Research On Transformer Longitudinal Differential Protection Based On Wavelet Analysis Method And Compensation Approach Of Secondary Current

Analyzed the existing problems of the transformer longitudinal differential protection in this paper. On the one hand, when external short-circuit fault, TA saturation current will cause imbalance current to cause and lead to the protection misoperation . Therefore using the wavelet packet analysis TA saturation second harmonic current characteristics, forwarded the function relation between second current distortion rate and TA current transformer error. Realizationed based on current distortion rate adaptive rate braking protection by this. Under the conditions of great current, it can make braking ratio more reasonable, so as to improve the sensitivity and the ratio of the differential protection reliability. On the other hand, analyzed the mechanism of generating transformer inrush current and the characteristics and identification methods. Pointed out the existing problems that baseding on the principle of the dead angle of excitation inrush current identification method in transformer microcomputer protection. To improve the accuracy of excitation inrush current recognition, according to the signal singularity detection theory of wavelet transform, analysised the simulation data that internal faults of transformer and excitation inrush current by choose MATLAB simulation tools and binary discrete wavelet function. Extracted the characteristics of excitation inrush current to establish a new identification method. This method has strong robustness for TA saturation, theoretical analysis and MATLAB simulation experiments indicated that the principle will not be affected by the TA saturation, simple and effective, and avoided the faults that hardware requirements of high and computation in the method of traditional accurate measuring the dead angle of excitation inrush current. At last, with core TA excitation inductance due to nonlinear characteristics, easy to cause the TA saturation, causing the protection and measurement cannot completely overcome the impact of TA saturation. Simulated current transformer by MATLAB, analysis of various factors affecting its saturation, and put forward a quadratic current compensation method that based on difference algorithm for excitation current.