A high-voltage DC (HVDC) power system comprising: a plurality of sending-end modules coupled in electrical series and divided into at least two groups (111, 113) that each operate independently with respect to an electrical ground; and a plurality of receiving-end power converter modules electrically coupled to said plurality of SE modules, the plurality of RE power converter modules including a fast ground-fault detection and control device; the plurality of RE power converter modules including a receiving-end front-end DC-DC converter controller, and an output current damping control, the system further comprising a bipolar configuration having an earth ground and two opposite polarity transmission cables (504, 506) supplying the RE modules from the SE modules, the output current being the current between the SE modules and the RE modules, characterised in that the ground fault detection and control device comprises: a first current sensor configured to measure load current entering a load distribution cable; a second current sensor configured to measure load current entering a RE power converter module downstream from the load distribution cable; a ground fault detector configured to compare a residual common mode current measured by the first and second current sensors to a threshold and generate a ground fault command; and a load isolation device (516, 519) configured to isolate a ground fault from the HVDC power system based on the generated ground fault command. a plurality of sending-end modules coupled in electrical series and divided into at least two groups (111, 113) that each operate independently with respect to an electrical ground; and a plurality of receiving-end power converter modules electrically coupled to said plurality of SE modules, the plurality of RE power converter modules including a fast ground-fault detection and control device; the plurality of RE power converter modules including a receiving-end front-end DC-DC converter controller, and an output current damping control, the system further comprising a bipolar configuration having an earth ground and two opposite polarity transmission cables (504, 506) supplying the RE modules from the SE modules, the output current being the current between the SE modules and the RE modules, characterised in that the ground fault detection and control device comprises: a first current sensor configured to measure load current entering a load distribution cable; a second current sensor configured to measure load current entering a RE power converter module downstream from the load distribution cable; a ground fault detector configured to compare a residual common mode current measured by the first and second current sensors to a threshold and generate a ground fault command; and a load isolation device (516, 519) configured to isolate a ground fault from the HVDC power system based on the generated ground fault command. a first current sensor configured to measure load current entering a load distribution cable; a second current sensor configured to measure load current entering a RE power converter module downstream from the load distribution cable; a ground fault detector configured to compare a residual common mode current measured by the first and second current sensors to a threshold and generate a ground fault command; and a load isolation device (516, 519) configured to isolate a ground fault from the HVDC power system based on the generated ground fault command.