Switching and Switchgear

Switching and Switchgear

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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. 1922 edition. Excerpt: ...such as tin and lead and their alloys, are extensively employed for fuses. When such a fuse is on the point of melting, the temperature reached is not sufficient to cause risk of fire, or rapid corrosion of the metal. Copper can be used when the fuse is not required to " blow " until a considerable overload is reached, or if the metal is enclosed. If run at a current near the fusing point a high temperature is reached, and this not only gives rise to risk from fire, but the metal corrodes on exposure to the air. Corrosion naturally reduces the section of the metal, and so leads to premature fusing. As_ regards the relations between specific resistance, sectional area, current density. and the temperature reached in operation, the design of fuses is similar to that of other conductors, but on account of the high temperatures involved, the facilities for cooling have a much greater effect on the fusing current than they have on the carrying capacity of an ordinary conductor. When the fuse is called upon to act on a sudden overload, the heat capacity of the metal and its surroundings naturally have a great influence on the current at which the cut-out will operate. The heat capacity gives the effect of a time lag in operation, i.e. a fuse will carry considerably more than its normal amperage for a short period. Since this effect is concerned with quantity of heat, the time limit is inverse, i.e. the greater the current the shorter the time period during which it can be carried. This inverse time lag has useful employment in many instances. Open Fuses. The simplest form of fuse is a wire stretched between two terminals or binding blocks. This type is naturally very cheap and finds employment when the metal is inserted as a...show more

Product details

  • Paperback | 28 pages
  • 189 x 246 x 2mm | 68g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 123698174X
  • 9781236981745