Voltage Impact on Oil Pipelines from High Voltage Underground Cables: Relocation of Overhead Lines at Kelanitissa

When a large-scale urban construction project requires the relocation of an electrical overhead transmission line, going underground becomes the only feasible solution. However, due consideration must be given to the interaction with underground steel pipelines already laid as the life of metallic pipelines is highly susceptible to corrosion when buried underground. Corrosion occurs because of an electrochemical reaction, with Impressed Current Cathodic protection, with an impressed negative dc voltage of the order of 850 mV, usually employed in many metal pipelines to mitigate the deterioration of the surface. This paper scrutinizes the impact of high voltage underground cables on the cathodic protection of buried metal pipelines. The induced voltage due to the addition of high voltage underground cables crossing the pipelines perpendicularly has been analysed using Ansys Maxwell's electromagnetic software using actual dimensions and parameters. The introduction of two 220 kV underground cables from Biyagama - Kelanitissa line and two 132 kV underground cable circuits from Kelanitissa - Kolonnawa running perpendicular to six underground petroleum carrying steel pipelines has been investigated to study its influence on existing impressed current cathodic protection. The study has shown that the maximum induced voltage is less than 1.5 mV which has no adverse effect on any existing impressed current cathodic protection. The high voltage cables have been in fact installed and no adverse effects have been detected.