Long-Term Voltage Instability Detections of Multiple Fixed-Speed Induction Generators in Distribution Networks Using Synchrophasors

As the penetration of renewable energy sources is increasing, the long-term voltage stability (LTVS) of fixed-speed induction generators (FSIGs) has raised a major concern for distribution power networks since they will always consume reactive power. When either the voltage profile of the FSIG severely declines due to the load consumption increasing in the nearby area, or the mechanical power of the wind turbine increases owing to the wind speed increasing, the loss of the stable equilibrium point will result in this class of long-term voltage instability problems. Although this problem is a local phenomenon, it may spread to the rest of the system and cause the cascaded blackout. Meanwhile, with massive deployment of synchrophasor technology, it is possible to improve system awareness and enable early warning to detect this class of LTVS problems in real-time. In this paper, a measurement-based algorithm for synchrophasor long-term voltage stability indicator (SLVSI) will be proposed. First, qualitative analysis of this class of LTVS problems is conducted by corresponding bifurcation diagrams and hysteretic curves. Secondly, a measurement-based FSIG equivalent model is proposed by utilizing real-time phasor measurements from synchrophasors. The above concept can be extended to distribution power networks with multiple FSIGs. The entire distribution power grid will be considered as a modified coupled single-port network. By exploring the concept of reactive power response factor, the corresponding Thevenin equivalent parameter of each individual FSIG branch is adjusted based on real-time phasor measurements. Thus, a SLVSI for each individual FSIG can be defined by modifying the conventional L-index. Simulation experiments on two IEEE test systems are performed to validate the accuracy of the proposed SLVSI.