Research on the Corrosion Influence of the HVDC Earth Electrode on the Nearby Transmission Line Towers and the Towers' Protective Measures

When DC current flows through the earth,there will be potential difference among different positions of the ground.If the DC earth electrode site near the transmission corridor,the DC current will flow among the towers with different equipotential surfaces through the shielding wires,which would lead to the corrosion of the towers' earth electrode.Actual parameters of DC earth electrode in the Jinping-Sunan ±800 kV UHVDC Transmission Project and the nearest AC transmission line(Er Zi Ⅱ line) under construction are exmplified here,the electrical model of the DC earth electrode,transmission line,ground wire tower grounding body and corresponding soil model are built under CDEGS program in this paper.The DC current flowing through each tower and its distribution character are fully and systematically researched.According to the earth electrode design as the operation total number of years and the calculation result of current value from tower into the ground,under ratio of anode operation,the corrosion quantity of each tower and the total corrosion quantity of the transmission are obtained.Some conclutions can be gotten from the calcultion results: the erossion quantity will be more with the increase of the resistivity of the middle earth layer and decrease of the grounding resistance of the tower,and the total corridor quantity is not more than 594 kg.In the end,some protective measures for the towers are given such as insulation between shielding wires and tower,filling grounding conductor with coke.