An elementary book on electricity and magnetism and their applications . would be like arranging(&) a lot of cells in series with Fig. 137. — Batteries (a) without and (6) an eqUa] numDer turnedwith an external circuit. so that they are opposedto the first group (Fig. 137 (a)); obviously no current wouldflow. But if we imagine the copper wires on the outer surface ofthe ring to be scraped bare, and if two metal or carbon blocksor brushes at the top and bottom rub on the wires as they pass,a current could be led out of the armature at one brush and,after passing through anexternal resistance, s
An elementary book on electricity and magnetism and their applications . would be like arranging(&) a lot of cells in series with Fig. 137. — Batteries (a) without and (6) an eqUa] numDer turnedwith an external circuit. so that they are opposedto the first group (Fig. 137 (a)); obviously no current wouldflow. But if we imagine the copper wires on the outer surface ofthe ring to be scraped bare, and if two metal or carbon blocksor brushes at the top and bottom rub on the wires as they pass,a current could be led out of the armature at one brush and,after passing through anexternal resistance, suchas a lamp, could be ledback to the armatureagain at the other this case the armaturecircuit is double, consist-ing of its two halves inparallel. The adding ofbrushes and the externalresistance to the Grammering is like adding an external circuit to the arrangement ofcells described above. This battery analogue for a Gramme-ring armature is shown in figure 137 (6). In the Gramme-ring arrangement there are at every instant. Fig. 138. RiiiK armature with com-mutator. DIRECT-CURRENT GENERATORS 205 the same number of active conductors in each half of the arma-ture circuit, and so the current delivered by the armature isnot only direct but also steady. In practice, however, it would be difficult to make a goodcontact directly with the wires of the armature, because thewires must be carefully insulated from each other and fromthe iron core, and so the various turns of wire, or groups ofturns, have branch wires which lead offto the commutator segments, as infigure 138. The commutator consists of c pper barsor segments which are arranged aroundthe shaft and insulated from each otherby thin plates of mica (Fig. 139), Toget a satisfactorily steady current thereshould be many segments in a commu-tator, so that the brushes may alwaysbe connected with the armature circuitin the most favorable way. The brushitself is generally a block of carbon orgraphite held in position by a b
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectmagnetism, bookyear19
