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UBC Theses and Dissertations

A comprehensive simulation study of the voltage stability of a large power system Zhang, Wenjie


The voltage stability problem has become a growing concern in power system planning and operation. Many large interconnected power systems have experienced voltage insta- bilities which involve fast transients and/or slow dynamics. Although load flow related static approaches have been well developed to characterize the system maximum loading limit as the voltage collapse point, the mechanism of how system operation approaches its voltage collapse point and how this collapse point is affected by system dynamics are still obscure. This thesis provides the answers to these two basic questions through the investigation of effects of loads and reactive power controls on system voltage stability by detailed time domain system simulations. The importance of system dynamics in the determination of the voltage stability limit is emphasized. Firstly, a multimachine power system with steam and hydro electric generating units, various types of loads, and system reactive power—related control devices is appropriately modeled. Secondly, a comprehensive power system simulation program is developed based on the implicit trapezoidal rule and an integration step size control algorithm. A new variable elimination method for load flow, and a new forward—elimination and backward—substitution procedure for solving the system Jacobian matrix equations are devised. Different system disturbances are simulated, and the exact timing of system changes is implemented. Finally, a 21 bus sample power system is chosen for the voltage stability study. In the case studies, the effects of loads, control devices, and system disturbances on system voltage stability are thoroughly examined. The voltage instability of a power system is a very complicated phenomenon, which, depending on the location, the type, and the severity of a system disturbance, may involve a fast transient voltage instability, or a slow voltage deterioration followed by a sharp collapse. It is closely associated with system reactive power—related controls, and is strongly affected by the load characteristics. The beneficial and detrimental effects of loads and reactive power controls on voltage stability should be carefully analyzed so that the information can be used in voltage stability control designs.

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