Study On The Detection Method Of Inrush Current In Transformer

In recent years, the rapid development of the national economy Chinese, power surge,network scale is continually developing and expanding, the voltage level rising, Transformeris extremely important equipment to the power system, the safety and stable operation oftransformer supply reliability of overall power, which put forward higher requirements for theprotection of power transformers. Because inrush current will flow into the differential circuitof the transformer differential protection. If the inrush current cannot be identified, differentialprotection may wrongly operate. Therefore, how to effectively identify the magnetizing inrushand internal fault current that is an important and difficult problem.So,this thesis studies in thefollowing aspects.First of all, combined with the engineering practice, this paper studies the effects oftransformer excitation inrush current on security and stability of power system, brieflyreviews the domestic and foreign research status of inrush current,and analysis of the adverseeffects of magnetizing inrush current of transformer relay protection. To further improve theaccuracy of identification of transformer magnetizing inrush current, the continued study ofrecognition of inrush current is very significant and practical.Then,The generation mechanism of the field excitation inrush current is detailed researchedin this dissertation.The methods of inrush current identification is analyzed, and theiradvantages and disadvantages are researched. The difference between internal fault currentand magnetizing inrush is compared and analyzed. Feature information of internal faultcurrent and magnetizing inrush is discussed by using method of multi resolution analysis.Thirdly, on the basis of the above analysis, combining wavelet analysis and informationentropy theory, put forward method to identify inrush current of transformer based on Tsalliswavelet entropy （energy entropy and time entropy）, the procedure of this method is that thecurrent is decomposed and reconstructed,then using the concept of entropy to quantitativeanalysis of the distribution of the energy, and the Tsallis wavelet can largely improve theproblem of frequency aliasing and energy leaking. Therefore, this method can accuratelyidentify the excitation inrush current. But also, according to the instantaneous wattless powercharacteristics, another method based on instantaneous time active wattless power isproposed.,whose main principle is the difference between the transformer active and reactivepower on both sides. This method also can effectively identify excitation inrush current.The model of inrush current simulation is builded by Matlab/Simulink, the single-phasethree winding transformer and three-phase three winding transformer is verified by simulation under various fault conditions using the above two kinds of recognition methods, such asno-load closing, single-phase earth fault and fault clearing and restore the power supply andso on, the result of simulation shows that methods have good effect for recognition, whichverifies the feasibility and sensitivity of the two kinds of identification methods, whichovercomes the defects of the prior protection, improve the protection performance oftransformer differential protection.