Improving Mho and Quadrilateral Relays Performance during Power Swings

Ibrahim, D. K., A. F. Zobaa, E. A. El-Zahab, and G. M. Abo-Hamad, "Improving Mho and Quadrilateral Relays Performance during Power Swings", International Review of Electrical Engineering, vol. 5, issue 6: Praise Worthy Prize, FEDERICO II University 21 Claudio Naples I 80125 Italy, 2010.


Power swings, both stable and unstable, may precipitate wide spread outages to power systems with the result that cascade tripping of the power system elements occur. This paper deals with improving Mho and Quadrilateral relays performance under power swing conditions by discriminating between faults and power swings phenomenon. Distance relay may misinterpreted power swing as three-phase fault, but wavelet transform is able to discriminate clearly between power swings and faults. So, a logic block for fault detection based on the wavelet transform combined with the output of the conventional distance relay is proposed. Only voltage signals are used in wavelet relay to distinguish between fault and power swings conditions. The described scheme has been tested on a double line simulated power system using MatLab program.