IMPROVEMENTS IN OR RELATING TO DIRECT CURRENT DISTANCE PROTECTION SCHEMES

摘要

In the field of DC electrical power networks there is provided a DC distance protection scheme (10; 60; 80; 90; 100; 110) for protecting a DC power transmission medium (20) within a said DC electrical power network (12). The DC distance protection scheme (10; 60; 80; 90; 100; 110) comprises a protection device (16; 64; 84; 94; 104; 114) that is coupled in use to a DC power transmission medium (20). The protection device (16; 64; 84; 94; 104; 114) is operable to protect the DC power transmission medium (20) from an electrical fault. The DC distance protection scheme (10; 60; 80; 90; 100; 110) also includes a measurement apparatus to selectively measure the current (i m ) and voltage (u m ) of the DC power transmission medium (20). In addition the DC distance protection scheme (10; 60; 80; 90; 100; 110) also includes a controller (22, 62; 82, 92, 102, 112) that is programmed to: (i) calculate an operating voltage (u op ) of the DC power transmission medium (20) using the measured current (i m ) and voltage (u m ); (ii) perform a transient comparison between the calculated operating voltage (u op ) and the measured voltage (u m ); and (iii) operate the protection device (16; 64; 84; 94; 104; 114) to protect the DC power transmission medium (20) if the transient comparison meets a predefined criterion.