Modal resonance in power system-A case study

Modal resonance occurring in the power system is a rare phenomenon, which has come into existence due to increasing complexity of the system. The power system is nonlinear in nature. Eigenvalue analysis is done for understanding the behavior of the system. Modal resonance is observed in power system when two eigenvalues of frequencies move very near to each other and collide. This results in either weak or strong resonance. In resonance condition, one of the modes exhibit a negative damping while the other exhibit positive damping. The negatively damped mode may result in system instability. This paper presents a practical case of modal resonance observed in Indian Power system. This phenomenon was analyzed with the help of synchronized measurements from the PMUs installed in the grid. The synchrophasor data was analyzed using Matrix Pencil Method for finding the eigenvalues corresponding to low frequency oscillation, and their damping during the observed frame.