阻抗不均导致振荡中心迁移的规律

基于计及阻抗不均的等值两机系统模型,采用向量图和数值计算相结合方法研究了线路阻抗不均导致振荡中心偏移的规律。定义两机系统总阻抗模值的中点为系统中心。在系统功角由0?360?摆周期中,系统阻抗角不等可导致振荡中心动态迁移:当系统中心落在联络线上时,振荡中心仅在联络线内部动态迁移。当系统中心落在联络线任侧系统等值阻抗上时,存在两种迁移规律,是仅在联络上动态迁移,二是振荡中心在联络线和系统中心所在的联络线侧等值阻抗上动态迁移。系统失步中心位置(振荡周期内电压过零点)不受阻抗不均的影响,不影响失步中心位置的定位,但失步中心并非只在系统功角摆至180?时出现。

New method to determine optimum impedance of fault current limiters for symmetrical and/or asymmetrical faults in power systems

To select the type and value of the impedance of fault current limiters（FCLs） for power network designers, we introduce a new method to calculate the optimum value of FCL impedance depending on its position in the network. Due to the complexity of its impedance, the costs of both real and imaginary parts of FCL impedance are considered. The optimization of FCL impedance is based on a goal function that maximizes the reduction of the fault current while minimizing the costs. While the position of FCL in the network has an effect on the calculation of the optimum impedance value, the method for selecting FCL location is not the focus of this study. The proposed method for optimizing FCL impedance can be used for every network that has symmetrical and/or asymmetrical faults. We use a 14-bus IEEE network as an example to explain the process. The optimum FCL impedance used in this network is calculated by considering the vast range of costs for both real and imaginary parts of FCL impedance.