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CHAPTER IX 



ARMATURE REACTION IN DIRECT-CURRENT 

 MACHINES 



62. The Direct and Transverse Armature Reactions. Let 

 Fig. 42 represent the developed cross-section of a part of a direct - 

 current machine, either a generator or a motor. For the sake of 

 simplicity the brushes are shown making contact directly with the 

 armature conductors, omitting the commutator. Electrically 

 this is equvialent to the actual conditions, because the commutator 

 segments are soldered to the end-connections of the same conduc- 

 tors. The brushes are shifted by a distance d from the geometrical 

 neutral, to insure a satisfactory commutation; d being expressed 

 in centimeters, measured along the armature periphery, the same 

 as the pole-pitch r. 



The actual armature conductors and currents are replaced, for 

 each pole-pitch, by a current sheet, or belt, of the same strength* 

 Let, for instance, the pole-pitch be 40 cm., and let the machine 

 have 120 armature conductors per pole. If the current per 

 ductor is 100 amp., the total number of ampere-conductors per 

 pole is 12,000; the total current of the equivalent belt, which con- 

 sists of one wide conductor, must be 12,000 amp., or 300 amp. per 

 linear cm. of the pole-pitch. The latter value, or the number of 

 armature ampere-conductors per centimeter of periphery', is some- 

 times called the specific electric loading of t he machine. The mag- 

 netic action of t he equvialent current sheet on the magnetic flux of 

 the machine is practically the same as that of the actual armature 

 conductors, because in a direct-current machine the slots an 

 paratively numerous and small. The current in the cross-hat dud 

 belts is supposed to flow from the reader into the paper,aml thecur- 

 rent in the belts marked with dots toward the reader. Wit h t he 

 t ions of the flux and of the current shown in the figure, the 

 uons of rotation of the machine when workiim us a generator 

 and as a motor are those shown by the arrow-heads (see Art. 24). 



163 



