294 



ELECTRICAL ENGINEERING 



0$ = <J> = flux threading both primary and secondary wind- 

 ings in quadrature ahead of E b and E 2 . 



O/o = -To = primary exciting current leading the flux < by 

 an angle 90 6 , where is the primary power 

 factor at no load. 



Or = /' = primary load current in phase opposition to 7 2 , 



O/i = /i = total primary current. 



OE' = E' = component of primary impressed e.m.f. required 



to overcome the primary induced e.m.f. Eb. 

 OEi = EI = I\TI = e.m.f. consumed by primary resistance in 



phase with /i. 

 OEi" = EI" = jl&i = e.m.f. consumed by primary reactance 



in quadrature ahead of /i. 



EI" = IiZi = e.m.f. consumed by primary impedance. 

 EI = E f -f- EI" = primary impressed e.m.f. 

 angle of lag of the primary current behind the impressed 



e.m.f. Cos 0i = primary power factor. 



2 = angle of lag of the secondary current behind the second- 

 ary induced e.m.f. 



Fig. 268 shows the vector diagram of a transformer with a non- 

 inductive load and Fig. 269 with a capacity load of 50 per cent 

 power factor leading. 



OE,'" 

 OE lt 



0i 





FIG. 268. Vector diagram of a transformer with FIG. 269. Vector diagram of a 

 a non-inductive load. transformer with a load power 



factor of 50 per cent leading. 



179. Exciting Current. When a sine wave of e.m.f. is im- 

 pressed on the primary winding of a transformer, a sine wave of 

 flux must be produced linking with the primary winding. The 

 exciting current which produces thv ix cannot be a sine wave 



