Study On Transformer Differential Protection And Inrush Current Identification

Transformer is an important power device in power system,which requires high stability of its operation.The main protection of transformer is differential protection,and there may be unbalanced current during its operation.In this case,the appearance of inrush current greatly affects the reliability of transformer differential protection action.Then the problem of identifying inrush current quickly and accurately becomes the first difficult problem in power grid operation and the focus of transformer differential protection device research.In this paper,an improved differentiator is introduced to identify inrush current by applying wavelet transform to transformer differential protection.The main tasks are as follows:The principle of differential protection of transformer and the unbalanced current generated in differential protection are analyzed,and the influence of excitation current on differential protection is explained.In explaining the causes of inrush current,special attention is paid to the study of how to determine inrush current,which is often used in differential protection,analyzes the strengths and weaknesses of existing methods,and provides theoretical support for further research.By analyzing the theoretical knowledge of wavelet transform,analyzing three common wavelet transform and Mallat fast algorithm,analyzing the application of wavelet transform in in inrush current recognition,the mean value of wavelet energy ratio can provide the basis for identifying inrush current.At the MATLAB/SIMULINK simulation platform,the inrush current and fault current are simulated in order to simulate the simulation model of power transformer and analyze the two current signals.Based on db4 wavelet transform,wavelet transform is used to simulate inrush current and fault current.It can be seen that wavelet coefficients can show various fault current and fault current characteristics characteristics of inrush current,and the wavelet energy ratio method can effectively distinguish the two,which provides data support for the next research.Finally,in order to reduce the time needed to determine the transformer differential protection to identify the inrush current,wavelet transform is applied to the inrush current detection,it is suggested that the improved differential tracker be included in the inrush current identification method of wavelet transform.This method can ensure the accuracy of wavelet transform under waveform fixed structure and improve the speed of waveformation after wavelet transform,which greatly speeds up the time of transformer protection in recognition of inrush current.By the same token,the MATLAB/SIMULINK model confirms the effectiveness of the method described in this paper.