基于波形互相关系数的变压器励磁涌流识别方法

励磁涌流是导致变压器差动保护误动的主要因素。提出一种利用波形互相关系数特征的励磁涌流识别方法。利用空载合闸或内部故障后的短数据窗构造一标准正弦参考波,对采样波形与构造的标准正弦波两信号的相关性进行分析,计算归一化互相关系数进行内部故障和涌流识别。内部故障时波形互相关系数为接近1的稳定值,而励磁涌流时互相关系数偏离1且其值波动显著。最后PSCAD仿真计算分析结果表明:该方法能在一个周波内准确识别出励磁涌流与内部故障,为提高变压器差动保护性能和优化变压器保护配置提供了有益的理论依据。

A novel algorithm of identifying inrush current based on waveform cross-correlation coefficient

The inrush current is the main factor that leads to misoperation for transformer differential current protection. This paper proposes a novel algorithm based on waveform cross correlation principle for distinguishing between magnetizing inrush current and internal fault currents. Either in the case of no-load switching or internal faults, a short sampling data-window is used to produce a normal sine wave as reference, and then calculate the normalized cross-correlation coefficient between the practical sampled waveform and the reference. In the condition of internal faults, the normalized cross-correlation coefficient is close to 1. But in the situation of inrush current, it is deviated from 1 and waves notably. Therefore, the calculated normalized cross-correlation coefficient is used to detect internal faults and inrush current. PACAD simulation results indicate that the proposed algorithm can identify inrush current and internal faults correctly and quickly, and it is helpful to supply theoretical basis for improving the performance of differential protection and optimizing protection scheme in transformers.