Investigations-of Ground Currents and Potentials Near EHV DC Installations

Two test circuits utilizing alternating current transmission lines for conduction of direct current between electrodes are described. The earth was used as the return path. Both circuits were from the Hoover Powerplant area, one southwest toward Baker and the other south toward Needles, Calif. Potential gradients near the proposed site of the Mead terminal of the Pacific Northwest-Pacific Southwest Intertie are discussed at length. Neutral currents in numerous transformer banks, both transient and steady state are reported. Oscillograms are included which show the effect of separation of dc electrode and ac ground mat. Some data are included from similar earlier tests and comparisons made as to ground resistivity, potential gradients, etc. Test currents were on the order of 400-500 amperes with occasional values in the 600 ampere range.