Skin Effect Current Tracing

A comparison of installed costs for resistance, impedance, and skin effect current tracing systems for a 20-in 4-mi long line shows a definite advantage for the skin effect system. This system depends on the fact that alternating current flowing longitudinally in a steel tube can be caused to concentrate near the inner wall by including the return conductor within the tube. With proper design there will be an absence of voltage on the outer tube surface, which can, therefore, be welded to a pipeline without disturbance of the ac circuit. The heat generated by the current flow in the steel tube will readily transfer to the pipe through the welds. Suitable parameter selection will result in economically practical voltage and current values, and will allow long lengths of pipeline to be heated from a single electrical power feed connection.