92 SYNCHRONOUS MOTORS 



circles will be more or less deformed by these variations of reactance. 

 The saturation of the fields, for strong excitation-currents, reduces 

 these deformations and raises the right-hand branch of the V-curves 

 more rapidly toward the top than calculation would indicate. It is 

 generally admitted that there is no other way of taking these deforma- 

 tions into account than by plotting the V-curves experimentally. 



(3) No attention has been paid to the variation of losses in the 

 armature other than the resistance-loss. It may be remarked that these 

 losses will vary but little, since the friction is substantially constant, and, 

 in a motor supplied from a constant potential, the resultant E.M.F. in 

 the motor remains almost constant. Likewise the induction and the 

 hysteresis losses and the eddy currents remain approximately constant. 



The only variable losses are those due to eddy currents in the 

 fields, and the energy expended for excitation, neither of which have 

 been taken into consideration in what precedes. 



Practically, therefore, no great error has been made in supposing 

 the losses in the iron to be constant while increasing slightly the no- 

 load losses (by way of compensation). 



Attention is, therefore, called to this last source of imperfection 

 merely to show its influence. In reality, the same thing might also be 

 said in regard to the first two causes of imperfection, because the 

 true object of this theory is only to elucidate the general course of the 

 phenomena, and to give a method of calculation which will be sufficient 

 for practical purposes. However, the effects to which attention is 

 called above may assume sufficient importance, at times, to justify a 

 somewhat more detailed investigation. This is more especially true in 

 regard to variations of reactance. 



Variations of Reactance with Lag of Current and Saturation of 

 Fields. Armature-Reaction. The author has shown, elsewhere (L* In- 

 dustrie Electrique, 1899, p. 481) that the self-induction of any alternator 

 can be represented by two armature-reactions: 1 



(i) An armature-reaction directly opposed to the exciting ampere- 

 turns and which is equivalent to 



KN'I d 



counter-ampere-turns. In this equation 7j=the effective amperes 

 of reactive current, with respect to E%\ N' equals the number of arma- 

 ture conductors in the induced field; and K equals a coefficient which 



1 See Part II, Chapter I. 



