Voltage stability problem in a distribution system with distributed generator

Abstract

With difficulties in building new transmission lines and power plants, due to environmental and political issues, while electricity demand is continuously increasing, it is expected that, in the near future, more distributed generations will penetrate into power systems, especially into the distribution system. As several competitive advantages of an induction generator compared to a synchronous generator such as durability, low investment cost and etc., it is possible that many of very small power producers may connect this type of generators into the distribution system. However, as we know, rather than generate reactive power, the induction generator consumes it. Thus, impact of the induction generator on voltage stability should be carefully investigated. We focus on this aspect in this thesis. Both static and dynamic analyses were performed in this thesis. In static analysis, the degree of voltage instability based on PQVSI index is used as the main tool to assess how close the present operating condition to the voltage instability point. In addition to the static analysis, the dynamic voltage stability was conducted as well. The dynamic voltage characteristics were observed, which is eventually used to verify the results obtained from the static analysis. It provides clearer and more accurate figure of the actual dynamics of voltage instability process following a disturbance in the system, which in this case is a load change. The studies indicating an unhealthy impact of induction generators on the system’s voltage stability are shown in this thesis, especially when the system is intended to serve large inductive loads. These phenomena lead to both unstable of the induction generator itself, and unstable of the entire distribution system through voltage instability. As a consequence, special treatment should be implemented in the case of utilizing induction generators in the distribution system. An example treatment in this study, which is disclosing the advantage of installing capacitor at the induction generator terminal in enhancing the utilization of the induction generator, had been presented.