Power differential protection as primary protection of transmission lines and busbars

Active power differential protection has recently been proposed as a novel technique to increase the protection reliability of transmission lines and busbars. In comparison with current differential protection, it is more reliable, faster, needs less input parameters and communication devices; those make it suitable to be used as a protection scheme of the wide area backup protection. On the other hand, active power differential protection cannot recognise the faulted phase of the protected object and therefore cannot operate for single pole tripping. In this paper, a new technique has been proposed to resolve the single pole tripping limitation of the active power differential protection. In this technique, when APDP relay produces trip command, an external logic compares per phase differences of the active power flowing at the line ends. For faulted phase, the difference is more than the others. The proposed technique has been evaluated using a MATLAB simulator configured to model effects of different faults on a typical 400 kV transmission line. The method has also been tested on simulated Northern Ireland Electricity (NIE's) 275 kV network to show the effectiveness of the proposed technique for a real system data. Results indicate that the new logic is reliable to be used as single pole tripping detector for APDP algorithm.