Study On Eddy Current Loss,Temperature Rise And Electromagnetic Force In High-Speed Induction Motor Rotor

Compared with traditional induction motors,high-speed induction motors are widely used in large-scale high-speed centrifugal compressors,large-scale air cycle refrigeration systems and petroleum industries because they can be directly connected with high-speed loads and eliminated the need for mechanical speed-increasing devices with high noise level,big volume and high cost of operation such as gearboxes.However,the rotor structure of high-speed induction motors is quite different from that of traditional induction motors,because the rotor speed and stator winding current frequency of high-speed induction motors are very high.In order to improve the reliability of high-speed induction motors rotor,usually,rotor of high-speed induction motors is made into solid structure or corresponding to topological structure.No matter which structure,it makes electromagnetic field distribution of rotor very complex,which undoubtedly brings great difficulty to accurate analysis and calculation for rotor eddy current loss.In addition,the rotating magnetic field in air gap produces large eddy current and eddy current loss in solid rotor,which result in high temperature rise and large electromagnetic force in rotor.A megawatt high speed induction motor is taken as an example in this paper,firstly,the calculation method of rotor eddy current loss is studied,secondly,the temperature rise distribution and electromagnetic force of rotor are analyzed and calculated.Considering the advantages of analytical method with simple calculation process and finite element analysis method with high accuracy,a semi-analytical method for calculating eddy current loss in rotor is proposed.Firstly,the analytical formula for calculating eddy current loss in rotor is derived based on Maxwell equations.Secondly,the two-dimensional eddy current field finite element analysis method is used to calculate the magnetic field distribution of rotor.The eddy current loss in rotor is calculated,and compared with the calculation results of two-dimensional transient field finite element analysis method to verify the accuracy of the semi-analytical method.On the basis of the calculation results of rotor eddy current loss,the temperature rise distribution of rotor is calculated by finite volume method.For the axial sectional type radial ventilation system designed in this paper,the fluid distribution in air gap and stator radial ventilation ditch have a great influence on the fluid distribution of rotor,and then affect the temperature distribution of the rotor.Therefore,this paper first makes a coupling calculation of the temperature-fluid field in the whole machine,and emphatically analyzes the temperature rise distribution of rotor.On the basis of the analysis,the influencing factors of rotor temperature distribution are further studied.Based on the calculation results of transient electromagnetic field and the electromagnetic force mathematical model of rotor,the electromagnetic force distribution of rotor is obtained when the motor is running under rated operating condition,and the electromagnetic force distributions in regions with large rotor eddy current and magnetic flux density values are studied.