. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. Pig. —Allis-Chalmersbrush holder and sliprings. The latter aremade of cast copper,which the buildersclaim to be more satis-factory than cast some of the targelow speed machines thecollector rings are split,but on the majority ofalternators they are inone piece. Current is ledinto the rings by means■>f carbon brushes, thenumber of brushes be
. Hawkins electrical guide. Questions, answers & illustrations; a progressive course of study for engineers, electricians, students and those desiring to acquire a working knowledge of electricity and its applications; a practical treatise. Pig. —Allis-Chalmersbrush holder and sliprings. The latter aremade of cast copper,which the buildersclaim to be more satis-factory than cast some of the targelow speed machines thecollector rings are split,but on the majority ofalternators they are inone piece. Current is ledinto the rings by means■>f carbon brushes, thenumber of brushes be-ing such that the cur-rent density at the rub-bing contact is keptwithin At least twobrushes per ring areprovided, so that be removed for ir-•ion without inter-rupting the excitingcurrent. In larye ma-chines the brush holderstuds are mounted ona stand supported fromthe base;on small alter-nators they are usuallyfastened tc theone of the bearing ped-estals. CONSTRUCTION OF ALTERNATORS 1,203. Pig. 1,473.—Fort Wayne multi-phase revolving armature al-ternator, designed for use insmall power plants and isolatedlighting plants where inductiveloads are encountered. Builtfor pressures of 120, 240. 480,and 600 volts. These voltageshave been recommended by theAmerican Institute of Electri-cal Engineers, and will cover theneeds of any set of conditionsordinarily met with. Thesestandard voltages not only per-miteconomical distribution, butthey are such that no trans-formers are necessary to re-duce the line pressure for ordi-nary cases. For transrrittingpower relatively long distances,600volt,= is usually there is a demand for480 volt service, a 480 volt al-ternator should be selected andif lower voltages arealso desiredan auto-transformer may befurnished by means of which 240 volts can be obtained. When 120 volt circuits are necessarv for lighting, etc., the240 volt pressure can be still further reduced to 120 volts bv means of another au
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