A Study on the Phenomenon of Voltage Instability in Power Systems

This thesis presents an investigation of voltage stability assessment in radial distribution systems based on static methods. A new voltage stability index is derived and introduced for evaluating the severity of the loading situation of the given system, thereby predicting for voltage instability at definite load value. Comparison between the results of the new index and those of the previous indices shows that the new index yielded reliable results in predicting the phenomenon of voltage instability. A new method for determining the voltage stability limit using the P-Q plane is presented. In that, method the boundary of the voltage stability region is first determined and then it is presented in the P-Q plane. A method for identifying the weak buses in radial distribution systems is presented. This method is based on a previously introduced voltage stability index, which can be evaluated at each bus of the system. Artificial Neural Network (ANN) based modeling techniques for predicting voltage stability of radial distribution systems based on two different voltage stability indices are also presented.