. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . generation, the mosteconomical investment in copper is twice as much as the amount that wouldbe indicated by the use of Kelvins law. Of course, the selling price ofelectrical energy per hp. is much more than three times the cost of itsgeneration in the majority of cases, but this example has been given toshow just how the comparison on this basis is directed. No account hasbeen taken of the fixed and varia
. American hydroelectric practice; a compilation of useful data and information on the design, construction and operation of hydroelectric systems, from the penstocks to distribution lines . generation, the mosteconomical investment in copper is twice as much as the amount that wouldbe indicated by the use of Kelvins law. Of course, the selling price ofelectrical energy per hp. is much more than three times the cost of itsgeneration in the majority of cases, but this example has been given toshow just how the comparison on this basis is directed. No account hasbeen taken of the fixed and variable costs of such items as poles, towers,insulators, insulator-supports, etc., as these should at all times be considered 276 HYDROELECTRIC PRACTICE separately. Any practical variation in the line (size of conductor) will not^generally speaking, have any effect on these costs. Thus, from the abov-eit would seem that the law laid down by the late Lord Kelvin (Sir WilhamThompson) would be better expressed in the form: When the total cost ofconductor in the line is equal to the cost per to the company of theenergy wasted, the most economical conductor cross-section is 2 4 6 8 10 12 14 16 Actual Investment to the Apparent (Kelvins Law) Investment25 50 75 IW 125 150 175 200 225 250 Cost of Line Conductor in Per Cent Fig. 153.—Relation Between Copper Investment and Cost of Line Losses The use of this law as given in Fig. 153 is greatly aided by a set of curvesgiving amperes per phase in terms of line voltage and kilowatts such asshown in Fig. 154. Since the three-phase system of transmission and dis-tribution is so much in general use these curves should be of practicalvalue. They are based on the following formulae, P = V3EI Sindl = V3E SYSTEM OPERATION AND ECONOMICS 277 Ferranti Effect in Transmission Lines.—Very long transmission linesconnected to the supply service at the generating end but open-circuitedat the far off receiving end, tend to maintain a hig
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