Economic voltage of long transmission lines

THERE has been a need of a rational method of determining the economic voltage for a proposed transmission line. This voltage has often been decided upon after making several lengthy cost estimates of lines at different operating voltages. It is the purpose of this paper to indicate a solution by an application of Kelvin's Law. While this law has certain limitations, of which the engineer must be aware, attention will be called to these at the proper time. Inasmuch as a choice of line conductor is generally limited to such standard sizes as are manufactured commercially, and a choice of voltage is limited in the same way, it is neither necessary nor advisable to find a solution which is accurate to any great degree of refinement. Capacity and skin effect are purposely ignored in obtaining the approximate solution. Such refinements can later be applied. The scope of this paper will be to present a rapid solution of the economic copper conductor as determined by Kelvin's Law, and using this as a stepping stone, the solution of the economic line voltage will be developed; the theory will then be extended to conductors other than copper. The principles given should be regarded as general, and should be supplemented by the use of good judgment in their application.