Study on High Voltage Capacitor Unbalance Protection in HVDC Projects

To detect internal faults of capacitors, the HV capacitors in the filters of HVDC projects are H-connected or branch-connected, with capacitor unbalance protection as their primary protection. However, there are still some hidden problems in the criterions of the existent unbalance protections. In the paper, the ratio of the unbalance current to the filter current and the over voltage are calculated during the evolution of the inner fault both in a single capacitor branch and in multiple capacitor branches. Based on the study, effective criterions and setting calculation methods are proposed for the HV capacitor unbalance protection.