Dynamo-Electric Machinery Volume 1, PT. 1; A Manual for Students of Electrotechniques (Paperback)

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. 1904 Excerpt: ...lines of force in the narrow field between the armature and the pole-piece is being continually altered, then, even though the total amount of magnetism of the field-magnet remains unchanged, eddy-currents will be set up in the polepiece and will heat it. This is shown by Figs. 122 to 124, which represent the effect of a projecting tooth, such as that of a Pacinotti ring, in changing the distribution of the magnetism of the pole-piece. Figs. 125, 126 and 127 (corresponding respectively to Figs. 122, 123 and 124) show the eddy-currents, grouped in pairs of vortices. The strongest current flows between the vortices and is situated just below the projecting tooth, where the magnetism is most intense; it moves onward following the tooth. Fig. 127 shows what occurs during the final retreat of the tpoth from the pole-piece. These eddycurrents penetrate into the interior of the iron, although to no great depth. Clearly the greatest amount of such eddy-currents will be generated at that part of the pole-piece where the magnetic perturbations arc: greatest and most sudden. A glance Fig. 12a. Fig. 123. Fig. 124. Alteration Of Magnetic Field Due To Movement Of Mass Of Iron In Armature. at Figs. 125, 126 and 127 will at once tell us that this should be at the " forward" corner or "horn " of the pole-piece of the generating dynamo. As a matter of fact, when any dynamo Fig. 125. Fig. 126. Fig. 127. Eddy-currents Induced In Pole-pieces By Movement Of Masses Of Iron. which has horned pole-pieces (such as the Gramme) has been running for some time as a generator this is found to be the case. The "forward" horns a and c (i. e. those which point in the direction of the rotation) are found to be hot, whilst the "hindward " horns are foun...