A DC protection scheme for protecting a DC power transmission medium within a DC electrical power network. The scheme includes a protection device coupled to a DC power transmission medium, being operable to protect the power transmission medium from a fault; an apparatus to measure at least one electrical property of the power transmission medium; and a controller programmed to determine the direction of the electrical fault; determine whether the electrical fault is an internal or external fault; and operate the protection device to protect the DC power transmission medium if the determination of the direction of the electrical fault and/or the determination of whether the electrical fault is an internal or external fault meet a predefined criterion.