Theory Research And Realization Of Numerical Transformer Protector Based On Wavelet Transform

With the development of economy in our country recently, there has been more and more requirement of power energy. The scale of power system is enlarged continually, so the function of transformer with large capacity in power system is more important, and there is some new requirement for the transformer protection. Differential protection is the master protection for the important power system elements such transformer, but magnetizing inrush current is still the primary reason that causes transformer protection miss-operating, so the discrimination between magnetizing inrush current and inner fault current correctly is the key that ensures transformer differential protection operating credibility.Magnetizing inrush current has obvious singularity that is intermission angle proving by some research, and wavelet transform has the ability of analysis for multi-scale and good time-frequency local characteristic, so it is particularly well adapted to extract the characteristic of signal's edge and peak break. This thesis chooses B spline wavelet that adapts to the analysis of power system signal, and uses the wavelet transformer to analyze the magnetizing inrush current and inner fault current. Base on intermission angle principle, a practical method was established, which avoids the disadvantage of the traditional method with accurate measurement of intermission angle, but only analyses the wave transformed from original signal after transform. This method is effect proved by the experiment base on DSP equipment, so it can be realized in the existing hardware. This thesis wrote wavelet transform program in C and Assembly program language with B spline wavelet.After the improved criterion and its arithmetic program in this thesis have been tested with real operation data, it has been proved that this criterion can distinguish between magnetizing inrush current and inner fault current correctly and fast.