Study On Mode Instability In Electric Power System With Close Modes

There exist many close modes in large power system.The close modes have great impacts on the dynamic characteristic of power system.This paper concentrates on the research of power system with close oscillation modes.The mechanism of modes instability, the method for determining the close oscillation modes, modes instability and its influential factors are analyzed in depth.A perturbation technique for complex modes is used to make modal analysis of the close modes shapes in a power system which confirms the mechanism of modes instability in power system.Based on the relevance of the dominant generators participating in oscillation mode and the closeness of oscillation frequency, a new way is prompted to determine close oscillation modes.The test systems are employed to verify the effectiveness of this determination method.In order to analyze the variations of right eigenvectors and left eigenvectors in close mode power system, generator parameters in the10-machine New England and the NPCC48-machine test systems are changed. It shows that the left eigenvectors and right eigenvectors of close modes change a lot after the perturbation of system parameters, which could easily change participant factors. The two test systems are also employed to study the modes instability and its characteristics under system multi-operating modes, the results of examples show that the occurrence of modes instability is closely related with the change of operation modes. The disturbances of loads which are next to generators participating in close modes will make systems modes unstable easily.