Research On Strand Current Measurement And Strand Fault Diagnosis Method Of Stator Bar In AC Electrical Machine

AC electrical machine is one of the important equipments of power system and electric drive system.With the growing capacity of AC electrical machine,the stator bar,as the core of AC electrical machine,directly determine the safety and service life of AC electrical machine.With the development of stator bar transposition technology,higher requirements are put forward for the transposition process and production quality of stator bar.Due to the tight compact structure of the strands in stator bar,it is difficult to directly evaluate the effectiveness of transposition type and the quality of stator bar.To solve these problems,this thesis studies the strand current measuring method of stator transposition bar,electromagnetic calculation of typical strands short-circuit fault,strands short-circuit fault characteristic and the fault diagnosis method.According to the distribution of end leakage magnetic field of stator transposition bar,the strand current measuring method for the stator transposition bar by end leakage magnetic field is proposed.The analytical model of strand current measuring method is established,and the searching coil array is designed for end leakage magnetic field measurement.The strand current approximation algorithm based on least square error function is used to solve the strand current,where the traditional methods cannot solve the equation with the limited range.The proposed method measuring results are compared with traditional current transformer measurement results,and the rationality and the validity of proposed method is validated.It provides a new measuring method for the electrical test of stator transposition bar and the research of strands short-circuit fault.The insulation of the transposition strand is easily damaged at the transposition bend due to the stretching stress,which causes strands short-circuit in the stator transposition bar.In view of the strands short-circuit fault cannot be calculated by numerical method owing to the crossing of short-circuit strands,the three-dimensional multi-segment field-circuit coupling restraint method for the strands short-circuit fault in stator transposition bar is proposed,which contains the whole stator bar end and the radial spatial position of strands.The modeling process is simplified by the coupling restraint circuit simulates the strand transposition path.With the field-circuit coupling method,the numerical calculation of the strands short-circuit fault of stator transposition bar is realized.The problems of physical modeling and numerical calculation of the stator bar with complex transposition structure is solved.The accuracy of the proposed method for the numerical calculation of stator transposition bar and the strands short-circuit fault are verified by comparing the calculated results with three-dimensional finite element method and experiment.The electromagnetic and thermal characteristics of the strands short-circuit fault in stator transposition bar are researched.The short-circuit fault schemes of Roebel transposition stator bar with different positions and different short-circuit types are designed,and the strand current,end leakage magnetic field and strand temperature rise of the fault schemes are calculated and analyzed.The electromagnetic features of strands short-circuit are defined by studying the effect of strands short-circuit fault on the electromagnetic thermal characteristics of the stator transposition bar.The inherent relationship between the electromagnetic features and the strands fault position are analyzed.It provides a theoretical reference for the fault diagnosis of the strands short-circuit in stator transposition bar.The strands short-circuit fault feature and the strands short-circuit fault diagnosis method of stator bar are reseached.By analyzing the coupling relation between the strand current of stator transposition bar and slot leakage magnetic field linked by strands,the unbalanced slot leakage magnetic flux as strands short-circuit fault feature is proposed.The strands short-circuit fault estimation model of the Roebel transposition stator bar is established by using the strands short-circuit fault feature.This thesis introduces the adaptive end leakage magnetic flux density jump energy function according to the end magnetic field characteristics of strands short-circuit fault,proposes the identification criterion of strands short-circuit fault.Then,based on the mapping relationship between the short-circuit strands and the transposition path,and the coupling relationship between the fault feature and the end magnetic field of stator transposition bar with strands short-circuit fault,the fault location method for strands short-circuit fault in stator transposition bar is proposed.The diagnosis of serious strands short-circuit fault can be achieved quickly.