Development of Stability Evaluation Method by On-line Measurement of Eigen Frequencies of Power Systems

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On-line measurement method of eigen frequencies of power systems by SMES has been already proposed. When SMES gives the forced power perturbation to the power system, its transient response is measured and analyzed. The purpose of this study is to develop the on-line evaluation and observation method of power systems stability based on the on-line measurement of eigen frequencies of power systems by SMES.The eigen frequencies of power systems are measured experimentally, using the one-machine infinite-bus artificial power system and 50kJ SMES. When the number of core-less coils between the generator and the infinite bus is changed, the stability margin of the power system is changed. It is confirmed experimentally that the eigen frequency of the main mode becomes lower as the system moves to unstability.From the experimental and numerical results, the on-line evaluation and observation method of power systems stability is proposed. The method is as follows: the eigen frequencies of power systems are measured on-line every several minutes. When the eigen frequency moves low and beyond the threshold, it is measured continuously. When it moves lower, the stability improvement strategy is executed. Then the operator should confirm the eigen frequencies move high and the system recovers stability. The proposed on-line evaluation and observation method of power systems stability by measurement of eigen frequencies is studied basically in the experimental studies. Moreover, by the numerical studies, the application ability of the proposed on-line evaluation and observation method to the three-machine longitudinal system. By this study, it is made clear that the proposed method can be applied to the multi-machine longitudinal system which structure is simple.It is necessary to study and investigate the ability of the proposed method to the multi-machine system, which has the loop and so on.