174 GENERAL DIAGRAMS FOR SYNCHRONOUS MOTORS 



Generalities. Reduction of all Armature-Reactions to the Single 

 Direct Reaction. The inducing field is the resultant of three magneto- 

 motive forces (Fig. i): 



1. The inducing ampere-turns of the exciting current; 



2. The ampere-turns which are reactive with respect to the E.M.F. 



and which act in the same way as the preceding; 



3. The difference between the active ampere-turns and the second- 



ary ampere-turns produced by the direct current. These 

 two kinds of ampere-turns tend to produce fields which are 

 diametrically opposed to each other and which make a phase- 



angle of with respect to the exciting field. 

 2 



Practically, the theory is greatly simplified by the fact that the 

 active ampere-turns and the direct-current secondary ampere-turns 

 are substantially equal to each other at all loads. 



On the one hand, the winding being a direct-current winding, the 

 average number of active ampere-turns will be given by the formula, 



N 

 K-I W V 2 , ........ (a) 



in which N= number of wires; 



l w = active component of primary alternating current; 

 K= reduction-coefficient due to the overlapping of the wind- 



ings, for an infinitely large number of slots. 



The author has published some average values for this coefficient. 

 It should, preferably, be determined from existing machines. 



On the other hand, the average number of ampere-turns due to 

 the direct current, Io, produced by the converter, is equal to the mean 

 value, 



2 2 



Dividing (b) by (a) we have the ratio of the secondary and primary 

 ampere-turns: 



Whatever may be the number of phases, q, if the efficiency be 

 assumed equal to unity, which makes the primary and secondary 



