Power stations
A
power station is an industrial facility for the generation of
electric power.
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. It
depends chiefly on which fuels are easily available and on the types
of technology that the power company has access to.
In
thermal power stations, mechanical power is produced by a heat engine
that transforms thermal energy, often from combustion of a fuel, into
rotational energy. Most thermal power stations produce steam, and
these are sometimes called steam power stations. Not all thermal
energy can be transformed into mechanical power, according to the
second law of thermodynamics. Therefore, there is always heat lost to
the environment. The efficiency of a steam turbine is limited by the
maximum temperature of the steam produced and is not directly a
function of the fuel used. For the same steam conditions, coal,
nuclear and gas power plants all have the same theoretical
efficiency.
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 fuelled power plants may also use a steam turbine
generator or in the case of natural gas fired plants may use a
combustion turbine. Solar thermal electric plants use sunlight to
boil water, which turns the generator. Steam turbine plants use the
dynamic pressure generated by expanding steam to turn the blades of a
turbine. Almost all large non-hydro plants use this system. About 80%
of all electric power produced in the world is by use of steam
turbines. Gas turbine plants use the dynamic pressure from flowing
gases (air and combustion products) to directly operate the turbine.
Natural-gas fuelled (and oil fueled) combustion turbine plants can
start rapidly and so are used to supply "peak" energy
during periods of high demand, though at higher cost than base-loaded
plants.
