Using Direct Method To Analysis Power System Transient Stability

Stability wreck is the most serious accident in the network. To prevent stability wreck, direct method as a quick, precision stability analysis method, many countries have made a great deal of research on it. There are two trends in direct stability analysis: one is to improve on existent model, seeking more nicety, faster and more practicability method. The other is to find out new theory and method to analysis online stability.The specialty of direct method is that it analysis the stability from the point of energetic rather than by means of calculate the system movement track. The strongpoint of direct method is its quick speed and it can also quantify the degree of stability .So we can use it as an on-line tool to analysis dynamic security and an out-line security analysis tool for large quantity scanning.This thesis includes such contents:At first, the thesis systematically reviews and summarizes the development state of the direct method inside and outside the country. Combines with single machine-infinite system, this thesis presents the process of transient-stable analysis by using direct method: the definition of transient energetic function and its calculation, how to fixes the critical energy, and it also gives the standardized margin degree of stability. The thesis compares the direct method with equal-area criterion and explicates their uniformity.This thesis introduces the math model of direct transient-stable analysis method under multi-machine system synchronism coordinates and gives the conception of RUEP; then derivates COI coordinates and gives UEP math model under COI coordinates and points out the differences between the two methods; then explains COI coordinates is more reasonable than synchronism coordinates, using double-machine kinetic energy adjustment can amend accuracy. On this basis discusses the calculation procedure of direct transient-stable analysis method, gives examples and discusses the reason of inaccuracy.The thesis establishes the double-machines model and the three-machines model. In consideration toincrease the calculation speed, the thesis adopts detail model near the fault site and employs simplified model on other sites. By using this method we can not only satisfy the need for engineering accuracy but also can limit the calculation in the fault subset in favor of increase the calculation speed and we can quickly calculate the sustained fault pathway and make stability judgments. Network equation usesdecomposition-aggregation method. After calculate the critical excision angular, this thesis uses sectionalized calculation method to work out the critical excision time. A software using direct method, the double-machines model is programmed on the basis of the building model. The results gained by using the recommended power system (22 points) are satisfied.