ELEMENTS OF ELECTRICAL ENGINEERING. 



Fig. 23. 



under the north poles are just balanced by the electromotive forces 

 induced under the south poles, as is shown diagrammatically 

 in Fig. 23. To utilize the induced electromotive forces e e e e e e, 

 Fig. 23, for the production of direct current, six brushes a a a 

 and b b b, Fig. 22, should be used. Three of these brushes 



maintain contact with the windings 

 at a a a, and through all three of 

 these brushes current flows out of 

 the armature to one terminal of a 

 receiving circuit. The other three 

 brushes bbb maintain contact with 

 the windings at bbb, Fig. 23 ; all 

 three of these brushes are connected 

 to the other terminal of the receiv- 

 ing circuit, and current flows into 

 the armature through all three. 

 The three brushes a a a together 

 constitute, therefore, the positive terminal of the armature, and 

 the brushes bbb constitute the negative terminal of the arma- 

 ture. 



Armature current and armature resistance. The total current 

 flowing out of the armature of the six-pole dynamo shown in Fig. 

 22 flows out of the three brushes a a a, so that one third of the 

 total current flows out of each of the positive brushes. An 

 inspection of Fig. 23 shows, furthermore, that current flows in 

 the armature winding to each positive brush from both sides ; 

 that is through two paths. Therefore, in the six -pole dynamo 

 with a simple ring armature, there are six paths (in parallel) in the 

 armature winding from negative to positive brushes, and therefore 

 one sixth of the current output of the machine flows through each 

 path. 



The resistance of this six-pole armature between positive and 

 negative brushes is equal to one sixth of the resistance of any one 

 path, since the six paths are similar and in parallel. Therefore 

 the resistance of the armature between positive and negative 



