Electrical System Transient Stability Analyse By Direct Method

With the development of economy and the advancement of the technology, the tradition power system is experiencing a process along the way from regional power supply to the large-scale connected power system. This trend brings a great economic benefit, while at the same time, a serious challenge to the stability of the power systems, especially the transient stability. The direct method is one of the most important methods in the transient stability analysis. To analyze and determine the transient stability of the post-default system by the direct method is an important task for the research on power systems' stability. Many countries have made a great deal of research on it. Great process has been made over thelast decades.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 online tool to analysis dynamic security.The main research work has been developed as follows: 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 requirement, and it also gives the standardized margin degree of stability. The thesis compares the direct method with equal-area criterion and explicates their uniformity. Reason out the function of power network's classical math model and the model of multi- electrical machine system.This thesis introduces the direct method such as Liapunov, UEP, PEBS, EEAC, and so on, combines with one machine to infinite bus system to introduce the energy of transient, the energy of critical, the margin degree of stability. Compare the advantage and disadvantage of these direct mothod, and the area each applied. Be compare with them, EEAC method is good at the calculate of stability abundant CCT> analyse the characteristic of lost stability after two or more swings. Compare with the method of step by step, to validate the direct method's trustiness, speediness.The direct method is supplement of step by step method, they can't replace each other. Based on the analysis of direct method, the thesis combined these two methods, use their advantages, use the method of divide up the system to two parts by the max angel gap. The step by step method can abtain the exact result, and the EEAC method can give the criterion of end of iterative. Base on the theory, open out the application to analyze the transient stability of power system. The results gained by using the recommended power system(22 points) are satisfied.