Underground/underwater pipelines are susceptible to corrosion from DC stray current originating from the operation of High Voltage Direct Current (HVDC) transmission systems. With increasing population growth and the demand for electrical power, HVDC transmission is an economical method of transporting electrical energy over long distances. There are two distinct types of HVDC transmission, monopolar and bipolar. Monopolar systems use the earth or preferably sea water as the return circuit, whereas bipolar systems only use the earth or sea water during electrical upsets or faults.
This paper will outline the effect of stray current that originates from an HVDC transmission system that runs parallel to and crosses a crude oil and natural gas pipeline system. Ground fault currents as high as 2800 amps have been recorded flowing into the ground electrode when the bipolar HVDC system reverts to monopolar operation during fault conditions or during scheduled maintenance.
Keywords: High Voltage Direct Current, HVDC, Monopolar, Bipolar, Interference, Interference Current, Fault Current, Imbalance Current, Stray Current, Intertie, Mercury Arc Valve Converters, Thyristor, Pipelines, Underground Utilities, Stray Current Mitigation Systems, Drainage, Current Drainage, Current Pickup, Current Discharge