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ELECTRICAL MACHINERY 



having as many paths as there are poles, and the wave 

 wound armature always having two paths. It may be 

 that there is a greater e.m.f. induced in one path than in 

 another if the brushes are unequally spaced. But if the 

 several paths are in parallel and one path has a greater 

 e.m.f. than the others, then this path will force current to 

 flow through the others even though there is no load on the 

 outside circuit. 





FIG. 282. Brushes Unevenly Spaced; the Armature is Then Similar 

 to the Battery Circuit Shown in Sketch (6). 



Cause of the Sparking. Consider the case shown in 

 Fig. 282 (a) where the brushes A, B and C are correctly 

 spaced, 90 apart, but D is misplaced so that the distance 

 A-D is 80 and the distance D-C is 100. The paths A-B 

 and B-C generate the normal rated voltage of the machine 

 while the two paths A-D and D-C generate something less 

 than this value as there are less effective inductors in the 

 latter two quadrants than in the others. 



The electrical conditions in the armature are then the 

 same as those shown in Fig. 282 (6) in which figure the 

 cells A and B are supposed to develop a higher e.m.f. than 



