Superpower Transmission Economies and Limitations of the Transmission System of Extraordinary Length

This paper is a study of the transmission of very large blocks of power for extraordinary distances and has for its purpose the bringing out of the major operating characteristics of such a system, the characteristics which it possesses which are different from those of shorter transmissions and the duties imposed upon generators, transformers, synchronous condensers, switches, etc., primarily as affecting their design. The paper defines a superpower transmission line as a line of great length in which the charging kilovolt-amperes per mile of length is of the same order of magnitude as the reactive kilovolt-amperes developed by the full-load line current passing through the reactance of the line and in which the resistance is small relative to the reactance. Such a line is adapted for economical transmission only for a fairly definite amount of load and any great increase or decrease below this point leads to poor economy or unstability. Since, however, the load appropriate to a given line depends upon the voltage, an appropriate line can be laid out for any reasonable amount of power to be transmitted. In order to secure a definite set of conditions to serve as a specification for determining the performance of generators, transformers etc., all applying consistently to the same system, a typical hypothethical transmission has been assumed, namely, a delivery of 400,000 kw. over a distance of 500 miles over four circuits 220,000-volt at each end.