Outage of a HVDC converter station caused by discharges and AC-flashovers and possible improvements

The authors examine how, after seven years of operation, in summertime, during bad weather conditions, the most serious flashover occured at a Chinese HVDC convertor station. Three sets of capacitive voltage transformers in the AC yard suffered flashover with damage of some of the sections and one set of capacitive voltage divider experienced a partial discharge even inside the AC yard. Additionally there was a flashover on the noise capacitor in the DC yard. Consequently one DC protection and 5 AC protections activated. A fault analysis is made according to the site investigations and recordings of the monitoring system of the station. Some preventive measures are also presented in this paper.