How do hydroelectric powerplants work?

Water flows from a dam or reservoir through a valve called a penstock that regulates the flow. It then passes through a spiral-shaped pipe to make the water spin. The spinning water makes a turbine turn. The turbine then powers an electrical generator while the water is released downstream.

To make the generator work properly the turbine must spin at a constant speed. Using a speed governor to open and close water gates surrounding the turbine does this. This controls the speed and volume of water flowing to the turbine.

It is also possible to turn off the flow of water altogether using an enormous valve, so that maintenance can occur.

The amount of electricity that can be produced by hydroelectricity generation depends on two things:

• the rate at which the water flows
• the head of water. This is the difference in height between the water in the dam or reservoir and the water below the turbine.