Evaluation of stability and electric power quality in power system by using phasor measurements

The authors have developed a high-speed and high precision PMU (phasor measurement unit) by using a DSP (digital signal processor) and the GPS (Global Positioning System). The developed PMU enables to calculate the voltage and current phasors and the other state variables in power network systems from the measured instantaneous voltage and current in real-time. These phasor measurements provide vital information for stability analysis, and enable to evaluate power quality. In this paper, the authors propose a step-out prediction method in the power system using the phasor measurements. In this method, the power system is divided to the coherent groups of generators and each group is aggregated to one equivalent generator model. The aggregated model reflects the state and the structure of the actual power system at the present time. Then the state variables of each aggregated generator is estimated, at the same time the future phase angle is predicted by solving swing equations. In particular, the procedure and the evaluation of the effectiveness are confirmed in detail by some experiments using the real-time simulator (PSA).