AC Machines | Describe the effect of armature reaction on the performance of alternator.

Effect of Armature Reaction on the Performance of Alternator: 

Armature reaction is the effect of the armature current flux on the main flux and hence the induced emf and further the terminal voltage. The armature reaction affects the alternator terminal voltage by influencing the main flux due to which the terminal voltage changes as the load pf changes. This leads to variation in the alternator voltage regulation even though the armature (load) current is constant. The flux due to the armature current affects the main flux depending on the nature of the load current (that is the pf).

At unity pf loads:

The armature current being in phase with the voltage while the main flux is differing in phase by 90 degree with the voltage. Thus the effect of the armature reaction is to cross magnetize and distort the main flux. 

At zero pf loads:

This effect is either opposing or adding directly to the main flux.

Zero pf lag: (demagnetizing effect) 

Zero pf lead:

(magnetizing effect: increase in magnetism)

For all other PF the effect is the combination of cross and (demagnetization or magnetization).