To address the issue that fault currents caused by grounding faults on the valve AC side of bipolar VSC-HVDC systems have no natural zero-crossing points

the characteristics of fault currents at both the faulty and healthy terminals after converter blocking at the faulty end are analyzed. Analytical expressions are derived

and a criterion and corresponding protection scheme for the healthy terminal to identify grounding faults on the opposite side are obtained. Since arc currents that reverse and pass through a zero crossing are beneficial for restoring the dielectric strength of the arc gap in AC circuit breakers

the impact of reducing DC voltage after a fault on the reverse zero-crossing behavior of valve AC-side fault currents is investigated. Based on this

a protection scheme is proposed in which

after the healthy terminal is taken out of operation

the non-grounded pole on the DC side of the faulty terminal is grounded through a resistor. The expressions for the current limiting resistor and the valve AC-side fault currents are derived. Finally

simulations are performed on the PSCAD/EMTDC platform. The results demonstrate that grounding the non-grounded pole through a resistor can not only enable reverse zero-crossing of valve-side fault current of the converter transformer

but also effectively prevent the occurrence of three-phase short circuits in the converter transformer.