2. Relationship between windings, emf and armature reaction

2.1 Vector composition of armature and field magnetomotive forces

It's worth recalling this composition, as it relates directly to the Potier diagram of an alternator with a constant, unsaturated air gap. This diagram is also used for machines with salient poles (§ 4.3 of [ ]). when only the excitation current is to be determined.

The following relations [D 3 520] give the fundamental terms of the magnetomotive forces (fmm) created by the inductor (index f ) and armature (index I ) under balanced load: