FIND OUT MORE. Circuits 184–185 • Electricity 182 • Engines 198–199
Science and Technology^187
Electricity has revolutionized the way we use energy. It
can be generated in large. POWER STATIONS far away
from towns and cities, and distributed cleanly to homes,
offices, and factories through a network of power lines.
HOW DOES ELECTRICITY GET FROM THE POWER STATION TO US?
Electricity from a power station is boosted from 25,000 volts to 400,000 volts to
travel along power lines. But the voltage must be lowered before it is safe to use.
Transformers reduce the voltage in stages to different levels to supply factories,
railways, farms, hospitals, offices, homes, and motorways.
HOW ARE MOST GENERATORS POWERED?
To make electricity, the coils inside a generator are
turned by turbines. Most large generators are powered
by turbines spun around by high-pressure steam. The
steam is produced in boilers heated by fossil fuels (or
in a nuclear reactor). Water turbines are also used to
turn the generators in hydroelectric power stations.
WHAT IS ALTERNATING CURRENT?
Current is produced in two forms: direct current (DC)
and alternating current (AC). Direct current (produced
by batteries) only flows in one direction. Alternating
current (produced by power stations) switches back
and forth, reversing direction regularly. An AC current
switches back and forth 50 or 60 times a second.
WHAT IS THE NATIONAL GRID?
From the power stations, electricity is fed into a vast
network of cables and wires called the national grid.
Electricity travels through the grid into almost every
room in the country. Controlling the power in the grid
is complex. Engineers must try to make sure that
enough power is available whenever it is needed.
Power stations work day and night to produce the electricity that
provides us with heat and light, and drives all kinds of machines,
from hairdryers and refrigerators to televisions and trains.
POWER LINES
Electric current is carried
around the country by power
lines. Most power lines are
slung high above the ground,
on tall metal pylons. In towns
or cities, the lines may go
underground. Power lines
carry electricity at 400,000
volts – thousands of times
greater than the voltage
received in our homes.NATIONAL GRID 3
Electricity generated by the
power stations is fed into a
national grid of interconnecting
power lines. These take the
energy wherever it is required.
When you switch on a light, you
have no way of knowing which
power station the electricity
came from.Electricity Supply
HOMES
Electric power travels from
sub stations to homes
through underground cables
or lightweight overhead lines.
For domestic use, voltage is
reduced to 110 or 240 volts.
Each house has its own meter
to record the amount of
electrical energy used.FACTORIES
Large industrial plants
such as this chemical
factory use tremendous
amounts of electrical energy.
Many have their own
dedicated power stations.1 NIGHT LIGHTS
This night-time satellite
photograph shows the artificial
light produced on Earth by electric
road and building lights. North
America, Europe, India, China,
and Japan are the most brightly
lit regions. Over time, this map will
change as countries increase – or
decrease – their electricity output.POWER STATIONS
POWER STATION
A large, coal-fired power
station like this may produce a
continuous flow of up to
1,000 MW (megawatts)
of electricity. That's enough
power to light 20 million light
bulbs, or meet all the power
needs of a small city.SUB STATION
At various stages along the
way, the power lines feed into
sub stations. These contain
transformers and heavy-duty
switching gear that reduce
(lower) the voltage to safer
levels and direct power to
where it is needed.ENERGY EVERYWHERE
electricity
supply