Transformer Microcomputer Protector Based On Wavelet Theory

With the development of economy in our country recently, there has been more and more requirement of power. The size of power system is enlarged continually, so the function of large transformer 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 all through, but magnetizing inrush current is still the primary reason that causes transformer protection miss-operating, so distinguishing between magnetizing inrush current and inner fault current correctly is the key that ensuretransformer differential protection operating credibility.Magnetizing inrush current has obvious singularity, and wavelet transform hasmulti-scale and good time-frequency local characteristic, that it is particularly well adapted to extract the characteristic of signal's edge and peak value, and can check up the singularity well. 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. A transformer microcomputer protection was designed in this thesis, and in the base of intermission angle principle, a new criterion was established, which pierces through the traditional method with accurate measurement of intermission angle, but analyses the wave by wavelet transform. This criterion is lower in hardware, so it will be realized in the existing hardware. This thesis edited wavelet transform program with B spline wavelet.After the new criterion and its arithmetic program in this thesis have been tested with now experimental data, it has been proved that this criterion can distinguish between magnetizing inrush current and inner fault current. When intermission angle may be vanishing in TA saturation, the new criterion can also distinguish correctly without module that makes the vanishing intermission angle. In conclusion, this criterion has applied value.