THE ARMATURE REACTIONS OF ALTERNATORS 249 



already employed moreover by MM. Bauch, Potier, Guilbert, and 

 Picou. 



For greater clearness of explanation I shall represent the char- 

 acteristics upon the same diagram, but, in practice, they would be 

 drawn upon separate figures. The curves are referred to the E.M.F's. 

 as common abscissae, and the ordinates of the two curves represent 

 respectively the ampere-turns for the passage of a given flux (cor- 

 responding to the E.M.F.) in the magnetic circuit, with or without 

 the field magnets. The difference of the ordinates equals then the 

 ampere-turns absorbed by the field magnet alone, in the absence of 

 stray magnetic fields. 



This assumed, we shall then construct, according to custom ,the 

 diagram of E.M.F.'s by adding to the voltage U at the terminals the 

 internal drop r'l, then the loss by stray magnetic fields AF. We 

 thus obtain the E.M.F. OF produced in the armature. We find upon 

 the characteristic of the armature the ampere-turns OF' corresponding 

 to this E.M.F., and we lay them off on OF' in the direction of OF. 



We may then observe that the distortion may be determined by 

 the comparison of the ampere-turns of distortion with the useful 

 ampere-turns in that part of the machine which does not include the 

 field-magnets; because, in the transverse reaction, the reluctance of 

 the pole pieces may be neglected in relation to that of the entrefer 

 and of the armature (especially that of the teeth), and consequently 

 attribute to the path of this reaction the same reluctance as in the path 

 of the useful flux outside the field magnets. The determination of the 

 angle <f> (Fig. i) will then be transformed into simply replacing the 

 self -inductance by the M.M.F.'s applied to the armature. The ampere- 



turns T?'T= ~- will be laid off in the direction perpendicular to 



V2 



7, and OT is joined; then from F' the perpendicular F'D is dropped, 

 which will be equal to the ampere-turns of distortion 



\/2 



The line OD will then represent the ampere-turns to be supplied by 

 the field-magnets at the point of emergence, the remainder DF' being 

 furnished by the armature itself. 



It remains to determine the total field-magnet ampere-turns corre- 

 sponding thereto, taking into account the reluctance of the stray flux 



