{"id":30,"date":"2018-12-14T10:02:18","date_gmt":"2018-12-14T10:02:18","guid":{"rendered":"http:\/\/pb.ee.pw.edu.pl\/pb\/iepe\/?post_type=chapter&p=30"},"modified":"2024-03-12T14:36:45","modified_gmt":"2024-03-12T14:36:45","slug":"lecture-2-electric-generators","status":"publish","type":"chapter","link":"http:\/\/pb.ee.pw.edu.pl\/pb\/iepe\/chapter\/lecture-2-electric-generators\/","title":{"raw":"Electric Generators","rendered":"Electric Generators"},"content":{"raw":"

Sources and forms of energy<\/h1>\r\nThe following sources and forms of energy have been used for conversion on electric energy:\r\n\u2022 primary fuels (organic: solid, liquid, gaseous and nuclear)\r\n\u2022 energy of waters (inland and high tides and low tides of the seas),\r\n\u2022 geothermic energy (heat from the interior of the earth),\r\n\u2022 wind energy,\r\n\u2022 solar energy,\r\n\u2022 energy from chemical reactions.\r\n

Thermal power stations<\/h1>\r\nAn enterprise generating electric energy on industrial scale and using for this purpose energy of organic (conventional) or nuclear fuels is called thermal power plant. The scheme of energy conversion in majority of thermal power plants takes place in three-steps.\r\n

\"\"<\/p>\r\n\r\n

Division of thermal power plants<\/h1>\r\nAccording to the type of the thermal engine, thermal power plants are divided into:\r\n\u2022 conventional steam power plants in which steam produced in a boiler is the working medium and it works in a steam turbine,\r\n\u2022 steam nuclear power plants, in which process of fission of nuclear fuels in a reactor transfers thermal energy to the working medium,\r\n\u2022 gas-turbine power stations in which gas, being the product of fuel burning, is the working medium and it works in a gas turbine,\r\n\u2022 internal-combustion power stations with combustion piston engines (usually Diesel).\r\n

Conceptual diagrams<\/h1>\r\nCondensing power plants steam as a main medium\r\n

\"\"<\/p>\r\nCondensing power plants gas as a main medium\r\n

\"\"<\/p>\r\n\r\n

Division of thermal power plants<\/h1>\r\nDivision of thermal power plants according to the type of energy output :\r\n\u2022 condensing power plants \u2013 using only electric energy in condensing turbine-generators (they do not use the heat of exhaust steam),\r\n\u2022 combined heat and power stations (CHP, cogeneration) \u2013 generating electric energy and thermal energy, which is given outside as steam or hot water, in the amount of at least 10% of produced energy. Electric and thermal energy are produced in a CHP simultaneously,\r\n\u2022 combined cooling, heat and power (CCHP, trigeneration) \u2013 generation of electricity and useful heating and cooling from the combustion of a fuel.\r\n\r\nThe terms cogeneration and trigeneration used above may also be applied to the power systems generating simultaneously electricity, heat and chemicals \u2013 e.g. syngas or hydrogen.\r\n\r\nIn technological process of thermal coal-fired power plant one can distinguish four important systems:\r\n\u2022 fuel \u2013 air - combustion gases system,\r\n\u2022 steam \u2013 water system,\r\n\r\nwhich corresponds to main working medium circulation,\r\n\r\n\u2022 cooling system of condensers,\r\n\u2022 system of electric power output from power station.\r\n\r\nI \u2013 fuel-air combustion gases system,\r\nII \u2013 thermal system,\r\nIII \u2013 cooling system,\r\nIV \u2013 system of power output\r\n

\"\"<\/p>\r\n\r\n

Steam nuclear power plants<\/h1>\r\n\u2022 Three basic elements can be used as a fuel: uranium, plutonium and thorium.\r\n\u2022 Isotopes Uranium-233, Uranium-235 and Plutonium-239 are the most commonly used.\r\n\u2022 In fission reactors the fuel is usually based on the metal oxide because the oxide melting point is much higher than that of the metal. It is already in the oxidized state, so it also cannot burn.\r\n\u2022 In the process of fission unstable nuclei are hit by a slow-moving neutron, they split, creating two daughter nuclei, two or three more neutrons and thermal energy. These neutrons then are hitting more nuclei. This creates a chain reaction.\r\n\u2022 Released heat is used to generate steam that drives a steam turbine.\r\n\r\nScheme of a thermal-neutron reactor:\r\n

\"\"<\/p>\r\n1 \u2013 fuel rods\r\n2 \u2013 moderator\r\n3 \u2013 coolant\r\n4 \u2013 control rods\r\n5 \u2013 neutron reflector\r\n6 \u2013 thermal shield\r\n7 \u2013 reactor\u2019s reservoir\r\n8 \u2013 concrete shield\r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n\r\n \r\n

Hydro power stations<\/h1>\r\nPotential energy of water-courses is used in hydro power stations. These water races must be dammed up to make the difference between lower and upper reservoir. Water flows from upper to lower reservoir through water turbines.\r\nThe most important parameters of water power station are:\r\n\u2022 installed power P,\r\n\u2022 discharge flow of the power station Q\r\nequal to the volume of water flowing through all the turbines of the power station during a unit of time, in m3\/s,\r\n\u2022 gross head\r\nequal to the static difference of levels between upper and lower water,\r\n\u2022 time of operation during 24 hours, week etc.\r\n\u2022 efficiency.\r\n\r\nIn principle hydro power stations may be divided into:\r\n\r\nRun-off-river power stations have no reservoir for water storage, they use continuous flow of water. Hydro power station in W\u0142oc\u0142awek is classical example of this type.\r\n\r\nPumped power stations \u2013 operate as power stations during load peaks and as pumping plants during off-peaks periods, pumping water from lower to upper reservoir.\r\n\r\nReservoir power stations have big water tanks which can store huge amount of water. They enable better readjustment of power plant to the needs of electric power system.\r\n

\"\"Cross-section of the hydro power plant in W\u0142oc\u0142awek:\r\n1, 2 \u2013 consolidation of the bottom by concrete blocks; 3 \u2013 drain gallery; 4 \u2013 grid cleaner; 5 \u2013 mobile hoods above generators; 6 \u2013 road bridge; 7 \u2013transformer station; 8 \u2013 room for the staff<\/p>\r\n\r\n

\"\"Reservoir power station with pumping unit in Solina<\/h2>\r\nDepending on the head in hydro power stations the following types of turbines are used:\r\n\u2022 At low and very low heads (3-80 cm) Kaplan turbines and pipe turbines, in which the turbine and generator in common enclosure are immersed in water.\r\n\u2022 At medium heads (50-600 cm) Francis and Deriac turbines are applied.\r\n\u2022 At high heads (300-2000 cm) Pelton turbines are used.\r\n\r\nHydrogenerators used in water power plants are synchronous generators with salient poles. Depending on the turbine type there are used generators with vertical or horizontal shaft with rotational speed 75-1000 r\/min. Generator\u2019s power is usually adjusted to turbine generating power. In case of reversible units, in pumped power stations, generator\u2019s power is adjusted to the pumps\u2019 power, because power needed for pumping is usually higher than power given by the turbine.\r\n\r\nThe largest hydro power plants in the world\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n\r\n
Rank<\/td>\r\nName<\/td>\r\nCountry<\/td>\r\nRiver<\/td>\r\nYears of completion<\/td>\r\nInstalled capacity [MW]<\/td>\r\n<\/tr>\r\n
1<\/td>\r\nThree Gorges Dam<\/td>\r\n\u00a0China<\/td>\r\nYangtze<\/td>\r\n2008<\/td>\r\n22,5<\/td>\r\n<\/tr>\r\n
2<\/td>\r\nItaipu Dam<\/td>\r\n\u00a0Brazil\u00a0\/ \u00a0Paraguay<\/td>\r\nParan\u00e1<\/td>\r\n1984<\/td>\r\n14,0<\/td>\r\n<\/tr>\r\n
3<\/td>\r\nXiluodu<\/td>\r\n\u00a0China<\/td>\r\nJinsha<\/td>\r\n2014<\/td>\r\n13,9<\/td>\r\n<\/tr>\r\n
4<\/td>\r\nGuri<\/td>\r\n\u00a0Venezuela<\/td>\r\nCaron\u00ed<\/td>\r\n1978<\/td>\r\n10,2<\/td>\r\n<\/tr>\r\n
5<\/td>\r\nTucuru\u00ed<\/td>\r\n\u00a0Brazil<\/td>\r\nTocantins<\/td>\r\n1984<\/td>\r\n8,4<\/td>\r\n<\/tr>\r\n
6<\/td>\r\nGrand Coulee<\/td>\r\n\u00a0United States<\/td>\r\nColumbia<\/td>\r\n1942<\/td>\r\n6,8<\/td>\r\n<\/tr>\r\n
7<\/td>\r\nXiangjiaba<\/td>\r\n\u00a0China<\/td>\r\nJinsha<\/td>\r\n2014<\/td>\r\n6,4<\/td>\r\n<\/tr>\r\n
8<\/td>\r\nLongtan Dam<\/td>\r\n\u00a0China<\/td>\r\nHongshui<\/td>\r\n2007<\/td>\r\n6,4<\/td>\r\n<\/tr>\r\n
9<\/td>\r\nSayano\u2013Shushenskaya<\/td>\r\n\u00a0Russia<\/td>\r\nYenisei<\/td>\r\n1985<\/td>\r\n6,4<\/td>\r\n<\/tr>\r\n
10<\/td>\r\nKrasnoyarsk<\/td>\r\n\u00a0Russia<\/td>\r\nYenisei<\/td>\r\n1967<\/td>\r\n6,0<\/td>\r\n<\/tr>\r\n<\/tbody>\r\n<\/table>\r\n

Distributed generation<\/h1>\r\nDissipated (distributed) generation includes generating units with power, according to CIGRE (International Conference on Huge Transmission Networks), less than 50-100 MW, and according to EPRI (Electric Power Research Institute \u2013 USA) with power from a few kW to 50 MW. It contains the following types of units:\r\n\u2022 RES \u2013 renewable energy sources\r\nIn particular it is energy of rivers, wind, biomass and energy of solar radiation in solar cells,\r\n\u2022 CHP \u2013 cogeneration units,\r\n\u2022 DG \u2013 units with modular construction.\r\n

Hydro power stations<\/h1>\r\nSmall hydro power plants, with installed power up to 5 MW and efficiency up to 90%, are very attractive for the environment.\r\nTheir particular advantage is fast start-up and possibility of nearly immediate loading. They use the potential of tiny rivers, agricultural retention reservoirs, irrigation systems, water supply systems, sewage systems and by-channels.\r\nThey can be built in 1-2 years. Their technical simplicity guarantees high reliability and long time of operation. They need few staff and may be remotely controlled.\r\n

Wind power plants<\/h1>\r\nFrom renewable electric energy sources wind power plants gained the greatest success. Annual rise of over twenty percent of installed power was observed in wind power plants in recent years. From the technical point of view wind power plants are divided into:\r\n\u2022 autonomic wind power plants with synchronous generators, working in separated network or cooperating with the network of power industry through thyristor\/transistor converters,\r\n\u2022 wind power plants with asynchronous generators cooperating with electric power network individually or in the farm system.\r\n\r\nStructure of wind turbine V80 Vestas (2MW)\r\n1. controller,\r\n2. servo-motor of the device setting blades,\r\n3. main shaft,\r\n4. oil cooler,\r\n5. gear box,\r\n6. control system,\r\n7. outage brake,\r\n8. lift for the staff,\r\n9. transformer,\r\n10. blade spider,\r\n11. blade bearing,\r\n12. blade,\r\n13. rotor braking system,\r\n14. hydraulic system,\r\n15. disk of rotor braking hydraulic system,\r\n16. ring of directional system,\r\n17. carrying frame,\r\n18. gear of directional system,\r\n19. generator,\r\n20. generator cooler\r\n

\"\"<\/p>\r\nBasic advantage of wind power stations is that they generate electric energy using inexhaustible energy source and they do not send harmful substances to natural environment.\r\n\r\nBasic disadvantages of wind power plants are:\r\n\u2022 emission of noise during operation,\r\n\u2022 they cause electromagnetic disturbances,\r\n\u2022 they need large areas,\r\n\u2022 they deform the landscape,\r\n\u2022 they kill birds and bats in the radius of several km,\r\n\u2022 they work only at suitable speeds of the wind.\r\n\r\nKey facts:\r\n\u2022 Total capacity of wind turbines installed worldwide reached over 514 GW by the end of 2017 . More than 47 GW were added in the year 2017.\r\n\u2022 Installed wind turbines can cover more than 5% of the global electricity demand.\r\n\u2022 Globally the highest power installed in wind power plants is in China 188 GW, and highest share is in Denmark with 43% of its power coming from wind (5,3 GW).\r\n\u2022 The highest power installed in wind power plants in Europe is now in Germany \u2013 it is over 56 GW. There is about 6500 MW installed now in Poland.\r\n

Photovoltaic system<\/h1>\r\nPhotovoltaic cells are commonly used in countries with high insolation. They are formed of semi-conductive material, which under influence of solar radiation absorption generates direct electric current, taking advantage of photovoltaic effect.\r\n

\"\"\"\"Monocrystalline panels \u2013 oldest type of PV panels\r\n\u2022 Typical single cell has an area of about 100 cm2 and at full light generates power of about 1.5 W at the voltage of 0.5 V.\r\n\u2022 Voltage remains quasi constant, independently from light intensity, and current is directly proportional to the intensity of solar radiation.\r\n\u2022 To receive higher voltages and currents, the cells are connected in series and in parallel in so called photovoltaic modules of power from <50 W to ~300 W.\r\n\u2022 Currently monocrystalline panels are the most efficient (typically ~20%) type of PV panels.\r\n\u2022 Single cells are made through the Czochralski method where a silicon crystal \u2018seed\u2019 is placed in a vat of molten silicon. Then seed is slowly drawn up with the molten silicon forming a solid crystal structure around the seed known as an ingot which is later sliced to a silicon wafers. This is then made into a cell.<\/p>\r\nPolicrystalline (Multicrystalline) panels\r\n\u2022 Polycrystalline cells are slightly less efficient than Monocrystalline (typically 14-16%, last developments up to 21% )\r\n\u2022 They have become the dominant technology on the residential solar panels market because of the cheaper method of production.\r\n\u2022 Polycrystalline \u201ccell\u201d also start as a silicon crystal \u2018seed\u2019 placed in a vat of molten silicon that is allowed to cool, which forms the distinctive edges and grains in the solar cell.\r\nThin film panels\r\n\u2022 Thin film panels are a totally different technology \u2013 a photovoltaic substance is deposed onto a solid surface like glass.\r\n\u2022 Commercially used photovoltaic substances used are: Amorphous Silicon, Cadmium Telluride (CdTe), Copper indium gallium selenide (CGIS), Dye-sensitized solar cell (DSC).\r\n\u2022 They have the lowest efficiency (7-13%). However, with lowest material costs for thin film they are quickly becoming the more economically efficient.\r\n

Biomass power stations<\/h1>\r\nBiomass power stations are becoming more and more common. Electric energy generation from biomass may take place through its direct burning in power stations or CHP\u2019s or by burning biogas, oil or alcohol produced from biomass.\r\n\r\nBiomass fuels come from:\r\n\u2022 wood cuttings in forests,\r\n\u2022 waste wood from sawmills, furniture factories and others,\r\n\u2022 plants (i.e. straw) grown with the specific purpose of becoming biomass fuel.\r\n\r\nBiogas is derived from organic matter digested by microorganisms in a process that produces gas as a result (mixture of 65% methane (CH4) and of 35% CO2).\r\nThe anaerobic digestion process occurs naturally with waste at landfills.\r\n\r\nCarbon dioxide CO2 is a by-product of biomass combustion. But in this case it is neutral for natural environment, because through photosynthesis it circulates in closed cycle. There are no sulphur compounds in the combustion gases. However, the biomass may be polluted by pesticides and plastics waste, and in that case dioxins and furans, having toxic properties, may be send to the atmosphere.\r\n

Geothermal power stations<\/h1>\r\nGeothermal power stations belong to the renewable energy sources. Depending on water temperature and the content of gases and salt, the following solutions are possible:\r\n\u2022 high-temperature \u2013 steam from the deposit drives turbines directly,\r\n\u2022 low-temperature \u2013 steam heats low-boiling medium which drives a turbine,\r\n\u2022 high-pressure with methane \u2013 burned methane and water drive a 3-stage turbine in three cycles with lowering pressure and temperature.\r\n\r\nBasic types of geothermal power plants:\r\n\u2022 Dry steam plants \u2013 steam comes directly from a geothermal reservoir to turn generator turbines.\r\n\u2022 Flash steam plants - high-pressure hot water comes from deep inside the earth and converts to steam to drive generator turbines. Cooled, condensed steam is injected back into the ground to be used again. This is most common type of geothermal power plant.\r\n\u2022 Binary cycle power plants \u2013 heat is transferred from geothermal hot water to steam heater by another liquid.\r\n

Reciprocating engines<\/h1>\r\nReciprocating engines (also known as piston engines) are spark-ignition or diesel units with powers from 30 kW to 10 MW. They are running on the combustion of petrol, diesel, Liquefied petroleum gas (LPG) or compressed natural gas (CNG).\r\nThese generators are useful in small electric power systems because of:\r\n\u2022 low powers,\r\n\u2022 modular structure,\r\n\u2022 low capital costs and\r\n\u2022 short time of construction.\r\nThey are characterized by fast start-up, high reliability, they can follow characteristic of the receiver and they can recover heat.\r\nThese generators can serve as reserve-, peak-generators. They can be cogeneration- and working-on-separated-network units.\r\n

Gas miniturbines and microturbines<\/h1>\r\nGas miniturbines and microturbines are high reliability and availability generators, powered by natural gas, oil or working in bi-fuel system with powers from 30 kW to 5 MW.\r\n\r\nThey are characterized by:\r\n\u2022 high efficiency (especially at cogeneration),\r\n\u2022 low levels of emitted atmospheric polluters,\r\n\u2022 light construction,\r\n\u2022 low investment costs,\r\n\u2022 fast start-up,\r\n\u2022 high flexibility,\r\n\u2022 possibility of remote control.\r\n\r\nThey may work as CHP units.\r\n

Fuel cells<\/h1>\r\nFuel cell is an electrochemical converter of fuel chemical energy (hydrogen, natural gas) directly into electric energy with efficiency up to 50%.\r\nThe fuel is supplied in a continuous way to the anode, while an oxidizer (pure oxygen or air) is also given in a continuous way to the cathode.\r\nElectrolyte allows positively charged hydrogen ions (protons) to move between the two sides of the fuel cell.\r\nFuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.\r\nFuel cell efficiency is typically between 40\u201360% and up to 85% in a cogeneration scheme.\r\n

\"\"<\/p>\r\nAdvantages of fuel cells:\r\n\u2022 minimum amount of pollutions,\r\n\u2022 simple adjustment to the changing energy demand,\r\n\u2022 easy installation and fully automatic work,\r\n\u2022 possibility of usage in cogeneration systems and low exploitation costs.\r\n\r\nFuel cells are divided according to the electrolyte membrane used in them:\r\n\u2022 PAFC ( Phosphoric Acid Fuel Cell ) \u2013 temperature of work 200 C,\r\n\u2022 MCFC ( Molten Carbonate Fuel Cell ) \u2013 temperature of work 650 C,\r\n\u2022 SOFC ( Solid Oxide Fuel Cell) \u2013 temperature of work 1000 C,\r\n\u2022 PEMFC (Proton Exchange Membrane Fuel Cell) \u2013 polymer, temperature of work 800 C.\r\n\r\n ","rendered":"

Sources and forms of energy<\/h1>\n

The following sources and forms of energy have been used for conversion on electric energy:
\n\u2022 primary fuels (organic: solid, liquid, gaseous and nuclear)
\n\u2022 energy of waters (inland and high tides and low tides of the seas),
\n\u2022 geothermic energy (heat from the interior of the earth),
\n\u2022 wind energy,
\n\u2022 solar energy,
\n\u2022 energy from chemical reactions.<\/p>\n

Thermal power stations<\/h1>\n

An enterprise generating electric energy on industrial scale and using for this purpose energy of organic (conventional) or nuclear fuels is called thermal power plant. The scheme of energy conversion in majority of thermal power plants takes place in three-steps.<\/p>\n

\"\"<\/p>\n

Division of thermal power plants<\/h1>\n

According to the type of the thermal engine, thermal power plants are divided into:
\n\u2022 conventional steam power plants in which steam produced in a boiler is the working medium and it works in a steam turbine,
\n\u2022 steam nuclear power plants, in which process of fission of nuclear fuels in a reactor transfers thermal energy to the working medium,
\n\u2022 gas-turbine power stations in which gas, being the product of fuel burning, is the working medium and it works in a gas turbine,
\n\u2022 internal-combustion power stations with combustion piston engines (usually Diesel).<\/p>\n

Conceptual diagrams<\/h1>\n

Condensing power plants steam as a main medium<\/p>\n

\"\"<\/p>\n

Condensing power plants gas as a main medium<\/p>\n

\"\"<\/p>\n

Division of thermal power plants<\/h1>\n

Division of thermal power plants according to the type of energy output :
\n\u2022 condensing power plants \u2013 using only electric energy in condensing turbine-generators (they do not use the heat of exhaust steam),
\n\u2022 combined heat and power stations (CHP, cogeneration) \u2013 generating electric energy and thermal energy, which is given outside as steam or hot water, in the amount of at least 10% of produced energy. Electric and thermal energy are produced in a CHP simultaneously,
\n\u2022 combined cooling, heat and power (CCHP, trigeneration) \u2013 generation of electricity and useful heating and cooling from the combustion of a fuel.<\/p>\n

The terms cogeneration and trigeneration used above may also be applied to the power systems generating simultaneously electricity, heat and chemicals \u2013 e.g. syngas or hydrogen.<\/p>\n

In technological process of thermal coal-fired power plant one can distinguish four important systems:
\n\u2022 fuel \u2013 air – combustion gases system,
\n\u2022 steam \u2013 water system,<\/p>\n

which corresponds to main working medium circulation,<\/p>\n

\u2022 cooling system of condensers,
\n\u2022 system of electric power output from power station.<\/p>\n

I \u2013 fuel-air combustion gases system,
\nII \u2013 thermal system,
\nIII \u2013 cooling system,
\nIV \u2013 system of power output<\/p>\n

\"\"<\/p>\n

Steam nuclear power plants<\/h1>\n

\u2022 Three basic elements can be used as a fuel: uranium, plutonium and thorium.
\n\u2022 Isotopes Uranium-233, Uranium-235 and Plutonium-239 are the most commonly used.
\n\u2022 In fission reactors the fuel is usually based on the metal oxide because the oxide melting point is much higher than that of the metal. It is already in the oxidized state, so it also cannot burn.
\n\u2022 In the process of fission unstable nuclei are hit by a slow-moving neutron, they split, creating two daughter nuclei, two or three more neutrons and thermal energy. These neutrons then are hitting more nuclei. This creates a chain reaction.
\n\u2022 Released heat is used to generate steam that drives a steam turbine.<\/p>\n

Scheme of a thermal-neutron reactor:<\/p>\n

\"\"<\/p>\n

1 \u2013 fuel rods
\n2 \u2013 moderator
\n3 \u2013 coolant
\n4 \u2013 control rods
\n5 \u2013 neutron reflector
\n6 \u2013 thermal shield
\n7 \u2013 reactor\u2019s reservoir
\n8 \u2013 concrete shield<\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

 <\/p>\n

Hydro power stations<\/h1>\n

Potential energy of water-courses is used in hydro power stations. These water races must be dammed up to make the difference between lower and upper reservoir. Water flows from upper to lower reservoir through water turbines.
\nThe most important parameters of water power station are:
\n\u2022 installed power P,
\n\u2022 discharge flow of the power station Q
\nequal to the volume of water flowing through all the turbines of the power station during a unit of time, in m3\/s,
\n\u2022 gross head
\nequal to the static difference of levels between upper and lower water,
\n\u2022 time of operation during 24 hours, week etc.
\n\u2022 efficiency.<\/p>\n

In principle hydro power stations may be divided into:<\/p>\n

Run-off-river power stations have no reservoir for water storage, they use continuous flow of water. Hydro power station in W\u0142oc\u0142awek is classical example of this type.<\/p>\n

Pumped power stations \u2013 operate as power stations during load peaks and as pumping plants during off-peaks periods, pumping water from lower to upper reservoir.<\/p>\n

Reservoir power stations have big water tanks which can store huge amount of water. They enable better readjustment of power plant to the needs of electric power system.<\/p>\n

\"\"Cross-section of the hydro power plant in W\u0142oc\u0142awek:
\n1, 2 \u2013 consolidation of the bottom by concrete blocks; 3 \u2013 drain gallery; 4 \u2013 grid cleaner; 5 \u2013 mobile hoods above generators; 6 \u2013 road bridge; 7 \u2013transformer station; 8 \u2013 room for the staff<\/p>\n

\"\"Reservoir power station with pumping unit in Solina<\/h2>\n

Depending on the head in hydro power stations the following types of turbines are used:
\n\u2022 At low and very low heads (3-80 cm) Kaplan turbines and pipe turbines, in which the turbine and generator in common enclosure are immersed in water.
\n\u2022 At medium heads (50-600 cm) Francis and Deriac turbines are applied.
\n\u2022 At high heads (300-2000 cm) Pelton turbines are used.<\/p>\n

Hydrogenerators used in water power plants are synchronous generators with salient poles. Depending on the turbine type there are used generators with vertical or horizontal shaft with rotational speed 75-1000 r\/min. Generator\u2019s power is usually adjusted to turbine generating power. In case of reversible units, in pumped power stations, generator\u2019s power is adjusted to the pumps\u2019 power, because power needed for pumping is usually higher than power given by the turbine.<\/p>\n

The largest hydro power plants in the world<\/p>\n\n\n\n\n\n\n\n\n\n\n\n\n\n
Rank<\/td>\nName<\/td>\nCountry<\/td>\nRiver<\/td>\nYears of completion<\/td>\nInstalled capacity [MW]<\/td>\n<\/tr>\n
1<\/td>\nThree Gorges Dam<\/td>\n\u00a0China<\/td>\nYangtze<\/td>\n2008<\/td>\n22,5<\/td>\n<\/tr>\n
2<\/td>\nItaipu Dam<\/td>\n\u00a0Brazil\u00a0\/ \u00a0Paraguay<\/td>\nParan\u00e1<\/td>\n1984<\/td>\n14,0<\/td>\n<\/tr>\n
3<\/td>\nXiluodu<\/td>\n\u00a0China<\/td>\nJinsha<\/td>\n2014<\/td>\n13,9<\/td>\n<\/tr>\n
4<\/td>\nGuri<\/td>\n\u00a0Venezuela<\/td>\nCaron\u00ed<\/td>\n1978<\/td>\n10,2<\/td>\n<\/tr>\n
5<\/td>\nTucuru\u00ed<\/td>\n\u00a0Brazil<\/td>\nTocantins<\/td>\n1984<\/td>\n8,4<\/td>\n<\/tr>\n
6<\/td>\nGrand Coulee<\/td>\n\u00a0United States<\/td>\nColumbia<\/td>\n1942<\/td>\n6,8<\/td>\n<\/tr>\n
7<\/td>\nXiangjiaba<\/td>\n\u00a0China<\/td>\nJinsha<\/td>\n2014<\/td>\n6,4<\/td>\n<\/tr>\n
8<\/td>\nLongtan Dam<\/td>\n\u00a0China<\/td>\nHongshui<\/td>\n2007<\/td>\n6,4<\/td>\n<\/tr>\n
9<\/td>\nSayano\u2013Shushenskaya<\/td>\n\u00a0Russia<\/td>\nYenisei<\/td>\n1985<\/td>\n6,4<\/td>\n<\/tr>\n
10<\/td>\nKrasnoyarsk<\/td>\n\u00a0Russia<\/td>\nYenisei<\/td>\n1967<\/td>\n6,0<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Distributed generation<\/h1>\n

Dissipated (distributed) generation includes generating units with power, according to CIGRE (International Conference on Huge Transmission Networks), less than 50-100 MW, and according to EPRI (Electric Power Research Institute \u2013 USA) with power from a few kW to 50 MW. It contains the following types of units:
\n\u2022 RES \u2013 renewable energy sources
\nIn particular it is energy of rivers, wind, biomass and energy of solar radiation in solar cells,
\n\u2022 CHP \u2013 cogeneration units,
\n\u2022 DG \u2013 units with modular construction.<\/p>\n

Hydro power stations<\/h1>\n

Small hydro power plants, with installed power up to 5 MW and efficiency up to 90%, are very attractive for the environment.
\nTheir particular advantage is fast start-up and possibility of nearly immediate loading. They use the potential of tiny rivers, agricultural retention reservoirs, irrigation systems, water supply systems, sewage systems and by-channels.
\nThey can be built in 1-2 years. Their technical simplicity guarantees high reliability and long time of operation. They need few staff and may be remotely controlled.<\/p>\n

Wind power plants<\/h1>\n

From renewable electric energy sources wind power plants gained the greatest success. Annual rise of over twenty percent of installed power was observed in wind power plants in recent years. From the technical point of view wind power plants are divided into:
\n\u2022 autonomic wind power plants with synchronous generators, working in separated network or cooperating with the network of power industry through thyristor\/transistor converters,
\n\u2022 wind power plants with asynchronous generators cooperating with electric power network individually or in the farm system.<\/p>\n

Structure of wind turbine V80 Vestas (2MW)
\n1. controller,
\n2. servo-motor of the device setting blades,
\n3. main shaft,
\n4. oil cooler,
\n5. gear box,
\n6. control system,
\n7. outage brake,
\n8. lift for the staff,
\n9. transformer,
\n10. blade spider,
\n11. blade bearing,
\n12. blade,
\n13. rotor braking system,
\n14. hydraulic system,
\n15. disk of rotor braking hydraulic system,
\n16. ring of directional system,
\n17. carrying frame,
\n18. gear of directional system,
\n19. generator,
\n20. generator cooler<\/p>\n

\"\"<\/div>\n

Basic advantage of wind power stations is that they generate electric energy using inexhaustible energy source and they do not send harmful substances to natural environment.<\/p>\n

Basic disadvantages of wind power plants are:
\n\u2022 emission of noise during operation,
\n\u2022 they cause electromagnetic disturbances,
\n\u2022 they need large areas,
\n\u2022 they deform the landscape,
\n\u2022 they kill birds and bats in the radius of several km,
\n\u2022 they work only at suitable speeds of the wind.<\/p>\n

Key facts:
\n\u2022 Total capacity of wind turbines installed worldwide reached over 514 GW by the end of 2017 . More than 47 GW were added in the year 2017.
\n\u2022 Installed wind turbines can cover more than 5% of the global electricity demand.
\n\u2022 Globally the highest power installed in wind power plants is in China 188 GW, and highest share is in Denmark with 43% of its power coming from wind (5,3 GW).
\n\u2022 The highest power installed in wind power plants in Europe is now in Germany \u2013 it is over 56 GW. There is about 6500 MW installed now in Poland.<\/p>\n

Photovoltaic system<\/h1>\n

Photovoltaic cells are commonly used in countries with high insolation. They are formed of semi-conductive material, which under influence of solar radiation absorption generates direct electric current, taking advantage of photovoltaic effect.<\/p>\n

\"\"\"\"Monocrystalline panels \u2013 oldest type of PV panels
\n\u2022 Typical single cell has an area of about 100 cm2 and at full light generates power of about 1.5 W at the voltage of 0.5 V.
\n\u2022 Voltage remains quasi constant, independently from light intensity, and current is directly proportional to the intensity of solar radiation.
\n\u2022 To receive higher voltages and currents, the cells are connected in series and in parallel in so called photovoltaic modules of power from <50 W to ~300 W.
\n\u2022 Currently monocrystalline panels are the most efficient (typically ~20%) type of PV panels.
\n\u2022 Single cells are made through the Czochralski method where a silicon crystal \u2018seed\u2019 is placed in a vat of molten silicon. Then seed is slowly drawn up with the molten silicon forming a solid crystal structure around the seed known as an ingot which is later sliced to a silicon wafers. This is then made into a cell.<\/p>\n

Policrystalline (Multicrystalline) panels
\n\u2022 Polycrystalline cells are slightly less efficient than Monocrystalline (typically 14-16%, last developments up to 21% )
\n\u2022 They have become the dominant technology on the residential solar panels market because of the cheaper method of production.
\n\u2022 Polycrystalline \u201ccell\u201d also start as a silicon crystal \u2018seed\u2019 placed in a vat of molten silicon that is allowed to cool, which forms the distinctive edges and grains in the solar cell.
\nThin film panels
\n\u2022 Thin film panels are a totally different technology \u2013 a photovoltaic substance is deposed onto a solid surface like glass.
\n\u2022 Commercially used photovoltaic substances used are: Amorphous Silicon, Cadmium Telluride (CdTe), Copper indium gallium selenide (CGIS), Dye-sensitized solar cell (DSC).
\n\u2022 They have the lowest efficiency (7-13%). However, with lowest material costs for thin film they are quickly becoming the more economically efficient.<\/p>\n

Biomass power stations<\/h1>\n

Biomass power stations are becoming more and more common. Electric energy generation from biomass may take place through its direct burning in power stations or CHP\u2019s or by burning biogas, oil or alcohol produced from biomass.<\/p>\n

Biomass fuels come from:
\n\u2022 wood cuttings in forests,
\n\u2022 waste wood from sawmills, furniture factories and others,
\n\u2022 plants (i.e. straw) grown with the specific purpose of becoming biomass fuel.<\/p>\n

Biogas is derived from organic matter digested by microorganisms in a process that produces gas as a result (mixture of 65% methane (CH4) and of 35% CO2).
\nThe anaerobic digestion process occurs naturally with waste at landfills.<\/p>\n

Carbon dioxide CO2 is a by-product of biomass combustion. But in this case it is neutral for natural environment, because through photosynthesis it circulates in closed cycle. There are no sulphur compounds in the combustion gases. However, the biomass may be polluted by pesticides and plastics waste, and in that case dioxins and furans, having toxic properties, may be send to the atmosphere.<\/p>\n

Geothermal power stations<\/h1>\n

Geothermal power stations belong to the renewable energy sources. Depending on water temperature and the content of gases and salt, the following solutions are possible:
\n\u2022 high-temperature \u2013 steam from the deposit drives turbines directly,
\n\u2022 low-temperature \u2013 steam heats low-boiling medium which drives a turbine,
\n\u2022 high-pressure with methane \u2013 burned methane and water drive a 3-stage turbine in three cycles with lowering pressure and temperature.<\/p>\n

Basic types of geothermal power plants:
\n\u2022 Dry steam plants \u2013 steam comes directly from a geothermal reservoir to turn generator turbines.
\n\u2022 Flash steam plants – high-pressure hot water comes from deep inside the earth and converts to steam to drive generator turbines. Cooled, condensed steam is injected back into the ground to be used again. This is most common type of geothermal power plant.
\n\u2022 Binary cycle power plants \u2013 heat is transferred from geothermal hot water to steam heater by another liquid.<\/p>\n

Reciprocating engines<\/h1>\n

Reciprocating engines (also known as piston engines) are spark-ignition or diesel units with powers from 30 kW to 10 MW. They are running on the combustion of petrol, diesel, Liquefied petroleum gas (LPG) or compressed natural gas (CNG).
\nThese generators are useful in small electric power systems because of:
\n\u2022 low powers,
\n\u2022 modular structure,
\n\u2022 low capital costs and
\n\u2022 short time of construction.
\nThey are characterized by fast start-up, high reliability, they can follow characteristic of the receiver and they can recover heat.
\nThese generators can serve as reserve-, peak-generators. They can be cogeneration- and working-on-separated-network units.<\/p>\n

Gas miniturbines and microturbines<\/h1>\n

Gas miniturbines and microturbines are high reliability and availability generators, powered by natural gas, oil or working in bi-fuel system with powers from 30 kW to 5 MW.<\/p>\n

They are characterized by:
\n\u2022 high efficiency (especially at cogeneration),
\n\u2022 low levels of emitted atmospheric polluters,
\n\u2022 light construction,
\n\u2022 low investment costs,
\n\u2022 fast start-up,
\n\u2022 high flexibility,
\n\u2022 possibility of remote control.<\/p>\n

They may work as CHP units.<\/p>\n

Fuel cells<\/h1>\n

Fuel cell is an electrochemical converter of fuel chemical energy (hydrogen, natural gas) directly into electric energy with efficiency up to 50%.
\nThe fuel is supplied in a continuous way to the anode, while an oxidizer (pure oxygen or air) is also given in a continuous way to the cathode.
\nElectrolyte allows positively charged hydrogen ions (protons) to move between the two sides of the fuel cell.
\nFuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.
\nFuel cell efficiency is typically between 40\u201360% and up to 85% in a cogeneration scheme.<\/p>\n

\"\"<\/p>\n

Advantages of fuel cells:
\n\u2022 minimum amount of pollutions,
\n\u2022 simple adjustment to the changing energy demand,
\n\u2022 easy installation and fully automatic work,
\n\u2022 possibility of usage in cogeneration systems and low exploitation costs.<\/p>\n

Fuel cells are divided according to the electrolyte membrane used in them:
\n\u2022 PAFC ( Phosphoric Acid Fuel Cell ) \u2013 temperature of work 200 C,
\n\u2022 MCFC ( Molten Carbonate Fuel Cell ) \u2013 temperature of work 650 C,
\n\u2022 SOFC ( Solid Oxide Fuel Cell) \u2013 temperature of work 1000 C,
\n\u2022 PEMFC (Proton Exchange Membrane Fuel Cell) \u2013 polymer, temperature of work 800 C.<\/p>\n

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