284 



PRINCIPLES OF ELECTRICAL DESIGN 



electromotive force in the conductors. If this leakage slot flux 

 (in the neutral zone) were actually cut by the conductors, it 

 would generate a component of electromotive force lagging one- 

 quarter period behind the main component (on the assumption of 

 sine- wave form), and it can therefore conveniently be represented 

 in vector diagrams as if it were an electromotive force of self- 

 induction. The quantitative calculation of this electromotive 

 force will be considered in Art. 97. Although only brief 

 mention has been made of the leakage flux in slots other than 

 those in the neutral zone, it is not suggested that this flux is 

 negligible in amount; but the flux distribution under the pole 

 face, whatever may be its distortion, affects only the wave shape 

 (and form factor) of the generated electromotive force, and in no 

 way alters the average value of the developed voltage. The 

 difference between the total flux entering the armature teeth 

 from each pole face and the amount of the slot flux (or the 

 equivalent slot flux) in the neutral zone represents the flux 

 actually cut by all the conductors on the armature. 



96. Calculation of Slot Leakage Flux. The effect of slot in- 

 ductance being generally to reduce 1 the amount of the total air- 



FIG. 112. Flux entering teeth in neutral zone; showing effect of armature 

 current in producing slot leakage. 



gap flux which is actually cut by the conductors, the simplest 

 way to obtain a quantitative value for the slot reactance is to 

 calculate the total flux which leaks from tooth to tooth in the 

 neutral zone. Diagrams (A) and (B) in Fig. 112 indicate the 

 approximate paths of the magnetic lines in the neutral zone, (A) 

 when the current in the slot conductors is zero, and (B) when it 

 has an appreciable value. The amount of flux diverted from 

 the armature core into the leakage paths referred to may be 



1 Except in the case of a condenser load and leading current, in which 

 case the tendency would be to increase the total useful flux. 



