Identification Method for Transformer Inrush and Fault Current Based on Waveform Partition and Reconstruction

Inrush current is an important factor affecting the correct operation rate of differential protection, which often occurs in power transformers. What’s more, the saturation of the current transformer (CT) caused by a large fault current will also affect the differential protection. In order to improve the reliability of transformer differential protection, this paper proposes an inrush current and fault current identification method based on waveform partition and reconstruction. Firstly, the waveform characteristics of inrush current and fault current with CT saturation are analyzed, and the key idea of this paper is the partition and reconstruction of differential current. Based on this idea, the differential current is divided into the linear region and the saturation region and reconstructed by using wavelet coefficient energy and second derivative energy as a joint criterion. Then the absolute value ratio of the amplitude is constructed according to the waveform trend, and the ratio is applied to determine whether the transformer is fault. Finally, through a large number of simulation tests, waveform analysis in various scenarios, and comparison with the traditional method, the effectiveness and superiority of the proposed method are proved.