♪ [Music] ♪

The use of water
to produce electrical energy

is an extraordinary invention

made possible by
gravity power plants.

A hydroelectric plant
on the water

produces renewable energy
from a river current.

The hydroelectric plant
includes a dam,

which allows water to accumulate
into a quasi-reservoir.

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

the greater the potential energy.

Retained water flows through
underground pipes,

to be deposited on
the other side of the dam.

A turbine,

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

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

The steering wheel has
Oriental blades,

which direct the water flow
towards the moving wheel blades,

in an effective manner.

The electric motor 
changes the blades' direction.

Once set in motion,

the turbine drives an electric
generator, which produces electricity.

The change of the blades'
direction

strives to achieve
a high degree of efficiency,

avoiding the inconvenience
of fluctuating river water levels.

The spiral cover accelerates
the water...

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

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

which transforms mechanical energy
into electrical energy.

Here are the components of
a hydroelectric power plant

to better explain
the operation.

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

With some exceptions,

a transformer raises the voltage
of the current produced,

so it can be transported easier
through high voltage lines.

In 1913, engineer Victor Kaplan
invented the Kaplan turbine

which perfected the concept
of the Francis turbine.

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

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

However, today there are several solutions
against cavitation,

to protect the blades
of the Kaplan turbines.