a solution of zinc sulfate (ZnSO 4). Water molecules tend to surround the positive zinc ions in the metal (Fig. 3.11). As a result of the action of electrostatic forces, positive zinc ions pass into a solution of zinc sulfate. This transition is favored by the large dipole moment of water.

Along with the process of zinc dissolution, the reverse process of returning positive zinc ions to the zinc electrode when they reach the electrode as a result of thermal motion occurs.

As the positive ions pass into the solution, the negative potential of the electrode increases, preventing this transition. At a certain metal potential, dynamic equilibrium sets in, i.e., two counterflows of ions (from the electrode to the solution and vice versa) will be the same. This equilibrium potential is called the electrochemical potential of the metal relative to the given electrolyte.

Galvanic cells have found an important technical application in batteries, where the substance consumed during the selection of current is preliminarily accumulated on the electrodes when current is passed through them for some time from an external source (during charging). The use of batteries in the power industry is difficult due to the small reserve of active chemical fuel, which does not allow to obtain continuous electricity in large quantities. In addition, batteries are characterized by low power density.

Much attention in many countries of the world is paid to the direct conversion of the chemical energy of organic fuel into electrical energy, carried out in fuel cells. In these energy converters, higher efficiency values can be obtained than in thermal engines. In 1893, the German physicist and chemist Nernst calculated that the theoretical efficiency of the electrochemical process of converting the chemical energy of coal into electrical energy is 99.75%.

Rice. 3.11. The arrangement of electric charges that contribute to the transition of positive zinc ions into a solution of zinc sulfate

On fig. 3.12 shows a schematic diagram of a hydrogen-oxygen fuel cell. The electrodes in the fuel cell are porous. At the anode, the transition of positive hydrogen ions into the electrolyte occurs. The remaining electrons create a negative potential and move to the cathode in the external circuit. Oxygen atoms located on the cathode attach electrons to themselves, forming negative ions, which, by attaching hydrogen atoms from water, pass into solution in the form of hydroxyl ions OH-. Hydroxide ions combine with hydrogen ions to form water. Thus, when hydrogen and oxygen are supplied, the reaction of fuel oxidation by ions occurs with the simultaneous formation of a current in the external circuit. Since the voltage at the terminals of the cell is small (of the order of 1 V), the cells are connected in series into batteries. The efficiency of fuel cells is very high. Theoretically, it is close to unity, but in practice it is 60-80%.

The use of hydrogen as a fuel is associated with a high cost of operating fuel cells; therefore, possibilities are being sought for using other cheaper types of fuel, primarily natural and producer gas. However, satisfactory rates of the gas oxidation reaction occur at high temperatures of 800-1200 K, which precludes the use of alkali aqueous solutions as electrolytes. In this case, solid electrolytes with ionic conductivity can be used.

Currently, work is underway to create efficient high-temperature fuel cells. So far, the power density of fuel cells is still low. It is several times lower than that of internal combustion engines. However, advances in electrochemistry and constructive improvements in fuel cells will make it possible in the near future to use fuel cells in vehicles and energy. Fuel cells are silent, economical and have no harmful waste polluting the atmosphere.

Rice. 3.12. Scheme of a hydrogen-oxygen fuel cell:

1 - body; 2- cathode; 3 - electrolyte; 4 - anode

1. AC rectification - converting alternating current (usually industrial frequency) into direct current. This type of conversion has received the greatest development, since some of the consumers of electrical energy can only operate on direct current (electrochemical and electrometallurgical installations, direct current transmission lines, electrolysis baths, rechargeable batteries, radio equipment, etc.), while other consumers have better performance on direct current than on alternating current (regulated electric motors).
2. Inverting current - converting direct current into alternating current. The inverter is used in cases where the energy source generates direct current (DC generators, batteries and other chemical current sources, solar panels, magnetohydrodynamic generators, etc.), and consumers need AC power. In some cases, current inversion is necessary for other types of electrical energy conversion (frequency conversion, phase number conversion).
3. Frequency conversion - conversion of alternating current of one frequency (usually 50 Hz) into alternating current of a different frequency. Such a conversion is necessary to power adjustable AC drives, induction heating and metal melting installations, ultrasonic devices, etc.
4. Conversion of the number of phases. In some cases, there is a need to convert a three-phase current into a single-phase one (for example, to power electric arc furnaces) or, conversely, a single-phase current into a three-phase one. So, on electrified transport, a single-phase alternating current contact network is used, and on electric locomotives, auxiliary machines of three-phase current are used. In industry, three-phase-single-phase frequency converters with direct connection are used, in which, along with the conversion of the industrial frequency to a lower one, the three-phase voltage is also converted into a single-phase one.
3. Converting direct current of one voltage to direct current of another voltage (converting constant voltage). Such a transformation is necessary, for example, on a number of mobile objects, where the source of electricity is a battery or other low-voltage direct current source, and a higher direct voltage is required to power consumers (for example, power supplies for radio engineering or electronic equipment).

The emergence of new types of power semiconductor valves, close to the ideal controllable key element, has significantly changed the approach to the construction of valve converters. GTO (gate turn off thirystor) and insulated gate bipolar transistors (IGBTs) that have become widespread in recent years successfully cover the power range up to hundreds and thousands of kilowatts, their dynamic properties are constantly being improved, and their cost is constantly improving. output growth is declining. Therefore, they successfully replaced conventional thyristors with forced switching nodes. The areas of application of pulse voltage converters with new classes of devices have also expanded. Powerful switching regulators are rapidly developing for both stepping up and stepping down the DC supply voltage; pulse converters are often used in energy recovery systems from renewable sources (wind, solar radiation).

The energy coming through power lines is not always used in its pure form. To perform specific tasks, it is converted by electrical devices that change one or more parameters - the type of voltage, frequency, and others.

Electricity converters: classification

These devices are classified according to several criteria:

Kind of transformation.
Construction type.
Manageability.

Parameters that change

The following parameters are subject to transformation:

Type of voltage - from AC to DC and vice versa.
Amplitude values of current and voltage.
Frequency.

Construction types

These devices are divided into electrical and semiconductor.

Electromachine (rotary) consist of two machines, one is a drive, and the other is an actuator. For example, to convert AC to DC, an AC induction motor (drive) and a DC generator (executor) are used. Their disadvantage is their large size and weight. In addition, the total efficiency of the technological bundle is lower than that of a single electric machine.

Semiconductor (static) converters are built on the basis of electrical circuits consisting of semiconductor or lamp elements. Their efficiency is higher, the size and weight are small, but the quality of the electricity at the output is low.

Managed and unmanaged

If the magnitude of the change in the electrical energy parameter is fixed, then an uncontrolled converter is used. Such devices are used in the first stages of power supplies. An example is a power transformer that lowers the mains voltage from 220 to 12 volts.

Converters with variable parameters are actuators in controlled electrical circuits. For example, by changing the frequency of the supply voltage, the speed of rotation of asynchronous motors is regulated.

Power converters: device examples

Converters can perform either one function or several.

Change voltage type

Those devices that convert alternating current into direct current are called rectifiers. Acting on the contrary - inverters.

If this is an electrical machine device, then the rectifier consists of an asynchronous AC motor that rotates the rotor of a DC generator. The input and output lines do not have electrical contact.

The most common type of static rectifier circuit is the diode bridge. It has four elements (diodes) with one-way conduction, connected in opposite directions. After it, an electrolytic capacitor is necessarily placed, which smooths out the pulsating voltage.

There is a hybrid design that combines an electric machine and a static rectifier. This is an automobile generator, which is an alternating current machine, the stator windings of which are connected to a rectifier bridge with a capacitor.

Inverter circuits are used to start a continuous oscillation generator (multivibrator) built on thyristors or transistors. They are the basis of frequency converters.

Change of amplitude values

These are all types of transformers - step-down, step-up, ballast.

Controlled transformers are called rheostats. If they are connected in parallel with the source of electricity, they change the voltage. In series - current.

To absorb the heat released during the operation of powerful high-voltage network transformers, liquid (oil) cooling systems are used.

Frequency change

Frequency converters are both electric (rotary) and static.

The actuator of rotary frequency converters is a high-frequency asynchronous three-phase generator. Its rotor rotates an electric motor of direct or alternating current. Like a rotary rectifier, its input and output lines do not have electrical contact.

Inverter circuits used in static type frequency converters are controlled and uncontrolled. Increasing the frequency allows you to reduce the size of the devices. A transformer operating at 400 Hz is eight times smaller than a transformer operating at 50 Hz. This property is used to build compact welding inverters.

Energy, from the Greek word energeia - activity or action, is a general measure of various types of movement and interaction.

Energy is a quantitative measure of the action and interaction of all types of matter.

Types of energy : mechanical, electrical, thermal, magnetic, atomic.

Kinetic energy is the result of a change in the state of motion of material bodies.

Potential energy is the result of a change in the position of the parts of a given system.

mechanical energy- this is the energy associated with the movement of an object or its position, the ability to perform mechanical work.

Electricity energy is one of the perfect types of energy.

Its widespread use is due to the following factors:

· Obtaining in large quantities near the deposit of resources and water sources;

Possibility of transportation over long distances with relatively small losses;

· Ability to transform into other types of energy: mechanical, chemical, thermal, light;

· No environmental pollution;

· The introduction of fundamentally new progressive technological processes with a high degree of automation based on electricity.

Recently, due to environmental problems, the shortage of fossil fuels and their uneven geographical distribution, it becomes expedient to generate electricity using wind turbines, solar panels, small gas generators.

Thermal energy is widely used in modern industries and in everyday life in the form of steam, hot water, fuel combustion products.

The conversion of primary energy into secondary energy is carried out at the stations:

· At a thermal power plant TPP - thermal;

· Hydroelectric power stations HPPs – mechanical (energy of water movement);

· Hydrostorage station of HPSP - mechanical (energy of movement of water preliminarily filled in an artificial reservoir);

· Nuclear power plant NPP - nuclear (energy of nuclear fuel);

· Tidal power plant PES - tides.

In the Republic of Belarus, more than 95% of energy is generated at thermal power plants, which are divided into two types according to their purpose:

1. Condensing thermal power plants of KES are designed to generate only electrical energy;

2. Combined heat and power plants (CHP) where combined production of electric and heat energy is carried out.

Methods for obtaining and converting energy.

Mechanical energy is converted into heat - by friction, into chemical - by destroying the structure of matter, compression, into electrical - by changing the electromagnetic field of the generator.

Thermal energy is converted into chemical, into kinetic energy of motion, and this energy is converted into mechanical (turbine), into electrical (thermo emf)

Chemical energy can be converted into mechanical (explosion), thermal (heat of reaction), electrical (batteries).

Electrical energy can be converted into mechanical (electric motor), chemical (electrolysis), electromagnetic (electromagnet).

Electromagnetic energy - the energy of the Sun - into thermal (heating water), into electrical (photoelectric effect → solar energy), into mechanical (phone ringing).

Nuclear energy → into chemical, thermal, mechanical (explosion), controlled fission (reactor) → chemical + thermal.

TPP includes a set of equipment in which the internal chemical energy of the fuel is converted into thermal energy of water and steam, which is converted into mechanical rotational energy, which generates electrical energy.

The fuel supplied from the warehouse (C) to the steam generator (SG) during combustion releases thermal energy, which, heating the water supplied from the water intake (VZ), converts it into water vapor energy with a temperature of 550. In the turbine, the water vapor energy is converted into mechanical energy of rotation, transmitted to the generator (G), which turns it into electricity. In the steam condenser (K), the exhaust steam with a temperature of 123-125 gives off the latent heat of vaporization to the cooling water and is again fed into the boiler-supercharger in the form of a condenser using a circular pump (H).

The CHP scheme differs from the TPP in that a heat exchanger is installed instead of the condenser, where steam at a significant pressure heats the water supplied to the main heat mains.

nuclear power station

The scheme of nuclear power plants depends on the type of reactor; type of coolant; composition of the equipment and can be one-, two-, and three-circuit.

Single-loop nuclear power plant.

The steam is processed directly in the reactor and enters the steam turbine. The exhaust steam is condensed in a condenser and the condensate is pumped into the reactor. The scheme is simple, economical. However, the steam at the exit from the reactor becomes radioactive, which imposes increased requirements on biological protection and makes it difficult to monitor and repair equipment.

1-atomic reactor;

2-turbine;

3-electric generator;

4-water vapor condenser;

5-feed pump.

The difference between a TPP and a nuclear power plant is that the source of heat at a TPP is a steam boiler in which organic fuel is burned; at a nuclear power plant - a nuclear reactor, the heat in which is released by the fission of nuclear fuel, which has a high calorific value.

Transportation of thermal and electric energy.

Transportation of thermal energy.

The main consumers of thermal energy are industrial enterprises and housing and communal services.

A heat supply system is a complex of devices for the generation, transportation and use of heat.

The supply of thermal energy to consumers (heating system, ventilation, hot water supply and technological processes) consists of 3 interrelated processes: transfer of heat to the coolant, transportation of the coolant and use of the thermal potential of the coolant. Heat supply systems can be decentralized (local) and centralized.

Decentralized heat supply systems are systems in which 3 main links are combined and located in the same or adjacent premises. At the same time, the receipt of heat and the transfer of its air to the room are combined in one device and are located in heated rooms.

Centralized systems heat supply systems are systems in which heat is supplied from one heat source for many buildings, quarters, districts.

Thermal energy is transported by thermal networks.

The main elements of heat networks are the pipeline, the insulating structure, the supporting structure.

Laying of pipelines is carried out by aboveground and underground methods.

Transportation of electrical energy.

The transmission of electricity from enterprises that generate electricity to direct consumers is carried out using electrical networks, which are a combination of substations (step-up and step-down), switchgears and electrical lines (overhead or cable) connecting them, located on the territory of the district, locality consumer of electrical energy.

The main equipment that produces and distributes electricity includes:

· Synchronous generators that generate electricity (at thermal power plants - turbogenerators);

· Busbars that receive electricity from generators and distribute it to consumers;

· Switching devices-switches that turn on and off circuits in normal and emergency conditions, and disconnectors that relieve voltage from the provided parts of electrical installations and create a visible break in the circuit;

· Electric receivers of own needs (pumps, fans, emergency electric lighting, etc.).

Auxiliary equipment is designed to perform the functions of measurement, signaling, protection and automation, etc.

Home baking recipes with photos - step by step master classes