L30500 Analysis of the Effects of High-Voltage Direct-Current Transmission Systems on Buried Pipelines

The economics of high voltage direct current for long-distance transmission of electrical energy have been reported as very attractive, to the extent that several projects are in the making. Several reasons other than the savings in transmission costs, for example the exchange of peak power between time zones and seasonal zones, would permit utilities to save on plant investment for generating capacity while maintaining a high level of service. This report summarizes work on the initial phase of a study to determine the effects of high-voltage direct-current (H.V.D.C.) electric transmission lines on buried pipeline systems. Pipeline Research Council International, Inc. initiated this work in response to an anticipated threat posed by the Pacific Northwest-Southwest Intertie H.V.D.C. system now being designed (and other possible H.V.D.C. lines in the future) because of the announced plans to pass direct current through the earth. The objectives of the overall program are:(1) To determine the nature and magnitude of problems that will be created by the earth current from H.V.D.C. systems, and(2) To devise means of protecting pipelines from the effects of such currents. A computer program was written based on a mathematical model of a buried pipeline in the environment created by an H.V.D.C. system. Excellent agreement was obtained between computed soil potential gradients and measurements obtained during a field test of H.V.D.C. in Oregon. Reasonably good agreement was also obtained between measured pipe-to-soil potentials on the Pacific Lighting Gas Supply Company pipeline near Camino, California, and computed values during a field test of H.V.D.C. power transmission.