As one of the huge power transmission modes

high voltage direct current(HVDC)transmission system with parallel converters(HVDC_PC)requires that faults in one converter do not influence another non-fault converter to operate. Based on an analysis of the fault features in different fault positions and types of converter area in HVDC_PC

a clearing action requiring rectifier to retard is proposed to isolate the fault converter while maintaining the non-fault converter operation. As a backup of rectifier not to retard for some reason or other

it is suggested that the trip delay-time of direct current line under-voltage protection be set to about 50 ms. For a grounded fault on alternating current system in the inverter

it is possible for two parallel converters to share the fault current due to commutation failure. The current is less than that for multi-terminals HVDC with parallel type under the condition of similar direct current transmission system parameters. This work is supported by State Grid Corporation of China.