Can someone explain to me how exactly a hydroelectric generator works?

Question

I'm looking for details, not just the water goes in and electricity comes out.

Answer 1

Any generator works by turning a magnet within coils of wire.  The moving magnet cause a change in the magnetic flux in the wires, which induces a current:  i = dB/dt.  The force that turns the magnet can come from many sources: an internal combustion engine, a gas turbine, a windmill, a steam turbine (fired by coal, oil, or nuclear energy), or falling water, in the case of the hydroelectric generator.

A dam stops a river, causing a relatively deep reservoir to form.  This depth causes a static pressure to develop, which is basically a form of potential energy.  The pressurized water is forced through a nozzle onto a water turbine, causing that turbine to turn, providing the motive force for the magnet described above.

Answer 2

Falling water turns a turbine, Kind of like a horizontal water wheel. The wheel turns an electric generator which produces the electricity. A small household generator uses a gasoline engine to turn the generator. The water is "free". Here's a simple picture: