Influence of Electromagnetic Field Generated by HVAC Transmission Lines on Nearby Underground Metal Pipelines

Abstract

High voltage AC (HVAC) power lines can induce significant amount of voltages on underground gas/oil metal pipelines in areas where they share similar Right of Way, the situation becoming more serious particularly in case of fault conditions. Electromagnetic field generated by the HVAC transmission lines on these gas/oil underground metal pipelines, generate unwanted voltages which present threats to personnel, the pipeline and its associated protective equipment such as cathodic systems. In cases where the induced voltages don’t meet the standards, the application of mitigation is necessarily compulsory to minimize these induced voltages to levels that are safe for personnel and the pipeline. This research studies the effect of electromagnetic field from a 500kV AC power line. A comprehensive interference analysis was performed on two different cases under steady state and fault condition using CDEGS software package. For the steady state condition, most of the results obtained are in agreement with GB 6830-1986 standard. However, due to high currents generated under single phase to ground short circuit, rising the potential of adjacent soil including the underground pipeline; induced voltages were found to be beyond the standard limits as stated in ITU-T DL/T 5033-2006. To provide a solution to this problem, two different type of mitigation systems are analyzed (the gradient control wire and earth electrode). After simulation, the proposed mitigation systems are found to greatly reduce the induced voltages on both studied cases under single phase to ground fault condition at different levels. However, the gradient control wire technique reduces these voltages to much lower voltage levels than earth electrodes, the former mitigation technique is suggested for the implementation to lessen the pipeline coating voltage stress to safe standard limits.