GENERAL THEORY OF THE TRANSFORMER. 



249 



circuit (reactance X of secondary receiving circuit being zero) is 

 to change the resistance in the main circuit of Fig. 216 without 

 changing its reactance a>P. Therefore, for varying values of R, 

 the locus of the load current P in the primary coil of a transformer 

 is a circle, and the total primary current is the vector sum of I' 

 and the magnetizing current which flows through the shunt cir- 

 cuit g$ Y This current locus is shown in Fig. 217. The line 

 E' represents the constant primary voltage, the line M represents 



Circle diagram of transformer delivering current to non-inductive receiving circuit. Based 



on Fig. 216. 



Fig. 217. 



the constant magnetizing current, and the line /' drawn from the 

 point 0' to any point P on the circular locus represents a pos- 

 sible value of the load current in the primary coil. The diameter 

 O'D of the circle represents the current which E r would produce 

 in a circuit of reactance coP and of zero resistance, this diameter 

 therefore represents E' j(dP amperes. The total primary current 

 is of course the vector sum of M and /' and it is represented by 

 a line drawn from to P. This circle diagram is especially 

 useful in induction motor calculations. 



122. Calculation of transformer regulation. Given a trans- 

 former of which the leakage reactance o>P, the coil resistances R f 

 and R", and the primary and secondary turns N r and N n are 

 known. The transformer is operated with a constant primary 





