Cost-effective solutions for handling dc faults in VSC HVDC transmission

Utilization of voltage-source converters (VSC) in high-voltage direct current (HVDC) transmission systems are increased in recent years. This paper proposes cost-effective solutions for handling dc-side faults in VSC HVDC bipolar transmission. The basic idea of this paper is to replace the existing mechanical neutral bus switch (NBS), which is normally composed of resonance circuit and mechanical breaker, with semiconductor-based dc breakers. Consequently, converter blocked-time can be reduced significantly and ac grid can be supported with reactive power within a short time. The proposed method will improve the stability of the connected ac grid.