Armature Reaction Of Alternator:
Definition:-In electrical machine, the main field is produced by field coils. In both the generating and motoring modes, the armature carries current and a magnetic field is established, which is called the armature flux.Armature reaction in a machine defined as the effect of armature magnetic filux on main magnetic flux.
There are three main fluxes associated with an alternator:
(i) Main useful flux linked with both field & armature winding.
(ii) Leakage flux linked only with armature winding.
(iii) Leakage flux linked only with field winding.
The useful flux which links with both windings is due to combined mmf of the armature winding and field winding. When the armature winding of an alternator carries current then an mmf sets in armature. This armature mmf reacts with field mmf producing the resultant flux, which differs from flux of field winding alone.
Armature reaction for different power factors :
(a) Unity Power Factor:-
The effect of armature reaction depends on nature of load (power factor of load). At no load condition, the armature has no reaction due to absence of armature flux. When armature delivers current at unity power factor load, then the resultant flux is displaced along the air gap towards the trailing pole tip. Under this condition, armature reaction has distorting effect on mmf wave as shown in Figure.
(b) Zero Power Factor Lagging:-
At zero lagging power factor loads the armature current is lagging by 90° with armature voltage. Under this condition, the position of armature conductor when inducing maximum emf is the center line of field mmf. Since there is no distortion but the two mmf are in opposition, the armature reaction is now purely demagnetizing as shown in Figure.
Phasor Diagrams
(c) Zero Power Factor Leading:-
Now at zero power factor leading, the armature current leads armature voltage by 90°. Under this condition, the mmf of armature as well as the field winding are in same phase and additive. The armature mmf has magnetizing effect due to leading armature current as shown in Figure.
Tags:armature reaction of alternator pdf ,armature reaction in ac machines,armature reaction in synchronous generator,armature reaction in alternator ppt,armature reaction in alternator animation,armature reaction in alternator at unity power factor wikipedia
