Video Transcript
What type of electric current do
the turbines in a hydroelectric dam produce?
Okay, to answer this question, we
will want to know a bit about how the turbines in a hydroelectric dam work. The basic idea with a hydroelectric
dam is if we start with a flow of water, say, a river flowing along, then we want to
block that flow, using a barrier that’s called a dam. When we do this, water starts to
pile up behind the barrier. It forms a pool that’s called a
reservoir. We can design the dam so that the
only way for water to go from the reservoir to the riverbed is to pass through the
dam in a particular channel. And then right in the middle of
that channel, we put what’s called a turbine.
A turbine is a device with angled
fins so that when water falls through it, the turbine starts to rotate. As the turbine rotates, so does the
shaft that connects the turbine to what’s called a generator. This is where the electrical energy
in this hydroelectric dam is actually produced.
The amount of electricity produced
by the generator depends on the particular angle of the rotating shaft. And we know that angle is
constantly changing, since the shaft is constantly turning. So sometimes, the electricity
produced is at a high point and then a little while later at a low point. But then, as the shaft continues to
rotate, the production goes back to a high point, and so on and so forth. The electrical current that the
generator produces goes up and down in a regular pattern. And not only that, but half of the
time, the current is moving in one direction. And the other half of the time,
it’s moving in the reverse direction.
The current generated above this
dotted line we could consider positive and the current below it, we could consider
negative, which just means it’s moving the opposite way. All this shows us that the
particular type of electrical current generated by a turbine is an alternating
current. This is electrical current that
regularly — periodically — changes direction. So that’s the answer to our
question.
