TRANSFORMERS 



297 



secondary open, the exciting current which is only 10 per cent of 

 full-load current flows. Thus the open-circuit reactance of a 

 transformer is of the order of one hundred times the short-circuit 

 reactance. 



Fig. 273 corresponds to Fig. 267, but is drawn to different 

 scales in order to show the relation between the various fluxes. 



E'P 



FIG. 273. 



2 = leakage flux surrounding the secondary winding; 



it induces in the secondary an e.m.f. equal and op- 



posite to E z " = jIzXz. 



= $ + ^ = total flux threading the secondary wind- 



ing; it induces in the secondary an e.m.f. E s in 



quadrature ahead of $,. 



= actual e.m.f. induced in the secondary E S = E -f E 2 '. 



I = leakage flux surrounding the primary winding; 



it induces in the primary an e.m.f. equal and opposite 



OEs = 



Of> p = $ p = $-(- $ LI = total flux threading the primary wind- 

 ing; it induces in the primary an e.m.f. Ep in 

 quadrature ahead of <?. 



OE P = E P actual e.m.f. induced in the primary. 



OEp r = Ep = component of impressed e.m.f. required to over- 

 come Ef, E P f =-E P = E l - #/. 



181. Vector Equations of the Transformer. The following 

 equations show the relations between the various e.m.f.'s and 

 currents in the transformer. 



