Henry and Hora's modern electricity; a practical working encyclopedia by Henry James

Author:Henry, James. [from old catalog] & Hora, Karel Jan, 1881- [from old catalog] joint author
Language: eng
Format: epub, pdf
Tags: Electrical engineering
Publisher: Chicago, Laird & Lee, inc.
Published: 1915-03-25T05:00:00+00:00

ELECTRICAL ENGINEERING

173

Fig. 58.

The Siemens alternating current dynamo (see fig. 58) has two opposing crowns of cylindrical electro-magnets, the face pole-pieces being of opposite polarity. The armature coils in fig. 58 are only indicated. The lines of force pass from pole to pole, straight across the armature space. The armature coils, in revolving, cut through a series of powerful fields, with the lines of force alternating in directions. The armature coils equal the fields in number, therefore they are equally active at any given moment. In the position shown in fig. 58 the coils are just opposite the bobbins, and the two halves of each coil are cutting lines of force all due to one pair of opposite magnets, and, therefore, ali in one direction. The two E. M. F.'s induced in the two halves of the coil neutralize each other. At this moment the reversal of the current

direction takes place. As the coil moves onward, the front half of each coil cuts less lines of force than the rear half, in ever increasing ratio until the coil arrives at a position midway between the two pole-pieces where the E. M. F. is a maximum, because at that instant every line of force cut by the coil is utilized, and the induced currents, flowing outward

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