86 



THE MAGNETIC CIRCUIT 



[ART. 35 



In direct-current machines and in synchronous generators, 

 motors, and rotary converters, the magnetic flux (Figs. 15 and 20) 

 from a field pole passes into the air-gap and the armature teeth. 

 In the armature core the flux is divided into two halves, each half 

 going to one of the adjacent poles. The magnetic paths are com- 

 pleted through the field frame. Part of the flux passes directly 

 from one pole to the two adjacent poles through the air, without 

 going through the armature. This part of the flux is known as 

 the leakage flux. The closed magnetic paths and the field coils of a 

 machine may be thought of as the consecutive links of a closed 

 chain. While in a transformer the chain is open, in generators 



FIG. 23. The paths of the main flux and of the leakage fluxes in an 

 induction motor (or generator) . 



and motors the chain must be closed on account of the continuous 

 rotation. 



In induction machines, both generators and motors (Fig. 23), 

 the flux at no load is produced by the currents in the stator wind- 

 ings only. When the machine is loaded, the flux is produced by 

 the combined action of the stator and rotor currents, the rotor cur- 

 rents opposing those in the stator, the same as in a transformer. 

 Therefore, the flux in the loaded machine may be regarded as the 

 resultant- of the following three component fluxes: The main or 

 useful flux, 0, which links with both the primary and the secondary 

 windings; the primary leakage flux, 1; which links with the stator 

 winding only; and the secondary leakage flux, $ 2 which is linked 

 with the rotor winding alone. The leakage fluxes not only do not 



