The Electrical Engineer; A Weekly Review of Theoretical and Applied Electricity Volume 6

The Electrical Engineer; A Weekly Review of Theoretical and Applied Electricity Volume 6

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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. 1887 edition. Excerpt: the wire may be about.001 to.0015 amperes per square mil or,00079 to.0012 per oircular mil' of crosssection of the bare wire, which is equal to about 1000 to 1500 amperes per square inch, or 1000 to 650 square mils per ampere, or 1300 to 850 circular mils per ampere. In magnet coils made of fine wire, as in shunt machines, the current density in amperes per square mil may be slightly higher than in coils of coarse wire, as in series machines. The size of the wire should, therefore, also be determined from the current in order to guard against heating, besides being calculated from the formula first given, in which it depends on the allowable resistance. Should these two values for the diameter differ, the larger of the two will have to be taken in order that both the resistance and the heating will not exceed the limits. But a rule of this kind in which the current is limited only by the cross-section of the wire, although very simple in its application, is not sufficiently general to be relied upon in all cases. While it will give fair results for similarly proportioned coils, not differing too much in the actual sizes, it is less reliable for coils whose proportions and dimensions differ very considerably from those from which the constants were taken, which were ordinary oval machine magnets, not too long, having a moderate depth of winding, and which were exposed to the air on all sides. A much more reliable rule, though less convenient and not as simple in its application, is based on the following considerations: The heat in a coil is developed by the watts or volt-amperes which are consumed in the coil itself; this is a constant and continuous supply of heat which would continue to accumulate and ultimately destroy the coil if...
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Product details

  • Paperback | 674 pages
  • 189 x 246 x 34mm | 1,184g
  • United States
  • English
  • black & white illustrations
  • 1236820959
  • 9781236820952