Let us consider transform
(Fig. 23) having primary and secondary windings of resistances R1 and R2 and reactance X1 and X2 respectively.
Fig. 23. An equivalent diagram of an actual transformer,
Impedance of primary winding, Z1 = R1 + jX1
Impedance of secondary winding, Z2 = R2 + jX2
The vector diagrams for different kinds of loads for such a transformer are shown in Fig. 24 (a, b, c). In these diagrams, vectors for resistive drops are drawn parallel to current vectors whereas reactive drops are drawn perpendicular to the current vectors. The angle ɸ1 between V1 and I1 gives the power factor angle of the transformer.
Fig. 24. (a) Unity p.f., (b) lagging p.f. and (c) leading p.f.