基于能耗的变压器励磁涌流与故障电流识别判据

Discrimination Between Magnetizing Inrush and Fault Currents Based on Energy Dissipation Criterion

变压器差动保护利用二次谐波制动原理或间断角制动原理来区分故障电流和励磁涌流,由于超高压系统故障电流中也含有较大的二次谐波,易导致变压器故障时保护动作延时,间断角制动原理则会因互感器饱和引起的涌流间断角消失而使保护误动.提出了一种基于能耗区别的方法识别励磁涌流和故障电流,克服了上述问题.同时采用高斯-牛顿最小二乘法拟合励磁涌流,克服了傅里叶算法受频率变化影响较大的缺陷.仿真结果验证了所提方法的可行性.

In the transformer differential protection,the second harmonic restraint and the dead angle restraint principles are the two major criterions to discriminate inrush current from fault currents.But in the super-high voltage system,there is also plenty of second harmonic in the fault current.The second harmonic here is of great probability to result in the tripping delay.Meanwhile,the dead angle restraint principle would result in misjudge due to the disappearance of dead angle during the CT saturation.To overcome these shortages,this paper presents a new method to discern inrush current from fault currents using energy dissipation criterion.The least square curve-fitting is adopted to fit the inrush current so as to overcome the shortage of the Fourier algorithm which is sensitive to frequency change.The results of dynamic simulation verify the feasibility of the proposed method.