Research On Air Gap Eccentricity Analysis And Fault Detection Effectiveness In Induction Motor

Electrical machine is a conversion tool between electrical energy and mechanical energy which plays an important role in manufacturing,life and scientific research.With the development of science and technology,the application of electric motors in new facilities such as high-speed rail,maglev trains and aircraft electromagnetic ejection devices is becoming more and more extensive.These applications provide comfortable,fast service and strong guarantee,and how to ensure the motor safe and reliable running has become an important issue for people to pay attention to.Air gap eccentricity fault is a very common fault in large-scale rotating electrical machines.It has always been one of the hot issues studied by experts and scholars in related fields at home and abroad.Improper installation,loose or missing bolts,misaligned shafts,unbalanced rotors,etc.can cause eccentric failures.In this paper,we will study the intrinsic relationship between air gap eccentricity and air-gap magnetic flux density in induction motor,the factors affecting the harmonic components,the influence of air gap eccentricity on the performance of the motor,the mechanical analysis of air gap eccentricity,and the effectiveness of eccentricity detection.The details are as follows:(1)The equivalent magnetic circuit diagram under eccentricity is established and the first-order rotor slot harmonic permeability is considered.Flux density harmonic components under non-eccentricity and eccentricity are analyzed.Besides,different parallel branches are considered in the harmonic analysis of air gap eccentricity in this paper.(2)In consideration of odd-order harmonic components brought by air gap eccentricity,the harmonic components are added to the analysis of stator winding loss and rotor winding loss.Among these,different parallel branches are considered in the loss analysis of air gap eccentricity.(3)Considering that the direction of flux at the yoke is uncertain and the direction of flux at the tooth is basically radial,flux density in the stator core are divided into two perpendicular dimensions,radial and tangential.A blocked and layered iron loss calculation model is established to provide a more accurate calculation method for iron loss calculation under eccentricity.(4)The principle of generating the average value and pulsation value of unbalanced magnetic pull is theoretically analyzed.The effect of the number of parallel branches,the number of rotor slots,the number of pole pairs,operating states etc.on unbalanced magnetic pull is studied.(5)In order to develop the study of axial non-uniform eccentricity,a threedimensional finite element model is established and flux density change in the axial direction of air gap under inclined eccentricity is analyzed.The influence of the offset of axial eccentricity on the performance of the motor is studied.(6)For a specific induction motor,the interference and effectiveness of eccentricity detection under diferent slot combinations is studied.Two methods based on harmonic detection and fundamental detection are proposed to judge the eccentricity type of the motor and predict its eccentricity degree.The research works in this dissertation lay a theoretical and technical foundation for fault analysis and fault detection of air gap eccentricity in induction motors.