Design Of 2P Medium-sized Induction Motor With Variable Frequency Drive

2P induction motor has significant advantages such as high speed,large power density and low inertia.The drive system is more efficient and reliable when it is directly connected with high speed load.2P induction motor has simple squirrel cage rotor and good balance which are suitable for continuous running under high speed and high temperature conditions.With the development of electronic technology,the induction motor with variable frequency drive(VSD)has been used widely in the industry production.The vibration problems are always prominent among 2P medium-sized induction motors with VSD.The vibration can be divided into electromagnetic vibration and mechanical vibration according to different exciting forces.Electromagnetic forces are the source of electromagnetic vibration,while bearing problem or rotor unbalance are the main mechanical vibration reasons.Vibration investigation and reduction are very important for 2P medium-sized induction motors with VSD.In this paper,a 50 Hz Direct On line(DOL)2P motor is modified to apply to VSD use.The main work could be list as follows:(1)Reducing vibration which is the main motor design problem existing in the VSD application is described.Two preliminary motor designs are worked out considering the electromagnetic load and the approximate critical speed.They are prototype A and prototype B.(2)The radial electromagnetic forces and corresponding harmonic components in the air gap are analyzed by analytical method(AM).A proper slot combination is selected to avoid tooth harmonic electromagnetic forces.The flux densities are calculated by finite element method(FEM)and limited to reduce electromagnetic exciting forces.(3)The first order critical speed is calculated with approximate formula to get preliminary prototype design,and the first several orders critical speeds are calculated by experience formula method to avoid resonance according to American Petroleum Institute API541.The symmetric cooing structure of prototype B and its strengths are analyzed qualitatively.The shield rigidity and frame rigidity are increased to make the natural frequency of the whole motor much higher.(4)The prototype B is selected as the optimized design of 2P induction motor with VSD and manufactured in the factory.The feasibility of the design concept and calculation method in this paper are proved according to the results and analysis of test data.