Hydraulic power plantHydraulic power plants utilize the potential energy of water as the source of energy for

power generation. Water is collected in natural lakes or reservoirs at high altitudes. Water is carried to the turbine through a pipe called penstock. The hydraulic turbine converts the potential and kinetic energy of water into mechanical energy. The rotating shaft of turbine is coupled to an electric generator, producing electricity.

The essential components of a hydel power plant include reservoir, dam, penstock, surge tank, trash rack, turbine, draft tube, generator and other equipments.Reservoir: Reservoir stores the water to run the turbines. Reservoir may be natural such as a lake or artificial reservoir can be built by erecting a dam across the river. Reservoir stores water during rainy season and supplies during summer.Dam: It is a structure of masonry or some other material built at suitable location across a river. Dam creates an artificial reservoir for the hydel power plant. Masonry dams can be of gravity, buttress or arch type.Penstock: It is a pipe made up of steel or concrete which carries water from the reservoir to the turbine. Penstock should be sloping towards the power house and sharp bends in the penstock should be avoided to reduce loss of head.Surge tank: It is an additional reservoir fitted in between the main reservoir and power house very much nearer to the power house. Water flow into the turbine is regulated as per the turbine load. When turbine load decreases, valves to turbine are partly closed and water moves back. This backward moving water gets stored in the surge tank and relieves the pressure in penstock.Trash Rack: Trash rack is provided to keep out debris from going through the penstock.Turbine: It converts the kinetic energy and pressure energy of water into mechanical energy. Hydraulic turbines can be of impulse or reaction type. Impulse turbines like Pelton wheel utilize the kinetic energy of water jet striking the runner to rotate it. In reaction turbines like Francis turbine and Kaplan turbine, the pressure difference between the runner inlet and exit also contributes to the rotation of runner.Generator: The turbine shaft is coupled to a generator which converts the mechanical energy produced by the turbine into electrical energy.

Advantages of hydro-electric plants1. Maintenance and operation costs are very low.2. Rapid fluctuating loads can be served most economically.

3. No waste disposal problems4. No atmospheric pollution.5. Also serves the purpose of irrigation and flood control.6. Comparatively a long life (50 - 100 years as against 20 - 45 years of a thermal plant).Limitations1. The initial cost of the plant is very high.2. Project duration is long.3. Power generation depends on the availability of water. 4. Cannot be located near the load centre

Diesel power plantDiesel power plants produces electric power by coupling diesel engine with an electric generator. Diesel power plants in the range of 2 to 50 MW capacities are used as central stations for small electric supply net works and used as standby to hydroelectric or thermal plants where continuous supply is needed.

The major components of a diesel power plant areEngine: Generally two stroke engines are used for power generation. It is directly connected through a gear box to the generator.Air supply system: Air from atmosphere after filtering is admitted to the engine. In large pants, superchargers or turbochargers are provided in the air supply line in order to increase the pressure of the input air which will ultimately increase the power output of the engine.Fuel system: Fuel is stored in a main storage tank located outside the power plant. Motor driven pumps take the fuel from the main storage tank to the day tank through a filter. The fuel from the day storage tank flows under gravity to the engine. Fuel pumps and injectors are used to inject the required amount of fuel into the cylinders at proper time.Cooling system: This includes water circulating pumps, cooling towers, water filters etc. The water used for cooling the engine is initially treated to make it free from impurities. This water is circulated through the lubricating oil cooler and through water jackets for cooling the engine. The circulating water coming out of engine is cooled by raw water in a heat exchanger. The raw water is cooled in cooling towers.Lubricating system: It includes the oil pumps, oil tanks, filters, oil coolers and connecting pipes. Filter is provided in a bypass arrangement so that a clogged filter will not restrict the flow of lubricating oil to the engine.

Starting system: Three types of starting system commonly in use are (a) petrol driven engine (b) use of electric motors and (c) use of compressed air from an air compressor at a pressure of 20kg/cm2.Governing system: The function of governing system is to maintain the speed of the engine constant irrespective of load on the plant. This is done generally by varying fuel supply to the engine according to load on the plant.

Advantages of diesel power plants1. It is easy to design and install.2. They can respond to load changes without much difficulty.3. They occupy less space.4. They can be started and stopped quickly.5. Capital cost is less.6. They can be located near the load centre.

Limitations1. High operating , maintenance and lubrication cost.2. Capacity is restricted. Cannot be of very big size.3. Noise problem.4. Cannot supply overload.5. Unhygienic emissions.6. Comparitively lesser life

Steam power plant/Thermal power plant/Coal power plantSteam is the working fluid used for generating mechanical energy. Steam is generated in

the boiler of thermal power plant by using the heat obtained from the combustion of fuel. The steam generated is passed through the steam turbine where the thermal energy of steam is utilised to run the turbine. The steam turbine is coupled to a generator for electric power generation. The steam turbines used can be of impulse or reaction type.

Various circuits in a steam power plant areFuel circuit: The fuel used in a steam power plant may be solid, liquid or gaseous or a combination. Figure shows a power plant with coal as fuel. The coal from the storage is fed to the

boiler furnace through coal handling equipments. The ash circuit includes the removal of ash from the boiler furnace to the sump.Air and gas circuit: Air is supplied through a blower to the boiler furnace. The exhaust gases are passed to the atmosphere through a chimney. The heat energy of exhaust gases is used in a pre-heater to preheat the air entering boiler furnace. An economiser utilises the heat energy of exhaust gases to preheat the feed water entering the boiler. Air pre-heater and economiser increases the thermal efficiency of boiler.Feed water and steam circuit: The steam generated in the boiler is supplied to the turbine to develop mechanical power. The steam coming out of the turbine is condensed in the condenser and fed back to the boiler with the help of a feed pump. Loss in feed water is compensated by makeup feed water from external source.Cooling water circuit: Cold water is circulated in tubes in the condenser. The exhaust steam from the turbine flows into the condenser and leaves its heat to the circulating water. The cold water absorbs heat from the condensing steam and gets hot. This hot water is cooled with the help of cooling towers.Advantages of Thermal power plants

1. Can be located very conveniently near the load centre.2. Require less space as compared to hydro-electric plants3. Cheaper in production cost in comparison with that of diesel power stations.4. Cheaper in initial cost in comparison with that of diesel power stations.

Limitations1. Maintenance and operating costs are high.2. The plant efficiency decreases rapidly below about 75 per cent load.3. Pollution is high4. Fuel transportation and handling are difficult

Nuclear power plantIn nuclear power plant, heat energy available from nuclear fission is used for the

generation of steam. Nuclear fission is a process in which a nucleus is split into two divisions releasing energy in the form of electromagnetic radiation and kinetic energy. The kinetic energy of fission products is converted to thermal energy when these nuclei collide with nearby atoms. Electromagnetic rays produced during fission are absorbed by the reactor, their energy being converted to heat. The heat produced by fission in the nuclear reactor is carried out of the reactor by coolant. This heat is used to generate steam. The pressurized steam is fed to a steam turbine which is connected to a generator. The mechanical power generated in turbine is converted into electrical power by the generator.Nuclear reactor

Fuel (that is, fissionable nuclei such as uranium-235 or plutonium-239), is contained in fuel rods in the reactor core. The fissionable nuclei are bombarded with neutrons and the nuclei split into lighter nuclei. Energy and neutrons are also released in the process. These neutrons can then be directed to bombard even more fissionable nuclei in the fuel. A chain reaction develops and energy production continues.

A gas or liquid functions as the coolant. The coolant prevents the overheating of the system. It flows around the reactor core and absorbs the heat energy produced by the fission reactions. This heat energy is then transferred to the heat exchanger for steam generation. The steam is used to drive turbines in electricity generation. Ideally, a coolant will not undergo a phase change in the reactor due to an increase in temperature. Phase changes require energy and will reduce the thermal efficiency of the reactor. Good coolants are also inert.

The neutrons that are produced as fission products are very energetic and so move very quickly. The moderator ensures that the neutrons are moving slow enough to be able to collide with the nuclei. Common moderators are light water (H2O), heavy water (D2O) and graphite. A good moderator is one whose atoms are similar in mass to neutrons so that when collisions occur between the two, energy will be efficiently transferred from the neutrons to the moderator material.

To ensure that the fission reaction does not explode out of control, control rods can be periodically inserted into the reactor core. These rods contain materials (such as cadmium, hafnium and boron) that absorb neutrons and thus limit the fission reaction rate.

The reactor core is shielded to prevent the release of harmful radioactive material to the environment

Two reactor systems commonly used for nuclear power generation arePressurised water reactor: The heat generated in the nuclear core of the reactor is removed by water (coolant) circulating at high pressure. The primary circuit consists of a reactor, pressuriser and a coolant pump. The heat is transferred from the primary system to the secondary system in a heat exchanger. In the heat exchanger (boiler), steam is generated in the secondary section, utilising the heat liberated from primary section. The secondary system consists of a steam turbine coupled to a generator, a condenser and condensate feed pump. The pressurized steam is fed to a steam turbine which is connected to a generator. The mechanical power generated in turbine is converted into electrical power by the generator. The steam after expansion in turbine is condensed and the feed water is again re-circulated to the heat exchanger. The water in the primary circuit becomes radioactive and hence the entire primary circuit is shielded to protect operating persons.

Boiling water reactor: The heat released in the reactor is directly used for steam generation. The fuel used is enriched uranium oxide. The pressurized steam is fed to a steam turbine which is connected to a generator. The mechanical power generated in turbine is converted into electrical power by the generator. The steam after expansion in turbine is condensed and the feed water is again re-circulated.

Advantages of nuclear power plant1. Nuclear plant occupies less space than steam power plants. 2. A nuclear power plant consumes very small quantity of fuel. Thus fuel transportation cost is

less and large fuel storage facilities are not needed.3. The operation of a nuclear power plant is more reliable.4. Nuclear power plants are well suited to meet large power demands.5. Materials expenditure on metal structures, piping, storage mechanisms are much lower for a

nuclear power plant than a thermal power plantLimitations1. Higher capital cost2. Danger of nuclear radiation3. Problem of disposing the radioactive waste materials4. These plants cannot be operated at varying load efficiently. 5. Restricted availability of fuel.