Transmission line impedance-differential protection with improved stabilization for external fault cases

In this paper, the enhanced impedance-differential protection algorithm dedicated for transmission lines is described. Measurements of current and voltage at both line ends allow to formulate a differential impedance which constitutes efficient criterion for transmission lines protection. The considered impedance-differential protection can be used as a main transmission line protection. It can be observed that this protection may face problem when external faults with CT saturation take place. Therefore this paper presents an improved scheme based on phase angle impedances calculated at both ends. The proposed algorithm provides better stabilization for cases of external fault with CT saturation. The developed protection solution has been thoroughly tested with the signals generated with use of ATP-EMTP program.