A hydroelectric power station converts the
kinetic, or movement, energy in flowing or falling water into electrical
energy that can be used in homes and businesses. Hydroelectric power
can be generated on a small scale with a ‘run-of-river’ installation,
which uses naturally flowing river water to turn one or more turbines,
or on a large scale with a hydroelectric dam.
A hydroelectric dam straddles a river, blocking
the water’s progress downstream. Water collects on the upstream side of
the dam, forming an artificial lake known as a reservoir (1). Damming
the river converts the water’s kinetic energy into potential energy: the
reservoir becomes a sort of battery, storing energy that can be
released a little at a time. As well as being a source of energy, some
reservoirs are used as boating lakes or drinking water supplies.
The reservoir’s potential energy is converted
back into kinetic energy by opening underwater gates, or intakes (2), in
the dam. When an intake opens, the immense weight of the reservoir
forces water through a channel called the penstock (3) towards a
turbine. The water rushes past the turbine, hitting its blades and
causing it to spin, converting some of the water’s kinetic energy into
mechanical energy. The water then finally flows out of the dam and
continues its journey downstream.
A shaft connects the turbine to a generator (4),
so when the turbine spins, so does the generator. The generator uses an
electromagnetic field to convert this mechanical energy into electrical
energy.
As long as there is plenty of water in the
reservoir, a hydroelectric dam can respond quickly to changes in demand
for electricity. Opening and closing the intakes directly controls the
amount of water flowing through the penstock, which determines the
amount of electricity the dam is generating.
The turbine and generator are located in the
dam’s power house (5), which also houses a transformer. The transformer
converts the electrical energy from the generator to a high voltage. The
national grid uses high voltages to transmit electricity
efficiently through the power lines (6) to the homes and businesses that
need it (7). Here, other transformers reduce the voltage back down to a
usable level.
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