Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . Fig. 351. -The Act of Commutation of anArmature Coil. At the instant shown coil B is short-circuited bythe brush. * Suppose that the brush in Fig. 351 had been made of copper instead of carbon, as isgenerally used, its resistance would have been less and a greater current would havecirculated around the short-circuited coil, increasing the self-induction and probablymelting a piece of the brush by the heat of the arc. ARMATURES. 365. Fig. 352.—Brushes Set Diametrically Opposite on th
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . Fig. 351. -The Act of Commutation of anArmature Coil. At the instant shown coil B is short-circuited bythe brush. * Suppose that the brush in Fig. 351 had been made of copper instead of carbon, as isgenerally used, its resistance would have been less and a greater current would havecirculated around the short-circuited coil, increasing the self-induction and probablymelting a piece of the brush by the heat of the arc. ARMATURES. 365. Fig. 352.—Brushes Set Diametrically Opposite on the Commutator of a Bipolar Dynamo. point, and the E. M. F. in them is higher, causing a greatercurrent to rise for the instant, which is noticed by an in-crease in sparking at the brushes. To find the neutral, ornon-sparking point of a dynamo, when it is running, the brushesare rocked backward or forward until the sparking practicallydisappears, or until a point isfound where it becomes aminimum. The tendency ofa dynamo to spark can beentirely eliminated if, inconstruction, the armatureis divided up into manycoils. Each coil will thenhave only a few number ofturns, which will keep theself-induction down, when,the induced E. M. F. will bevery small, as a small coilcan more nearly occupy theneutral point. The modern dynamo has been so perfectedthat the sparking has been entirely eliminated. Manydynamos, however, do spark at the brushes, but the faultlies in the manner of adjusting the brushes, etc., rather than in the machine itself. So
Size: 1970px × 1269px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1900, bookpublishernewyo, bookyear1901
