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. 1906 Excerpt: ...considerations of cost, and should not be used for large outputs except in special cases. Aside from the reasons dependent strictly upon the magnetic limit of output, it may be said that 2-circuit windings are more or less unsatisfactory whenever the output is so large as to require the use of more than two sets of ...
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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. 1906 Excerpt: ...considerations of cost, and should not be used for large outputs except in special cases. Aside from the reasons dependent strictly upon the magnetic limit of output, it may be said that 2-circuit windings are more or less unsatisfactory whenever the output is so large as to require the use of more than two sets of brushes (in order to keep the cost of the commutator and the "reactance voltage"--to be discussed later--within reasonable limits), because of the 2circuit windings lacking the property of compelling the equal subdivision of the current among all the sets of brushes used. Selective commutation occurs, one set of brushes carrying for a time a large part of the total current; this set of brushes becoming heated. This trouble is greater, the greater the number of sets of brushes, and the practicability of 2-circuit windings may be said to be inversely as the number of poles. If, however, in multiple-circuit windings the part of the winding opposite any one pole-piece should tend to take more than its share of the current, the increased armature demagnetisation and CR drop tends to restore equilibrium, this property constituting a great advantage. Voltage Per Commutator Segment As Related To Inductance As already stated, the average voltage between commutator segments, although it can be relied on to give good results if care is used in special cases, is not a true criterion of the inductance of a coil. For in different types, this expression may have the same value for coils of different inductances. Thus if the design is for an armature in which the conductors are located in holes beneath the surface, the inductance will be very high, and it would be necessary to limit the average voltage per commutator segment to a very low value. If the...
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