Study On The Detection Method Of Inrush Current In Transformer

Power transformers are the important electric equipments of power system, and their security and stability are extremely important to entire power system operation. In the process of transformers no-load closing or voltage recovery after the remove of external fault, inrush current will be produced whose amplitude may reach several times even nearly ten times of the rated current. As the inrush current only flows through the power side of the transformer, it will flow into the differential circuit of the transformer longitudinal differential protection. If the inrush current cannot be identified, longitudinal differential protection may wrongly operate. Thus, in order to ensure the correct operation of transformer differential protection, inrush current and internal fault differential current must be identified accurately and reliably.In this paper, the transformer inrush current identification literature home and abroad are covered. The methods to identify inrush current are classified according to principles, and their advantages and disadvantages are analyzed. The transformer inrush current generation mechanism, the maximum peak, minimum break angle, and the minimum second harmonic are study deeply. The factors impacting transformer inrush current are analyzed. On the basis of analyzing the transformer inrush current and the characteristics of the fault current waveform, with comparing the wave and half-wave difference Fourier algorithms when doing the inrush current calculation, a recognition method of transformer inrush current based on combination of fluctuation error and peak-to-peak space method is proposed in this paper.The proposed magnetizing inrush current detection method is simple in calculating, clear in principles and impregnable of initial time. It can identify the one-way inrush current and the symmetry inrush current. Additionally, this method reflects the essential characters of inrush current, and is easy to set. Many simulation results indicate that the proposed method has a good effect in detecting transformer inrush current.