S-C] 



CIRCLE DIAGRAM. 



181 



and proportional to the flux density B. The B-H curve is a 

 straight line, instead of the familiar hysteresis loop, and there is 

 no hysteresis loss. 



The current 7 , as shown in Fig. I, is in quadrature with the 

 electromotive force and is wattless. 



7. The flux <f> links with the secondary circuit and induces 

 in the secondary an electromotive force ES, lagging 90 behind 

 the flux. The instantaneous 

 value of the secondary electro- 

 motive force is s = S 2 (d<f>-r- 

 dt). It is seen that Es is ex- 

 actly opposite to EP in phase 

 and is equal to Ep, multiplied 

 by (S 2 + SJ. 



8. The flux < throughout 

 this discussion refers to the flux 

 which links with both primary 

 and secondary, and EP and ES 

 are the induced or flux voltages,* 

 proportional to <f>. In an ideal 

 transformer there is no other 

 flux, but in an actual trans- 

 former there is, in addition to 

 this main flux, a relatively small 

 local or leakage flux, which links 

 with the turns or part of the 

 turns of one winding only and 

 causes a reactance called leakage 

 reactance. On account of the drop due to leakage reactance and 

 the drop due to the resistance of the transformer windings, as 

 discussed later, the terminal voltages, E and E 2 , are slightly dif- 

 ferent from the flux voltages EP and Es. 



* (8a). Strictly speaking Ep is not the flux voltage but is equal and 

 opposite thereto. 



Core-loss 

 Component 



O -B 



Magnetising 

 Component 



FIG. 2. Open-circuit diagram for 

 a transformer with core loss, show- 

 ing the two components of exciting 

 current and the angle a ofhysteretic 

 advance. 



