principles of electricity generation were discovered by Michael
1831. He found
a bar magnet
through a wire coil generated electricity. Modern generators are
more complex, but the difference is mainly one of scale.
stations range in size from single wind driven devices to major
sites, employing many hundreds of staff, but what they are all doing is converting
one kind of energy into another. Different stations use
a variety of
energy sources but they all generate electricity in the same way.
to its essentials, a power station consists of just two major items.
there is a machine that generates electricity when its shaft is turned - the
generator. Secondly, there is some kind of engine to
turn the shaft.
The generated voltage can be up to 25,000 volts, which is transformed
higher voltage for transmission on the grid.
need to turn fast and continuously, and the most efficient type of
this is the
In the United Kingdom, most power stations use steam-driven turbines.
a power station generator, the equivalent of Faraday’s bar magnet is a
a coil energised by direct current to produce a magnetic field. This is
on the central rotating shaft, and is called the
rotor. Around the rotor is a series of coils called the
stator, in which the electrical voltage is generated by
magnetic field. Both rotor and stator may weigh several hundred tonnes.
rotor turns at 3000 revolutions per minute - 50 per second - to produce
alternating current with a frequency of 50 hertz (cycles per second).
generators typically produce 500 megawatts of power, the largest
to 700 megawatts - enough
to light seven million 100 watt bulbs!
diagram below shows how coal is used to drive a turbine. Firstly the
pulverised into a fine powder. Mixed with preheated air, the coal
fiercely to heat water in the boiler tubes. The steam emerging at the
top of the
boiler is returned to the furnace to be superheated. This increases its
before it is piped to the high-pressure cylinder of the steam turbine.
Superheated steam may be hot enough to make the steam pipe glow a dull
red – over
hot gases leaving the boiler on their way to the chimney are used to
both the air needed for combustion and the condensed water returning to
boiler (in the economiser).
is pulverised into dust
air blows coal dust into the furnace
dust burns like a gas and boils the water
steam drives the turbines
generator produces electricity
is cooled and converted into water by the condenser
warm water is cooled by air blowing through the tower
is recirculated to maximise use
modern boiler can burn over 260 tonnes an hour of pulverised coal.
such quantities is expensive; so many coal-fired power stations are
to coalfields. Some coastal stations have coal brought in by sea, but
power stations generally have to be supplied by train. These stations
own loop line (‘merry-go-round’), where special hopper wagons discharge
their coal load on the move, into bunkers beneath the rails.
the same reasons, most oil-fired power stations are near oil
refineries, or are
located on the coast or large estuaries. A typical 500 megawatt boiler
up to 2,750 tonnes of oil per day – over
115 tonnes per hour.
stations waste a lot of the energy in the fossil fuels they burn. The
only about 38% of it into electricity. Most of the
wasted energy is
heat – in the flue gases, and in the water used to condense the steam
leaves the turbine cylinders. Combined
heat and power (CHP)
units make use of this ‘waste’ heat to provide hot water for room
The electricity generated can be used locally or supplied to the
Although many CHP schemes are currently being set up in Britain, the
are not always favourable, mainly because we have plenty of cheap
for home and industrial heating. It may be worthwhile for certain
users, such as
small factories and schools, leisure centres, hospitals and office
could become more important in the future, because it can help
reduce the emission of carbon dioxide –
a ‘greenhouse gas’ – into the atmosphere.
arrives in your area from the national supply network (the National
275,000 or 400,000 volts. It is reduced to 132,000 volts at a
distribution within each area of the country, travelling to further
known as grid
points. From these it is distributed on overhead lines
cables at 33,000 volts - the primary
distribution networks -
to the intermediate substations.
the intermediate substations, electricity at 33,000 volts is reduced to
volts for secondary distribution. The secondary
distribution networks then
carry it at 11,000 volts to individual towns, industrial areas and
heavy users such as manufacturing industries are supplied at 33,000
Electrified railways have their own substations which draw electricity
from the grid supply point - the latest overhead-line systems run at
the final substations, transformers reduce the 11,000 volt supply to
for small scale customers such as homes and shops. A typical substation
200 to 300 houses. Larger users such as farms take electricity at 415
Significant amounts of energy are used or
lost during extraction, processing, transportation, conversion and
distribution of energy.
The total energy efficiency of the natural gas is 90
percent, but electricity is only about 27 percent efficient.