Analysis And Research Of The Power Transformer Inrush Current

The power transformer is one kind of the key electrical main equipment in Power System. Once fault was happened, which will be able to bring about very big economic losses. Differential protection is the master protection for transformer all along, long-time running experience indicates that differential protection can be sensitive to distinguish between an external faults and Internal faults, but we connect a transformer to the system without load or remove its external faults ,it will bring magnetic inrush current that leads to miss-operation of the differential protection. So distinguishing inrush current correctly is the key to ensure transformer differential protection to operate credibly.This paper studies on some problems of power transformer inrush current, and analyzes the fundamental cause and characteristic that it produces, and studies major methods that distinguish between inrush current and internal fault currents . and establishes simulation signal model for inrush current and fault currents by the simulated PSCAD/EMTDC software platform, and extracts the representative inrush current and internal Fault current signal sample, Then we process the data with Wavelet analysis methods. This thesis chooses DB wavelet that adapts to the analysis of power system signal, and uses the wavelet transform to identify the magnetizing inrush current and inner fault currents. That makes use of the wavelet analysis to check characteristic property, and discusses characteristics of the singularity. A criterion for identification of magnetizing inrush current is designed, this paper develops a system for distinguishing inrush current based on VC++ platform.It shows that the criterion can correctly distinguish between magnetizing inrush current and internal fault currents in the experimental environment. This criterion provides a reliable blocking for transformer protection, and has some practical value. In view of the complexity of inrush identifying, this criterion also requires a step further testing in practice.