Synopsis
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. 1908 Excerpt: ... methods are resorted to by most designers. LEAKAGE IN THE MAGNETIC CIRCUIT. The flux entering the armature is, of course, always less than the flux; existing in the poles and yoke of the machine, owing to the existence of / leakage lines which do not cut the conductors on the armature. Fig. 374 gives a good idea of the leakage lines in a bipolar machine. The whole of the flux generated in the field does not pass through the armature, for some of the lines from the field form local closed circuits, the flux composing these local circuits never entering the armature. In the old types of dynamo in which very long air gaps were employed, rendered necesssary by the use of surface wound (smooth core) armatures, the leakage was often very considerable, but nowadays, with the universal adoption of slot wound armatures and short air gaps (for economy in field copper) the leakage is much smaller. In the older machine the leakage co-efficient, defined as total flux generated useful flux in armature, was often i-; or more, whereas in modern continuous current machines, even in small sizes, the value seldom approaches this. The adoption of multipolar machines, except for very small motors of one or two horse power has also tended to decrease the leakage, and generally we may say that in a large multipolar machine the leakage coefficient will vary from ro8 to ri2, and in the four-pole machine will not exceed 1-15. In the smallest bipolar sizes the value should not exceed rz. In alternators, owing to the employment of FIG. 374.--LEAKAGE FIELD OF IRON-CLAD DYNAMO. generally longer air gaps, the values will range from r2 to 13. In Chapter III. the calculation for the magnetic circuit of a six-pole continuous current generator is given in detail together with the saturation...
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