Research Of Identification Methods And Inhibit Strategy Of Transformer Excitation Inrush Current

With the rapid development of economy, industries put forward higher requirements on power system. Power transformer plays a switching hub function in the power system, its safety and stability are directly related to the stability of the whole power grid. Along with the deepening of relay protection technology, the correct action rate of transformer protection is improved, but in terms of line protection and bus protection, the correct action rate of transformer protection is still at a low level. The main reason is that, as the main protection of transformer, the differential protection has its congenital defects -- the protection scope not only contains the circuit but also comprises a magnetic circuit. When the transformer no-load closes or removal of external fault voltage recoveries, the transformer would produce several times rated current of the magnetizing inrush current. The inrush current would flow into the transformer differential protection circuit, which will result in malfunction of transformer protection. Therefore, this paper researches on how to identify and suppress the inrush current.On the basis of extensive reading of transformer magnetizing inrush current identification methods and suppress strategy, this paper put forward a reasonable classification and analyzes the advantages and disadvantages of them. In the aspect of inrush current identification, this paper builds a simulation model and obtains the waveforms of transformer magnetizing inrush and internal fault current. Based on this, we propose to identify inrush current by using wavelet transform. In order to improve the clarity of wavelet transform in the inrush current identification, this paper uses the ratio method to improve the wavelet transform and finally proves the correctness of this method in identifying inrush current through lots of simulation results.In addition, this paper studies the existing magnetizing inrush current suppression strategy and presents a series resistor capacitor switching technology. This method considers the variation of the magnetic core in the three-phase windings of switching, combines utility of series RC, and finally verifies that taking on simple strategy can effectively suppress the inrush current. This paper proves the effectiveness and practicability of the method through lots of simulation results.