Study on the Damage of Cooling Water Pipes in UHVDC Thyristor Valve Based on Thermal Effect of Current

The leakage of S-type cooling water pipes near the grading electrodes has occurred frequently in the UHVDC converter station, which has been operated, leading to a forced power outage and replacement of water pipes. Based on the model of current thermal effect, this paper analyzes the influence of electrode line, that connected by S-type cooling water pipes and grading electrodes, on water pipe damage and the reasons for the damage. The structure of the thyristor valve is analyzed, and the simulation of current thermal effect and designed experiment are conducted to study the causes of water pipe damage. The research shows that the current applied to the grading electrode line should be much greater than that passed by the valve during the actual normal operation, to result in the PVDF water pipes achieving to the melting level by the heat of electrodes. Because the grading electrode wire connects busbar and the deionized water in the cooling water pipes, also there are other electrodes nearby that play the role of forcing potential, it is impossible for the grading electrodes to generate a large current. Therefore, other study models need to be considered for the damage mechanism of cooling water pipes.