Three-Phase Transmission; A Practical Treatise on the Economic Conditions Governing the Transmission of Electric Energy by Underground and Overhead Conductors

Three-Phase Transmission; A Practical Treatise on the Economic Conditions Governing the Transmission of Electric Energy by Underground and Overhead Conductors

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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. 1911 edition. Excerpt: ...we have an induction motor with one pair of poles. The speed of the rotating field is, therefore, equal to the frequency or/revolutions per second. It would, however, be oscillating in character, and therefore have no effective torque upon the disc if it were not for the shaded poles. The effect of the copper pole-pieces is to retard the magnetism of this portion of the pole-pieces, so o o o o o U CO W--that the resultant effect is that of a tuft of magnetism sweeping across the face of the pole-pieces, and dragging the copper disc with it. It is specially to be noted that the limiting speed which could be attained by the disc would be f revolutions per second, less the slip required to generate sufficient eddy currents in the disc to overcome the retarding forces of the suspended weight and brake magnet. Now in the case of short circuits heavy currents will pass through the relay magnet. A powerful torque will thus be exerted on the disc momentarily, and it will immediately speed up to reduce the slip. How quickly and nearly the disc approaches synchronous speed will depend upon the extent of the short circuit current, the inertia of the disc and the retarding forces of the weight and permanent magnet. Having reviewed the function of the relay itself it becomes of importance to note some special features in the grouping of such apparatus upon switchboards usually carried out. It may be readily shown that complete protection will only be ensured by installing a separate current transformer upon each phase in circuit with a separate relay. The arrangement shown in Fig. 24 is sometimes adopted; two current transformers only cross connected being employed in combination with a single relay. This arrangement possesses the following...show more

Product details

  • Paperback | 44 pages
  • 189 x 246 x 2mm | 95g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 123675817X
  • 9781236758170