Current differential protection is provided for a multi-terminal power apparatus, such as a power transmission line. Currents measured at each of the multiple terminals are used to calculate a differential current and a restraining current, which are then converted into a first equivalent current and a second equivalent current of an equivalent two-terminal power apparatus. In the equivalent two-terminal power apparatus, a differential current derived from the first and second equivalent currents is substantially equal to the differential current of the original multi-terminal power apparatus. Similarly, a restraining current derived from the first and second equivalent currents is substantially equal to the restraining current of the original multi-terminal power apparatus. The first and second equivalent currents may be used in an alpha plane analysis to determine whether or not to trip the multi-terminal power apparatus.