AIR-GAP FLUX DISTRIBUTION 



283 



yet tending to obscure the issue when considering the problem 

 of regulation, and standing in the way of a clear conception of 

 the flux distribution in the air gap. 



The effect of the current in the buried conductors will be under- 

 stood by comparing Figs. 110 and 111, where the dotted lines 

 indicate roughly the paths taken by the magnetic flux under 

 open-circuit conditions (Fig. 110) and under load conditions 

 (Fig. 111). In the first case, when no current flows in the arma- 

 ture conductors, the whole of the flux entering the tops of the 

 teeth passes into the armature core and is cut by all the conduc- 

 tors. In the second case the magnetomotive force due to the 



Direction of travel of poles 



Fia. 111. Flux entering armature of A.C. generator when the conductors 

 are carrying current. 



armature current diverts a certain amount of flux from tooth to 

 tooth, which since it does not enter the armature core is not cut 

 by all the conductors. This conception of the slot flux, as that 

 portion of the total flux leaving the pole shoe, which crosses the 

 air gap but does not enter the armature core below the teeth, 

 disposes of the difficulties encountered by many engineers when 

 faced with the necessity of calculating the slot inductance. It 

 is unnecessary to consider the leakage flux in the slots under the 

 pole face, but it is important to know the amount of flux in the 

 neutral zone, 1 which passes from tooth to tooth and generates no 



l By neutral zone is meant the space between poles on the armature 

 surface where the lines of magnetic flux are parallel to the direction of travel 

 of the conductors. 



