Reactance of Transmission Lines With Ground Return

Abstract

In this paper there is presented an analysis of the circuit consisting of any number of line conductors in parallel with a return through the earth and any number of ground wires in parallel. In the development of this analysis certain assumptions have been made which tests indicate do not detract at all from the engineering usefulness of the result but which simplify the formulas very much. The general formulas resulting from this analysis are condensed in Table A-1. For the application of this method to the calculation of ground faults it is necessary to know what value of earth conductivity applies. Considerable data in regard to this for various localities have been collected and are given in Table C-2. For convenience in makihg the calculations curves are given for various values of the earth conductivity over the range as indicated by test and experience. These curves are given as Figs. C-2 and C-3. Occasionally preliminary calculations are made in which very approximate reactance valutes are used. In such cases a line reactance of 0.8 ohms per mi. is used, and a zero phase sequence reactance of 2.6 ohms per mi. could be used with the same degree of accuracy. With one ground wire the zero phase sequence reactance would be about 2.0 ohms per mi. and with two ground wires about 1.6 ohms per mi.