Phasor Diagram of a Loaded Alternator
Phasor Diagram of a Loaded Alternator:
Consider a Y-connected alternator supplying inductive load, the load p.f. angle being Φ. Fig. (i) shows the equivalent circuit of the alternator per phase. All quantities are per phase.
Fig. (ii) shows the phasor diagram of an alternator for the usual case of inductive load. The armature current Ia lags the terminal voltage V by p.f. angle Φ. The phasor sum of V and drops IaRa and IaXL gives the load induced voltage E. It is the induced e.m.f. after allowing for armature reaction. The phasor sum of E and IaXAR gives the no-load e.m.f. E0. The phasor diagram for unity and leading p.f. is left as an exercise for the reader. Note that in drawing the phasor diagram either the terminal voltage (V) or armature current (Ia) may be taken as the reference phasor.
Fig: (a) Unity p.f (b) lagging p.f (c) leading p.f