Concepts for Secured Protection of VSC HVDC Overhead Lines Equipped with Auto Reclosing of DC Circuit Breakers

This paper has analyzed the transients of DC voltage and DC currents during auto reclosing of HVDC circuit breakers to an overhead DC line fault of a VSC HVDC grid. When the line is energized by reclosing the HVDC breaker the voltage and current transients behave differently from the transient following the initial DC fault. Furthermore, the transients observed during auto reclosing differs between permanent and temporary DC faults. A robust DC line protection system that accounts for the transients following auto reclosing to avoid unwanted trips on the DC line has been designed. Numerical tests using PSCAD shows improvement in security of protecting overhead lines in VSC HVDC grids.