Thread: Magnetic Field of an electric generator.

In order to produce an electric current in an electric generator you must have first a magnetic field. So basically (wikipedia):
-The EMF generated is proportional to the rate of change of the magnetic flux-
So, my doubt is how these magnetic fields are first generated for instance in the electric generators of a dam and what order of magnitude are they typically?

Thank you very much for your answers.

The rotating magnetic field is produced by a coil on the rotor of the generator. The direct current which supplies the magnetizing current in this coil comes from another machine called an exciter.

http://www.whitbyhydro.on.ca/pdf/5.2.C_GenBasics.pdf

Hi Harold, thanks for your answer. But then, how does the exciter generates the current that drives the magnetizing coil in the first place?

The exciter can use permanent magnets to generate its required magnetic flux.

Another way to get the excitation current is to use the rectified output of the a-c generator. To get the initial excitation current you would use a battery to "flash the field" of the generator, then the battery can be disconnected once the generator is creating its own field current.

ahh, that pretty much answers my question, thanks again Harold.