Generators in power systems are almost synchronous
generators with few exceptions, for examples, induction
generators. The principle of generators is based on the
Fleming’s right hand law: e ¼ lv B, where e: electric
motive force, l: length of conductor, v: speed of conductor
and B: magnetic induction. Then generators
consist of field windings for generating magnetic induction
and armature windings for obtaining electric
power. For transforming rotating torque into electric
power, they almost consist of cylindrical rotor with field winding and cylindrical stater with armature winding.
The output power p is obtained as p ¼ k0D2lN, where k0
is called output coefficient, D is a diameter of air-gap
between rotor and stater, l is length of air-gap, that is,
length of armature conductor, and N is rotor-speed. The
output coefficient k0 is given as k0 ¼ k1BgAC, where k1 is
coefficient, Bg is magnetic induction in air-gap, and AC
is ampere-conductor per length of circumference of airgap.
The magnetic induction Bg is limited due to magnetic
saturation of material.