5-C] 



CIRCLE DIAGRAM. 



185 





15. Fig. 4 shows that, in a loaded transformer, the resultant 

 ampere turns are constant;' hence the flux is constant, so that 

 the counter-electromotive force 

 irrespective of load equals, the 

 impressed electromotive force. As 

 the load changes, the primary cur- 

 rent assumes such a value that the 

 resultant ampere turns remains 

 constant and this condition of 

 equilibrium is maintained. 



1 6. The primary electromotive 

 force, thus balanced by the 

 counter-electromotive force, is Ep. 

 Referring to Fig. 3, it will be 

 seen that the terminal impressed 

 electromotive force, E 19 is a little 

 greater (say one per cent, greater) 

 than EP, on account of the RJ^ 

 and XJi drops, due to primary FIG. 4. Diagram of ampere 

 resistance and to leakage react- turns ' the resultan t am P ere 



turns are constant. 



ance. 



17. The locus of the secondary current I 2 is the arc of a 

 circle (13). Hence the locus of the primary load current, 

 7 (2) in Fig. 3, is the arc of a circle. The total primary current, 

 /!, measured from O to P, follows this same locus. 



Some simplified diagrams will now be discussed. 



1 8. Representation of Transformer Circuits. From the 

 foregoing discussion, it will be seen that the circuits of a trans- 

 former may be represented as in Fig. 5, in which the resistance 

 and leakage reactance of the two windings are considered as 

 external to the transformer. Furthermore, the exciting cur- 

 rent, 7 , is considered as flowing in a shunt circuit, also external 

 to the transformer. This shunt circuit consists of two branches: 



