Research On Analysis And Suppression Method Of Transformer Magnetizing Inrush Current

Transformer magnetizing inrush current may not only cause malfunction of relay protection devices,but also jeopardize the stability of power system operation.This thesis analyzes the transformer no-load reclosing process,and proposes an inrush identification method based on average equivalent inductance parameter as well as a phase selection closing strategy based on residual flux detection.The work of the dissertation helps to improve the effect of identifying and suppressing inrush current in the power system reclosing device,and has some engineering application value.Firstly,this thesis analyzes the damage of transformer inrush current,clarifies the mechanism and influencing factors of inrush current,introduces the main recognition methods and suppression methods of inrush current,and analyzes the effects and problems of each scheme.Secondly,the equivalent circuit and voltage equation of no-load transformer under reclosing operations of power system are analyzed,and the influence of various factors such as the number of closing phases,the connection mode of power system,and the transformer wiring group are fully considered.An identification method of magnetizing inrush current based on average equivalent inductance parameter is proposed.This method can accurately discriminate the inrush current of no-load transformer during the reclosing process of power system,and avoid the misinterpretation of transformer inrush current as a short-circuit fault.Then,based on magnetic domain theory and the hysteresis characteristics of ferromagnetic materials,the cause of transformer core remanence is explained.A method for detecting core remanence value using Hall sensors to detect the transformer leakage magnetic field is proposed.This method is applicable to different kinds of transformer core structures.A three-phase threecolumn transformer is modeled by Maxwell,a finite element analysis software,under different remanence conditions.The comparison between the simulated measurement and the fitted calculation validates the feasibility of transformer core residual magnetism measurement method based on magnetic flux leakage detection.Finally,a phase selection closing strategy based on remanence detection is established to suppress inrush current.Since linear inductance model of transformer iron core can not describe the initial remanence condition of the three-phase transformer,an iron core hysteresis model is established and the corresponding mathematical expressions are derived.According to the change rules of three single-phase transformers and three-phase three-column transformer closing flux in neutral point ungrounded system and neutral point grounding system,phase selection closing strategy for suppressing inrush current of these two kinds of transformers is established.The simulation analysis of examples shows that phase selection closing strategy can effectively suppress the transformer magnetizing inrush current.