In the field of multi-terminal electrical power network protection, a protection apparatus comprises a measurement apparatus to measure the respective terminal current (IL, IR1, IR2, IR3, IR4, IR5) flowing at each terminal (L, R1, R2, R3, R4, R5) in a multi-terminal network that includes a plurality of electrically interconnected terminals (L, R1, R2, R3, R4, R5). The protection apparatus also includes a control unit that is programmed to process the measured terminal currents (IL, IR1, IR2, IR3, IR4, IR5) to obtain first and second summed values (IPOS(n), INEG(n)). The first summed value (IPOS(n)) is the sum at a given time (n) of the or each terminal current (IL, IR1, IR2, IR3, IR4, IR5) flowing in a first direction (Di) relative to a corresponding terminal (L, R1, R2, R3, R4, R5) and the second summed value (INEG(n)) is the sum at the same given time (n) of the or each terminal current (IL, IR1, IR2, IR3, IR4, IR5) flowing in a second direction (D2) opposite the first direction (D1) relative to the corresponding terminal (L, R1, R2, R3, R4, R5). The control unit is further programmed to compare the phase of the first summed value (IPOS(n)) with the phase of the second summed value (INEG(n)) to determine whether a fault in the multi-terminal network is internal or external to the multi-terminal network and thereafter to produce an internal fault output signal upon the determination of an internal fault.