# Video: Understanding the Electric Current Produced by Turbines in a Hydroelectric Dam

What type of electric current do the turbines in a hydroelectric dam produce?

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### 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.