Abstract: The present invention relates to a high voltage direct current (HVDC) transmission system (200) comprising a first bipole (210) comprising a first transmit station (220) and a first receive station (230) and a second bipole (250), connected to the first bipole (210), the second bipole (250) comprising a second transmit station (260) and a second receive station (270). The HVDC transmission system includes: a first HVDC transmission line (280) for coupling a negative node (2206) of the first transmit station (220) to a negative node (2306) of the first receive station (230); a second HVDC transmission line (290) for coupling a positive node (2208) of the first transmit station (220) to a positive node (2308) of the first receive station (230); a dedicated metallic return (DMR) (285, 295) for coupling a neutral node (2210a) of the first transmit station (220) to a neutral node (2310) of the first receive station (230).