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♪ [Soothing music] ♪

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The use of water
to produce electrical energy

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is an extraordinary invention

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made possible by
gravity power plants.

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A hydroelectric plant
on the water

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produces renewable energy
from a river current.

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The hydroelectric plant
includes a dam,

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which allows water to accumulate
into a quasi-reservoir.

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♪ [Soothing music] ♪

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The more the distance between
retained and open water is raised,

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the greater the potential energy.

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Retained water flows through
underground pipes,

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to be deposited on
the other side of the dam.

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A turbine,

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for instance a Kaplan turbine,
is integrated into the pipeline.

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It is fitted with a propeller wheel,
similar to a ship's propeller.

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The steering wheel has
orientating blades,

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which direct the water flow
towards the moving wheel blades,

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in an effective manner.

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The electric motor 
changes the blades' direction.

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Once set in motion,

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the turbine drives an electric
generator, which produces electricity.

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The change of the blades'
direction

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strives to achieve
a high degree of efficiency,

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avoiding the inconvenience
of fluctuating river water levels.

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The spiral cover accelerates
the water...

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then, the steering wheel blades
direct it toward the moving blades.

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As the water hits the blades,
the moving wheel drives the generator

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which transforms mechanical energy
into electrical energy.

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Here are the components of
a hydroelectric power plant

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to better explain
the operation.

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Several installations, and the generator,
are in the machine building.

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With some exceptions,

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a transformer raises the voltage
of the current produced,

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so it can be transported easier
through high voltage lines.

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In 1913, engineer Victor Kaplan
invented the Kaplan turbine

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which perfected the concept
of the Francis turbine.

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The efficiency of a Kaplan turbine
varies generally between 90 and 95 %.

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The cavitation phenomenon has been
a major problem, persisting to this day.

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However, today there are several solutions
against cavitation,

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to protect the blades
of the Kaplan turbines.