WEBVTT

00:00:06.689 --> 00:00:21.242
♪ [Soothing music] ♪

00:00:21.286 --> 00:00:24.667
The use of water
to produce electrical energy

00:00:24.727 --> 00:00:26.453
is an extraordinary invention

00:00:26.453 --> 00:00:28.796
made possible by
gravity power plants.

00:00:29.908 --> 00:00:32.252
A hydroelectric plant
on the water

00:00:32.252 --> 00:00:36.139
produces renewable energy
from a river current.

00:00:37.518 --> 00:00:40.472
The hydroelectric plant
includes a dam,

00:00:40.622 --> 00:00:45.375
which allows water to accumulate
into a quasi-reservoir.

00:00:45.405 --> 00:00:51.125
♪ [Soothing music] ♪

00:00:51.175 --> 00:00:54.515
The more the distance between
retained and open water is raised,

00:00:54.790 --> 00:00:57.811
the greater the potential energy.

00:00:58.845 --> 00:01:01.308
Retained water flows through
underground pipes,

00:01:01.394 --> 00:01:03.830
to be deposited on
the other side of the dam.

00:01:07.207 --> 00:01:08.282
A turbine,

00:01:08.282 --> 00:01:12.430
for instance a Kaplan turbine,
is integrated into the pipeline.

00:01:13.875 --> 00:01:17.862
It is fitted with a propeller wheel,
similar to a ship's propeller.

00:01:21.159 --> 00:01:23.566
The steering wheel has
orientating blades,

00:01:23.566 --> 00:01:26.776
which direct the water flow
towards the moving wheel blades,

00:01:26.776 --> 00:01:28.070
in an effective manner.

00:01:29.347 --> 00:01:33.131
The electric motor 
changes the blades' direction.

00:01:34.399 --> 00:01:35.776
Once set in motion,

00:01:35.776 --> 00:01:39.762
the turbine drives an electric
generator, which produces electricity.

00:01:43.620 --> 00:01:46.086
The change of the blades'
direction

00:01:46.086 --> 00:01:48.454
strives to achieve
a high degree of efficiency,

00:01:48.454 --> 00:01:52.598
avoiding the inconvenience
of fluctuating river water levels.

00:01:54.946 --> 00:01:57.286
The spiral cover accelerates
the water...

00:01:57.632 --> 00:02:01.773
then, the steering wheel blades
direct it toward the moving blades.

00:02:02.054 --> 00:02:05.541
As the water hits the blades,
the moving wheel drives the generator

00:02:05.541 --> 00:02:08.534
which transforms mechanical energy
into electrical energy.

00:02:09.596 --> 00:02:12.883
Here are the components of
a hydroelectric power plant

00:02:12.883 --> 00:02:14.738
to better explain
the operation.

00:02:14.980 --> 00:02:18.648
Several installations, and the generator,
are in the machine building.

00:02:19.128 --> 00:02:20.799
With some exceptions,

00:02:20.799 --> 00:02:23.578
a transformer raises the voltage
of the current produced,

00:02:23.587 --> 00:02:27.573
so it can be transported easier
through high voltage lines.

00:02:29.981 --> 00:02:34.443
In 1913, engineer Victor Kaplan
invented the Kaplan turbine

00:02:34.443 --> 00:02:37.372
which perfected the concept
of the Francis turbine.

00:02:39.151 --> 00:02:43.947
The efficiency of a Kaplan turbine
varies generally between 90 and 95 %.

00:02:44.624 --> 00:02:48.514
The cavitation phenomenon has been
a major problem, persisting to this day.

00:02:48.705 --> 00:02:52.422
However, today there are several solutions
against cavitation,

00:02:52.540 --> 00:02:54.775
to protect the blades
of the Kaplan turbines.