Science Fair Project Encyclopedia
At the center of nearly all power stations is a generator, a rotating machine that converts mechanical energy into electrical energy by creating relative motion between a magnetic field and a conductor. The energy source harnessed to turn the generator varies widely from installation to installation.
In thermal power stations, mechanical power is produced by a heat engine, which transforms thermal energy, often from combustion of a fuel, into rotational energy. Not all thermal energy can be transformed to mechanical power, according to the second law of thermodynamics. Therefore, thermal power plants also produce low-temperature heat. If no use is found for the heat, it has to be rejected. If reject heat is employed as useful heat, for industrial processes or district heating, the power plant is referred to as a cogeneration power plant or CHP (combined heat-and-power) plant.
Thermal power plants are classified by the type of fuel and the type of prime mover installed. Nuclear power plants use a nuclear reactor's heat to operate a steam turbine generator. Fossil fueled power plants may also use a steam turbine generator. Natural gas fired plants may use a combustion turbine which provides rapid startup for peak loads. Combined cycle plants will have a gas turbine fired by natural gas or oil, with a steam boiler and steam turbine to improve the overall efficiency of the plant. A relatively small amount of electric power is produced by internal combustion piston engines. These are usually fuelled by diesel oil, heavy oil, natural gas or landfill gas. Piston engine plants are used to provide power for isolated communities or for emergency power for network failures.
Some thermal power stations are easily identified by their natural draft cooling towers, huge hyperbolic chimney-like structures that release the waste heat to the atmosphere. They may be employed at either nuclear or fossil fueled stations.
A pumped storage hydro power plant is a net consumer of energy but increases the value of electricity. Water is pumped to a high reservoir during the night when demand for electricity is low. During hours of peak demand, the stored water is released to produce electric power.
A solar photovoltaic power plant converts sunlight directly into electrical energy, which may need conversion to alternating current for transmission to users. This type of plant does not use rotating machines for energy conversion.
Most power stations are designed to generate AC power with three phases of 50 Hz or 60 Hz. In some power stations in Germany, Austria and Switzerland (traction powerstation) there is a second generator for single phase AC current with 16.7 Hz for the traction power network.
- Electricity generation - this article covers many topics that relate to power stations
- Electricity transmission
- Future energy development
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