SINGLE-PHASE KfOTORS 



287 



The principle of operation of such a motor is as follows: 

 Figure 264 (a) shows a gramme-ring armature and its commuta- 

 tor. This is the same type of armature as would be used for a 

 direct-current machine. This armature operates in a bi-polar 

 magnetic field, the field structure bring laminated. The fields 

 \cited by a winding connected directly to a single-phase 

 alternating-current line. At the instant shown, the upper wire 

 is positive and the current is increasing in a positive direction. 

 The flux \\hieh is substantially in phase with this current is also 

 increasing and by the corkscrew rule is directed upwards. This 

 flux divides, half going through each side of the ring armature. 



It is clear that the winding on each side of the ring armature 



Fio. 264. Currents and emfs. in th<> windings of a repulsion motor, brushes in 



geometrical neutnil. 



acts as the secondary of a transformer. Therefore, the alternat- 

 ing flux produced by the field winding, as primary, induces an 

 emf. in each half of the armature. By I.en/'s law, this induced 

 emf. has such a direction as to oppose the inducing flux. The 

 direction of this induced rinf. at the instant indicated in Fig. 264 

 BD by the arrows on the windings. It will be noted, by 

 following through the winding, that the resultant direction of 

 this induced emf, is ///;//v//v/ in each side of the armature. This 

 is indic.-ited diagram ma t i.-ally in 1 b), where the arrows 



show the general direction of these induced eniN. through the 

 armature. Were there no bru-ln>. it |fi .-vidrnt that no run-rut, 

 would flow if) the irmature winding, as the emf. in one-half of the 

 winding is equal and in phase opposition to that in the other half. 



