A DC protection scheme (10, 110, 210, 310, 410, 510) for protecting a DC power transmission medium (16, 116, 216) within a DC electrical power network, the DC protection scheme (10, 110, 210, 310, 410, 510) comprising: a protection device (14, 114, 214) coupled in use to a DC power transmission medium (16, 116, 216), the protection device (14, 114, 214) being operable to protect the DC power transmission medium (16, 116, 216) from an electrical fault; a measurement apparatus to selectively measure at least one electrical property of the DC power transmission medium (16, 116, 216); and a controller (18, 118, 218), the DC protection scheme (10, 110, 210, 310, 410, 510) being characterised in that the controller (18, 118, 218) is programmed to: (i) determine the direction of the electrical fault by comparing the forward and backward travelling waves derived from the or each measured electrical property; (ii) determine whether the electrical fault is an internal or external fault by comparing a first with a second frequency component derived from the or each measured electrical property, wherein the frequency of the first frequency component is higher than the frequency of the second frequency component; and (iii) operate the protection device (14, 114, 214) to protect the DC power transmission medium (16, 116, 216) if the determination of the direction of the electrical fault and the determination of whether the electrical fault is an internal or external fault meet a predefined criterion. a protection device (14, 114, 214) coupled in use to a DC power transmission medium (16, 116, 216), the protection device (14, 114, 214) being operable to protect the DC power transmission medium (16, 116, 216) from an electrical fault; a measurement apparatus to selectively measure at least one electrical property of the DC power transmission medium (16, 116, 216); and a controller (18, 118, 218), the DC protection scheme (10, 110, 210, 310, 410, 510) being characterised in that the controller (18, 118, 218) is programmed to: (i) determine the direction of the electrical fault by comparing the forward and backward travelling waves derived from the or each measured electrical property; (ii) determine whether the electrical fault is an internal or external fault by comparing a first with a second frequency component derived from the or each measured electrical property, wherein the frequency of the first frequency component is higher than the frequency of the second frequency component; and (iii) operate the protection device (14, 114, 214) to protect the DC power transmission medium (16, 116, 216) if the determination of the direction of the electrical fault and the determination of whether the electrical fault is an internal or external fault meet a predefined criterion. (i) determine the direction of the electrical fault by comparing the forward and backward travelling waves derived from the or each measured electrical property; (ii) determine whether the electrical fault is an internal or external fault by comparing a first with a second frequency component derived from the or each measured electrical property, wherein the frequency of the first frequency component is higher than the frequency of the second frequency component; and (iii) operate the protection device (14, 114, 214) to protect the DC power transmission medium (16, 116, 216) if the determination of the direction of the electrical fault and the determination of whether the electrical fault is an internal or external fault meet a predefined criterion.