Analysis on the converter transformer Sympathetic Inrush

The sympathetic inrush of converter transformers in Ultra High Voltage (UHV) direct current (DC) is studied in this paper. The characteristic and production mechanism of sympathetic inrush of converter transformers is given according to a false trip event during the 12 pulse converter transformer charged in Puqiao UHVDC project. Using the sympathetic inrush method focused on the residual flux, two corresponding methods are put forward based on the detail study and proved by the field test result. The HVDC can operate better when these methods are utilized in future HVDC protection systems.