Study On The Magnetic Properties Of Magnetic Materials For Electric Locomotives Under Actual Working Conditions

The core materials of electromagnetic equipments used for electric locomotive such as high frequency transformer,traction transformer and traction motor are usually composed of magnetic materials such as electrical steel sheet,amorphous alloy,nanocrystalline and so on.With the continuous complexity of the running environment of railway catenary,the core materials of all kinds of electromagnetic equipments work more frequently under the non-standard magnetization conditions such as harmonic and high frequency,which results in the increase of core loss,and noise,and the decrease of operation efficiency.Due to lack of experimental data on the complex magnetic characteristics of electrical steel sheets under non-standard magnetizations,the alternating magnetization curves and loss data are still widely employed to evaluate the devices' electrical and magnetic performance with limited accuracy.In order to realize the accurate modeling for loss and magnetostrictive characteristics of core materials under non-standard magnetizations,in this thesis,the testing and modeling of magnetic properties of magnetic materials for electric locomotives under actual working conditions,including hysteresis,loss and magnetostrictive characteristics,etc.,were studied.The research results are applied to the design of medium and high frequency transformers for electric locomotives,which lays a foundation for the design and operation of high efficiency,low noise and light weight of electric locomotives.This thesis mainly includes the following aspects:The first part,by considering such actual working conditions as harmonic alternating and distortedly rotating magnetizations for traction transformers and traction motor cores,based on experimental data of magnetic characteristics in an electrical steel sheet,a nonlinear harmonic alternating loss model was established by taking the weight of each harmonic into account.The harmonic weight coefficient was introduced to correct the traditonal simplification model,in which the total loss was summarized from the linear superposition of different harmonic loss,and the magnetization angle parameters was added to consider the anisotropic loss characteristics of electrical steel sheet.A rotational loss model based on the orthogonal decomposition method with variable coefficients was proposed by considering magnetization trajectories,in which the hysteresis coefficient and abnormal loss coefficient were expressed as functions of rotation magnetization trajectories.Further,in view of the complexity and diversity of distorted rotational magnetizations,it was difficult to carry out experimental measurements about different distorted magnetization loci.As a result,a distortedly rotational loss calculation model was presented in this thesis based on the derivation from the mathematical expressions of hysteresis loss,eddy current loss and abnormal loss by taking instantaneous distorted flux densities into account.By comparing with the experimental results,the effectiveness of models proposed above was verified,the modeling accuracy of loss models under harmonic alternating and rotating conditions was improved,and its ability to the engineering application was intensified.The second part,for the intermediate frequency transformers of electric locomotive running under the square wave excitation in a few kilohertz,the loss characteristics of such ferrite,amorphous and nanocrystalline as intermediate frequency core materials under square wave excitation were tested.The test results show that the core loss caused by square wave excitationsis obviously greater than that from sinusoidal wave.The Steinmetz loss correction formula with variable coefficients under square wave excitationswas proposed,in which the magnetic density amplitude B in the traditional Steinmetz loss formula was replaced with the flux density variation d B/dt and the coefficients and exponential parameters of equivalent frequency were expressed as a function of magnetization frequency.The nonlinear loss characteristics corresponding to different frequencies were indicated.Compared with the experimental results,the validity of the modified formula was verified and the calculation accuracy of high frequency core material loss was improved.The third part,aiming to the main reason causing the noise of intermediate and high frequency transformer,the magnetostrictive characteristics of amorphous strip and electrical steel sheet were measured and compared.The test results show that the amount of magnetostriction in an amorphous alloy strip is at least ten times greater than that of electrical steel sheet which will result into serious vibration and noise.Based on the nonlinear characteristics of magnetostriction in the amorphous strip,a magnetostrictive prediction model was established by introducing variable magnetostrictive coefficients to modify the linear piezomagnetic equation.The noise generated by magnetostriction in the amorphous alloy strip at different frequencies and magnetization intensities was calculated according to the formula of A-weight velocity level.The fourth part,the core model made of amorphous alloy for the intermediate frequency transformer of electric locomotive was designed and made,the experimental test system of core loss and no-load vibration noise was built,and the measurement of core loss,vibration acceleration and noise was carried out.In comparison with the no-load loss test results,the effectiveness of loss model proposed above was further verified.Based on the nonlinear piezomagnetic equation of magnetostriction in the amorphous alloy,the no-load vibration acceleration and noise of the core were simulated.By comparing with the test results,the noise simulation results is lower,and a correction coefficient of noise simulation is suggested,which provides a reference to the optimization design of intermediate and high frequency transformers.