98 



SYNCHRONOUS MOTORS 



characteristic curve, or presenting unequal coefficients of direct and 

 transverse reactions. In the elementary theory it was assumed, on the 

 contrary, that the permeability of the field-circuit is practically constant 

 and that the two reaction-coefficients are equal. 



Particular Case where the Permeability of the Field-Circuit is 

 Constant and the Two Reaction-Coefficients are Equal. It is inter- 

 esting to note how, in this case, the new and more general diagram com- 

 prises the previous forms as a particular solution. It is only necessary, 

 indeed, to observe that the coefficient of transverse reaction, L', then 



FIG. 47. 



becomes equal to what we have termed the coefficient of mean self- 

 induction L. Likewise, the direct armature-reaction, which produces 



KN'I d counter-amperes-turns due to the reactive current, gives rise 



v 2 



to a counter E.M.F. which can be represented by ajLI d . Therefore, 

 between the effective E.M.F., 2 , and the open circuit E.M.F. obtained 

 with the; same excitation, we have the relation 



I d being always taken as positive on the right-hand side of BY and as 

 negative on the left-hand side. Suppose, for example, I d to be negative. 



