Fast voltage stability assessment and reinforcement in an interconnected power system

It is believed that voltage stability analysis will be more difficult due to the full utilization of transmission systems and the growth of inter-utility power transfer. An online voltage stability analyzing system which can be incorporated into the EMS to deal with the threats of suddenly arising voltage collapses is presented. Operating margin prediction, voltage stability assessment and reinforcement are three major functions. Two predicting methods are proposed to calculate the operating margin according to current operating condition and the anticipative system state. A fast risk indicator based on the saddle-node bifurcation theory is designed to predict the proximity of a system to voltage collapse. A novel CPF method which can trace the power flow solution path through the nose point without notorious numerical difficulties is presented. Speed is the advantage of former method, while accuracy is the important feature of latter one. Voltage stability assessment is required to predict steady-state conditions of a system following a large number of anticipated transmission branch or generator outages. An efficient and simple method based on voltage sensitivity changing rates is proposed for quickly identify the weak buses in a large-scale system. An effective contingency selection function relying on search algorithms built into power flow solutions is designed to filter out most of harmless contingencies for system operators who are working with rapidly changing load/generation patterns and a wide variety of operating conditions. A contingency evaluation function having the ability to deal with real-time numerous contingencies in a very short period of time is utilized to find high-severity contingencies. Var compensation and load shedding are two remedial measures of reinforcement function. Suitable var compensation scheme has three contributions: extending operating margin to avoid voltage collapses, fully utilizing the transmission infrastructure to earn economic benefits, and reducing the number of must-run units to eliminate monopoly profits. A load shedding method is designed to provide protection from fatal voltage collapses occurring outside of prior planning and operating studies. Two practical large-scale power systems and their interconnections are used to study voltage stability throughout this dissertation.