中文摘要：

等效瞬时电感算法是区分励磁涌流和故障电流的有效方法,但220 k V及以下电压等级的Y/△接线三相变压器多采用三相一体式结构,△侧环流难以获取,因而限制了该算法在此类变压器中的应用。提出一种计算环流的新方法。首先利用变压器等效电路的微分方程,推导出△侧环流和Y侧零序电流的比例关系。在磁通不饱和区域,Y侧对应相电流和环流相等,因而也和零序电流成比例。然后利用波形相关度理论,分别求取Y侧三相电流与零序电流的相关系数以区分磁通不饱和区域,证明至少可以获取一相长度足够的磁通不饱和区域。利用该段区域内的电流求出比例系数,进而可由Y侧零序电流求得△侧环流。最后通过MATLAB仿真验证了该方法求取△侧环流的准确性。该方法无需已知变压器参数,也无需控制合闸角,在一个工频周期内就能准确求取环流。

英文摘要：

The equivalent instantaneous inductance algorithm is an effective way to distinguish the excitation inrush from the fault current,which could not be easily applied to the 220 k V and below threephase transformers with Y / △ connection due to the hardly acquired circulating current of delta winding.A method for calculating the circulating current is proposed. The proportional relationship between the circulating current of delta winding and the zero-sequence current of Y winding is derived based on the differential equations of transformer. In the unsaturated flux zone,because the circulating current is equal to the corresponding phase current at Y side,it is proportional to the zero-sequence current as well. In order to distinguish the unsaturated flux zones,the waveform correlation theory is applied to calculate the correlative coefficient of phase current with zero-sequence current for each phase at Y side,which proves that the unsaturated flux zone of at least one phase is long enough for calculating the ratio of phase current over zero-sequence current to obtain the circulating current. The accuracy of the proposed method is verified with MATLAB simulation. With the transformer parameters unknown and the closing angle uncontrolled,it calculates the circulating current accurately within one power cycle.