| For a long time, the stability theory and analysis method of power system emphasize particularly on power-angle stability. On the base of mechanism of power-angle stability, a suit of mature analysis method and control measure was developed. But recently years, there were a lot of voltage collapse accidents due to voltage instability, Power system voltage instability or voltage collapse is an important factor in power System instability. Because voltage collapse accident can cause great economic loss and bad influence to the society, it becomes an emergent problem to be solved for the security of power system.The level of voltage is closely with reactive power. Being a practical dynamic reactive compensator, static var compensator (SVC) have been used widespread, but there are just a few studies about voltage stability with SVC , So in this paper, the voltage stability of power system with SVC will be studied deeply from static and dynamic state.Using of Voltage stability index to research static voltage stability. Ranking sensitivity indexes of reactive network loss can judge the weak nodes quickly in the system. Based on it, the paper gives second-order transformation, which overcomes nonlinear properties of original indexes and determines load margin better. And SVC is installed in weak node. The paper analyses voltage stability indexes of Pre and Post installation by simulating WSCC nine system, and the result proves that the system that includes SVC can reduce sensitivity and improve voltage stability. And it can predict load margin exactly by improving second order index.The paper analyzed dynamic voltage stability of WSCC nine-system with PSAT. The paper simulated three typical large disturbances-load disturbance,line break and three-phase short circuit, compared with voltage stability of system with SVC and without. Last, modeled induction motor as load model, this essay researched the influence to voltage stability when the insufficiency capability of SVC.
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