Investigation Of Power System Voltage Stability Contingency Ranking

With the fast development of the electric industry, the scale of the power system becomes much larger, and the stability of the power system has become the focus of research. So it has become an important task of researchers and engineers to investigate the mechanism of the instability of system voltage, seek the factors affecting voltage stability, and estimate the severities of contingencies in the system.This thesis begins with the analysis methods and indices of voltage stability. The main contributions are:1. After comparing different indices, the second-order index based on loss sensitivity is chosen to estimate the severities of system contingencies. This index has the merits of better linearity and shorter calculating time. It can estimate the load margins in all kinds of situations appropriately.2. By simulating a simple power system, it is proved that there is a relationship between the var reserve and the voltage stability margin. The validity is verified by simulating a real power system. The relationship gives the dispatcher an approach to find out the voltage stability margin of the system and analyze the system stability.3. The program of system contingency ranking using the second-order index based on loss sensitivity is designed in Visual C++. This program also offers an interface with PSD-BPA. Calculate the second-order index based on loss sensitivity in different contingencies.4. The results of simulating real power systems show that a tightly connected power system can be hardly affected by the external systems. So the effects of the external systems can be whole or partly omitted when calculating voltage stability indices.5. The effects of different load models to power system voltage stability are studied by simulating the voltage responses after contingencies. Two kinds of voltage stability indices considering characteristics of loads are investigated. They can be used as the complements of the sensitivity index.