THE ARMATURE REACTIONS OF ALTERNATORS 267 



To sum up, the case of the single-phase alternator should then 

 be treated exactly by the same general formulae, the same construc- 

 tions, and the same diagrams as in the case of a polyphase alternator, 

 but under the condition of considerably increasing the stray flux 

 wsl, adding thereto a term representing the parasitic rotating in- 

 ductance. The coefficient a>s is thus replaced by & s-f-;w( -j 



values / and /' are calculated by the theoretical coefficient of poly- 

 phase machines (see p. 263) (taking into account the saturation of 

 the circuits by the values given to R and R', as has already been 

 seen above). In this manner a coefficient m of reduction will be 

 determined less than unity, the more or less marked suppression of 

 the parasitic rotating inductance by the Foucault currents induced 

 in the surrounding non-laminated metallic masses, and in some cases 

 in special damping circuits. 



Consequences from the Point of View of the Construction of 

 Alternators for Good Regulation. The theory and the calculation 

 for the reactances just as they have been above analyzed, lend them- 

 selves to the discussion of the construction of alternators much better 

 than the old methods. We will proceed to give a few examples of 

 such applications. 



(A) In so far as concerns the employment of short bobbins, (gener- 

 ally abandoned by reason of the disfavor thrown upon them by 

 windings of only three coils per field, which give terrible pulsations), 

 the winding of six short bobbins which I. have indicated (Fig. 13) 

 may be compared with the ordinary winding (Fig. 10) by means of 

 the coefficients calculated above. The relations between the K of 

 the two being the same as between the respective coefficients k of the 

 E.M.F., it is evident that the advantage of the short bobbins from 

 the point of view of reactions, involves a loss of E.M.F. in exactly the 

 same proportion. To re-establish the desired value of the latter, the 

 number of turns of the armature must either be increased, consequently 

 re-establishing the same reaction, or the flux density in the air-gap 

 must be increased, and consequently the ampere-turns of the field- 

 magnets as well as the losses by Foucault currents. The two windings 

 are therefore equivalent from the constructive standpoint when the 

 field-magnet flux occupies the entire polar pitch. However, short 

 bobbins may be treated more rationally by reducing the breadth of 

 the field-magnet flux to two-thirds of the field-magnet pitch in such a 

 manner that the flux shall be entirely utilized in the coil. Further 



