The Research On A Ranking Method Of Contingency In Transient Stability Analysis

Online stability analysis and control is very important for security and economical operation of the power system. With the development of electric electricity market, the implementation of electricity transferring from the west to the east and national electric power network interconnection, it is realized that online stability analysis is one of the most important means for the system security operation. This paper studies the ranking of the potential contingencies. The difficult point of the transient stability analysis is that the solution needs fast computation speed and accuracy. For the purpose, the advantage of both explicit method and implicit method is combined, and a good numerical implicit integration with the performance of high precision and high computation speed is proposed in this paper. The proposed method improves the computation speed of current implicit numerical integration method used by the power industry significantly. Both of them have the same accuracy. Practical large scale system simulation shows that the method has good accuracy and computation speed and can be used for online power system stability analysis. Meanwhile, under two-group instability modes, it is discovered that the curves between electric power of generator unit and rotator's angle in relative to center of inertia is a sine curve. By using single machine equal area criterion (SGEAC) and combining with time domain simulation method, the disturbed system is simulated for a very short time period. According to the simulation result, the curve between electric power of generator unit and rotator's angle in relative to center of inertia is fitted. Maximum deceleration area or maximum acceleration area of each unit is obtained according to the fitted curves and then the stability margin and instability margin for the system are obtained. According to the margin, the potential contingency set is ranked. The advantage of the method in this paper is that it is not necessary to simulate the disturbed system to the instant when the system loses its stability in order to determine whether the system is stable or not. For stable system, the stability margin based on single machine energy can be obtained. Compared with other methods, it is not necessary to determine the correct two group mode. Practical system analysis shows that the method is very fanst, very reliable and very efficient, and it should have wide engineering applications for on-line stability monitoring.