. The street railway review . lIG. 7. Transmission Cables.— As by three phase transmission a miui-muni of copper transmits a given amount of power with a givenloss, tills Is the system wliicii has lieen generally adopted fortransmission. Where the feeders are placed underground, threeconductor cables are used, the tiirec conductors being separatelyinsulated and then sunounded by a lead sheatii. Formerlyrubber was the Insulation used for this purpose, but paper hascome rapidly to the front and at present paper insulation is pre-ferred by many to rubber. Paper docs not soften under heatlike rubb
. The street railway review . lIG. 7. Transmission Cables.— As by three phase transmission a miui-muni of copper transmits a given amount of power with a givenloss, tills Is the system wliicii has lieen generally adopted fortransmission. Where the feeders are placed underground, threeconductor cables are used, the tiirec conductors being separatelyinsulated and then sunounded by a lead sheatii. Formerlyrubber was the Insulation used for this purpose, but paper hascome rapidly to the front and at present paper insulation is pre-ferred by many to rubber. Paper docs not soften under heatlike rubber, and tlie cable has the advantage of being cheapertiinn rubber and of having a soiiiewiiat greater overload weak part of any cable is tlie joint, and great caie slinuld. KIG. 9 —DUCTS FOK UNDERGROUND CONDUIT. be taken in spUclDg to exclude all moisture. This Is especiallytrue of paper Insulated cables. In estimating tiie sizes of caiiles for carrying the high tensioncurrent it is usually necessary to ligure tlie cable for ampere car-rying capacity instead of for drop in voltage, as is customary inloug-distiince transmission. This is on account of the short transmission distances as compared witli tlic high transmission volt-age. The amperes per phase for three phase transmission may cable which it is advisable to install in an ordinary duct, is onein whicli each conductor has a ^o. OOUU section. Tables >;os. 1 aud 2 give data aud cost of rubber aud paperinsulated three-conductor, lead-covered cables with No. tW con-duclors, lor voltages ranging from o,W0 to 20,000. It will beotjservcd that above 10,000 volts lor rubber aud above 15,000 voltslor paper insulated cables, the cost increases so rapidly as almostto make these tiie limiting voltages for
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Keywords: ., book, bookcentury1800, bookdecade1890, booksubjectstreetrailroads
