Inhaltsangabe
This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1895 Excerpt: ...these conditions, the dynamo is liable to act as a motor, and instead of taking power from the engine, to drive the engine at the expense of power from the other generators. 188. The exercise of care in the operation of the brushes and commutators will generally greatly prolong their lives. The brushes should always be carefully set at the right relative positions to each other; exactly opposite each other in bipolar machines; at exact quadrants in quadripolar machines; at exact sextants in six-pole machines, and so on, and this setting can best be accomplished by counting the commutator bars between the points of the brushes. The pressure brought to bear on the brushes should be as light as is consistent with efficient contact. The contact between brush and brush holder should be clean, since imperfect contact, through oil or dirt in the circuit of the brushes, is very apt to produce undue resistance and heating. The commutator surface should be wiped occasionally to remove particles of copper-dust which might accumulate detrimentally. 189. Carbon brushes have come into extended use, in all but low tension generators, for the reason that they wear uniformly, are solid instead of laminated, lubricate the commutator instead of scratching it, and considerably reduce the effects of sparking, since the carbon is more apt to burn away in sparks than copper on the commutator. The resistance of such brushes is very high compared with copper, and this interferes with their employment for very large currents. Syllabus. The electrical activity of a machine is limited by three considerations. (1.) By excessive drop of pressure in the machine which prevents the delivery of the required pressure at the terminals. (2.) By an excessive heating of the machine, which, besid...
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