IMPROVEMENTS IN OR RELATING TO BIPOLE POWER TRANSMISSION SCHEMES

In the field of high voltage direct current (HVDC) power transmission schemes within HVDC power transmission networks, there is a need for an improved bipole power transmission scheme.A bipole power transmission scheme (10) comprises a first converter station (12) that is positioned in-use remote from a second converter station (14). First and second transmission conduits (20, 22) and a return conduit (24) interconnect, in use, the first converter station (12) with the second converter station (14) and thereby permit the first converter station (12) to transmit power to the second converter station (14). The first converter station (12) includes a first power converter (30) that has a first DC terminal (32) which is connected with the first transmission conduit (20), a second DC terminal (34) that is connected with the return conduit (24), and at least one AC terminal (36A, 36B, 36C) which is electrically connected with a first variable power source (38). The first power converter (30) further has a first converter controller (44) which is programmed to control the transfer of a first power infeed (46) from the first power source (38) into the first transmission conduit (20) in the form of a first power feed (76). In addition, the first converter station (12) also includes a second power converter (48) that has a first DC terminal (32) which is connected with the second transmission conduit (22), a second DC terminal (34) that is connected with the return conduit (24), and at least one AC terminal (36A, 36B, 36C) which is electrically connected with a second variable power source (50). The second power converter (48) further has a second converter controller (54) which is programmed to control the transfer of a second power infeed (56) from the second power source (50) into the second transmission conduit (22) in the form of a second power feed (86).The first power converter (30) and associated first power source (38) operate independently of the second power converter (48) and associated second power source (50) during operation of the bipole power transmission scheme (10) under normal conditions whereby the first power infeed (46) into the first transmission conduit (20) and the second power infeed (56) into the second transmission conduit (22) are independent of one another.During operation of the bipole power transmission scheme (10) under abnormal conditions, when the return conduit (24) is faulty and unable to provide a return current path, each converter controller (44, 54) is programmed to monitor the first power feed (76) in the first transmission conduit (20) and the second power feed (86) in the second transmission conduit (22) and, if the first power feed (76) in the first transmission conduit (20) and the second power feed (86) in the second transmission conduit (22) differ from one another, at least one converter controller (44, 54) modifies the power infeed (46, 56) from its corresponding power source (38, 50) to reduce the difference between the first power feed (76) and the second power feed (86).