IMPROVEMENTS IN OR RELATING TO BIPOLE POWER TRANSMISSION SCHEMES

In the field of high voltage direct current (HVDC) power transmission schemes, there is a need for improved detection of ground faults. [0002] A bipole power transmission scheme (12; 112) typically includes a first converter station (14) that is positioned remote from a second converter station (16), along with first and second transmission conduits (18, 20) which interconnect the first and second converter stations (14, 16) to permit the transmission of power between the first and second converter stations (14, 16). The first converter station (14) usually has first and second power converters (22, 24), with the first power converter (22) including a first DC terminal (26) that is connected with the first transmission conduit (18), at least one AC terminal (28) which is connected with a first AC network (30), and a second DC terminal (32) that is interconnected with a third DC terminal (34) of the second power converter (24) by a first interconnection (36) which defines a first neutral area (38). The second power converter (24) usually additionally includes a fourth DC terminal (40) that is connected with the second transmission conduit (20) and at least one AC terminal (42) which is connected with a second AC network (44). The first converter station (14) may additionally include a first grounding circuit (70) that is connected in use between the first neutral area (38) and ground (72) and is switchable into and out of operation, as well as at least one of a first current sensor (78), that is configured in use to measure the flow of current between the first neutral area (38) and ground (72), and a first voltage measurer (80), which is configured in use to measure the voltage difference between the first neutral area (38) and ground (72). Usually the second converter station (16) has third and fourth power converters (46, 48), with the third power converter (46) including a fifth DC terminal (50) that is connected with the first transmission conduit (18), at least one AC terminal (52) which is connected with a third AC network (54), and a sixth DC terminal (56) that is interconnected with a seventh DC terminal (58) of the fourth power converter (48) by a second interconnection (60) which defines a second neutral area (62). The fourth power converter (48) typically additionally includes an eighth DC terminal (64) that is connected with the second transmission conduit (20) and at least one AC terminal (66) which is connected with a fourth AC network (68). The second converter station (16) may additionally include a second grounding circuit (84) that is connected in use between the second neutral area (62) and ground (72), and is switchable into and out of operation, as well as at least one of a second current sensor (90), that is configured in use to measure the flow of current between the second neutral area (62) and ground (72), and a second voltage measurer (92), which is configured in use to measure the voltage difference between the second neutral area (62) and ground (72). [0003] The fault detector (10; 100; 110; 130) comprises a fault detector controller (96; 104; 122; 132) which is arranged in use in operative communication with the first and second grounding circuits (70, 84) and at least the first and second current sensors (78, 90) or the first and second voltage measurers (80, 92), and is programmed to detect a ground fault (150) in one or other of the first and second neutral areas (38, 62) by: configuring the first grounding circuit (70) to be in operation and the second grounding circuit (84) to be out of operation; checking for at least one of a first erroneous current flow in the first neutral area (38) using the first current sensor (78) and a first erroneous voltage in the second neutral area (62) using the second voltage measurer (92); recognising a ground fault (150) in the second neutral area (62) if a first erroneous current flow is identified or if a first erroneous voltage is identified; configuring the first grounding circuit (70) to be out of operation and the second grounding circuit (84) to be in operation; checking for at least one of a second erroneous current flow in the second neutral area (62) using the second current sensor (90) and a second erroneous voltage in the first neutral area (38) using the first voltage measurer (80); and recognising a ground fault (150) in the first neutral area (38) if a second erroneous current flow is identified or if a second erroneous voltage is identified.