Excitation (magnetic)
Excitation is a process to create a magnetic field from electric current. This process is used in electric machines (generators or motors) whose rotor spins in a magnetic field. This magnetic field can come from a permanent magnet or field coils. In the case of electric machine with field coils, a current must flow to the coil to generate the magnetic field, so that the field coils can act as a "magnet", like in the case of electric machine with permanent magnet. The device in which excitation happens is called the exciter.
Excitation (magnetic) Media
A 100 kVA direct-driven power station AC alternator with a separate belt-driven exciter generator, date c. 1917
A field coil may be connected in shunt, in series, or in compound with the armature of a DC machine (motor or generator).
Alternator of 1930s diesel generating set, with excitation dynamo above
