Electric Light and Power Giving the Result of Practical Experience in Central Station Work

Electric Light and Power Giving the Result of Practical Experience in Central Station Work

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1894 edition. Excerpt: ...pressure under a varying load. The reason of this is not far to seek. The higher the speed of a series machine the higher the E.M.F., since E.M.F. is proportional to speed. This is when keeping the current constant. When the speed of a shunt machine is increased, and the external current kept constant by inserting resistance, then the shunt current is greatly increased, and so the E.M.F. rises much more than what it would if the shunt or magnetising current were kept constant. It is thus seen that the effect of speed is not the same on a series machine as on a shunt, therefore if a compound dynamo be run at any other speed than what it is designed for, the two sets of coils will not regulate each other as they should do. The field magnets of alternate-current machines cannot be "excited" by using the alternating current, since the magnets would be continually magnetised and demagnetised; it is therefore necessary to employ a continuous current, and this can be done in two ways: first, by running a small continuous-current dynamo, called an "exciter," and using it simply for magnetising the field coils of the alternatecurrent machine; secondly, by leading, say, some coils of the armature to a "commutator " fixed on the shaft in front of the "collector "--the alternating current thus obtained from these coils being commutated into continuous currents, are then used to excite the magnets. In the first case the exciter is run at a constant speed, and so the magnetic field of the alternate-current machine remains constant in strength; in the second case, the exciting current coming from the armature may vary in value, and so promote self-regulation. Armature Winding. Armatures can be divided into three...show more

Product details

  • Paperback | 98 pages
  • 189 x 246 x 5mm | 191g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236744799
  • 9781236744791