Topic of the Month—Galvanic Anodes Control Induced Voltages On Pipe Lines

Well-coated transmission pipelines constructed on the same right-of-way or adjacent to electric power transmission lines can be subjected to induced voltages of considerable magnitude during lightning storms and when ground faults occur on the power line. These potentials can develop because the pipeline, a paralleling metallic conductor is in effect a single turn secondary of an air core transformer, the power transmission line acting as the primary. The magnitude of induced voltage varies with the length of exposure, fault current, separation of power line and pipeline and soil resistivity. With bare pipelines the secondary is effectively short- circuited by the pipeline-to-earth resistance and the induced voltage, being consumed by impedance drop, does not result in appreciable voltage-to-ground of the pipeline. On well-coated pipelines, however, the distributed resistance-to-earth is relatively high, the pipeline behaving much like an open-circuited secondary so that a substantial portion of the induced voltage appears as a...