Ques. What is the relation between the cross sectional area of the conductors and the voltage?
Ans. For a given circuit, the cross sectional area of the conductors, or weight varies inversely as the voltage.
Fig. 2,192.—General Electric standard tower under construction.
Ques. Would the highest possible voltage then be used for a transmission line?
Ans. The most economical voltage depends on the length of the line and the cost of apparatus.
For instance, alternators, transformers, insulation and circuit control and lightning protection devices become expensive when manufactured for very high pressures. Hence if a very high pressure were used, it would involve that the transmission distance be great enough so that the extra cost of the high pressure apparatus would be offset by the saving in copper effected by using the high pressure.
In the case of the longest lines, from about 100 miles up, the saving in copper with the highest practicable voltage is so great that the increase in other expenses is rendered comparatively small.
In the shorter lines as those ranging in length from about one mile to 50 or 75 miles, the most suitable voltage must be determined in each individual case by a careful consideration of all the conditions involved. No fixed rule can be established for proper voltage based on the length, but the following table will serve as a guide: