Differential Protection Of Transformer Based On Improved Wacelet Theory

The five organic parts of power generation,substation,transmission,distribution,and users form the power system.Because power transformers are a vital electrical component in power systems.If the power transformer fails,it will have a major impact on the safe operation of the power system and reliable power supply.Therefore,in order to ensure the safe operation of the power transformer,and to prevent the accident from continuing to expand,it is imperative to install a relay protection device for the power transformer.Since the principle of differential protection is based on the comparison of the magnitude and phase of the current on each side of the power transformer,this comparison will be affected by the current transformers on each side of the power transformer and many factors.When the power transformer is in normal working operation and external fault,the unbalanced current in the differential protection circuit of the power transformer allows the differential protection to work under adverse conditions.In order to ensure that the correct and sensitive action of the differential protection of the power transformer is guaranteed,it is necessary to analyze the cause of the unbalanced current in the differential protection circuit,and take improvement measures according to the research conclusion,and finally eliminate it.Based on the wavelet theory,this paper improves the differential protection of power transformers and has carried out the following work.Firstly,the working state of the power transformer is analyzed to understand the impact of the power transformer under abnormal operation or fault operation.The magnetic saturation characteristics of power transformers are discussed to identify the inrush current of power transformers,including the principle,characteristics and influencing factors.The existing excitation inrush current identification methods are compared from different angles,and the typical methods such as second harmonic,discontinuous angle principle,waveform symmetry principle,wavelet transform and neural network are analyzed and evaluated.The basic principle of differential protection of power transformers and measures to prevent misoperation of differential protection of power transformers are studied.Secondly,based on the analysis of the inrush current characteristics,the difference between the fault current and the fault current is judged.The transformer simulation model is built for the magnetizing inrush current and the fault current by MATLAB software,and the various states of the transformer are simulated and analyzed.According to the powerful time-frequency local processing ability of wavelet,the wavelet transform theory is analyzed.The db4 discrete wavelet transform is applied to the magnetizing inrush current and various fault currents.The simulation analysis shows that the results can correctly reflect the state of different magnetizing inrush currents of the power transformer,and provide data support for further research.Finally,a method based on wavelet transform theory to improve the differential protection of power transformers is proposed.The wavelet coefficients of the high-frequency components after wavelet transform are used for various currents,and the excitation current is identified using a classification algorithm based on an extreme learning machine.The simulation results show that the proposed classification algorithm has fast convergence and accurate recognition.