THE ARMATURE REACTIONS OF ALTERNATORS 247 



the relation which connects the ampere-turns to be produced by the 

 field-magnet with those utilized in the armature, we have similarly 



FT= function of ^. 



The total ampere-turns necessary to the emergence of the flux from 

 the field magnets will be determined as above (Fig. 4): let XQ" 

 represent the magnitude equal to Nili", to the scale of the new 

 figure; the distance OQ will evidently represent the ampere-turns 

 absorbed by the field alone; it is this length OQ which would in 

 general be corrected by taking account of the stray field Af\. The 

 method of correcting the stray fields indicated above may be em- 

 ployed; we will give further on another more nearly accurate already 

 suggested, moreover, by MM. Picou and Guilbert. 1 



Remark No. 2, upon the Subject of Diagram No. i. It is to 

 be observed that following the respective values of the reactive coeffi- 

 cients, both direct and transverse, the point C, the extremity of the 

 Available E.M.F. on open circuit, may be either above or below T. 



With an alternator of unsaturated field magnets, the two reactions 

 have coefficients nearly equal, and C may then coincide with T, when 

 they are equal. Ordinarily, the coefficient of distortion, K t , tends to 

 be reduced, as we shall see, by a reduction in the breadth of the poles, 

 while the coefficient K has the opposite tendency. It results from 

 this that C tends to be above T. But the saturation of the field magnets 

 lowers it the more as the saturation is greater; because this latter 

 augments but slightly the supplementary ampere-turns necessary to 

 compensate for those of the armature, but greatly diminishes the 

 variation of the voltage between open circuit and full load. C is, 

 therefore, in general below T, as represented in the diagrams. 



The same condition may be found even with saturation, with 

 certain types of alternators, such for example as that which was exhib- 

 ited in 1900, in Paris, by the firm Sautter-Harle. This machine, 

 developed along a plan, formerly patented by Professor E. Thomson, 

 of an iron rotor (inductor alternator), has a single armature, two 

 exciting field-windings, and a yoke closing the magnetic circuit through 



1 The diagram of the present figure is analogous to a diagram recently pub- 

 lished by M. E. Quilbert (loc. cit.); it differs, however, in that the line FE is 

 expressed as a function of the coefficient K t instead of the coefficient K, and 

 that the expression of dephasing <j> is thus presented as a function of the ampere- 

 turns. 



