Research On The Influence Of Eddy Current Induced In Steel Rails On The Levitation Force Of A Maglev Train

Non-laminated steel rails are normally used in low-speed EMS (Electromagnetic Suspension) maglev systems and consequently eddy currents are easily induced in rails by moving magnets. The induced eddy current weakens the magnetic field in the air-gap and decreases the levitation force, particularly near the leading end of the magnet,and it decreases the levitation force as the increase of the vehicle speed. The eddy current also generates a drag force against the propulsion generated by the linear induction motor (LIM). The analyse of the eddy current problem and experiments were taken. The major work done in this thesis is listed below:Firstly, analytical and numerical analyses of the eddy current problem in the maglev rails are presented in this paper. The results indicate that:the eddy current density increases with the vehicle speed; the distribution of air-gap flux density may be disturbed by the eddy current effect;higher vehicle speed leads to a reduction of air-gap flux density in the front end area and an increase of air-gap flux density in the back end area of the electromagnet; as a result, it leads to a weaker air-gap flux density in average; the levitation force decreases with the vehicle speed because of the eddy current; parameters such as the length and the width of the electromagnet, the thickness of the rail,the suspension gap,etc, affect the speed characteristics of the electromagnet.Secondly, a permanent magnetic circuit is designed for compensating the influences of eddy current. The permanent magnetic circuit includes a yoke and a permanent magnet which are designed in U-shape, and to reduce weight and the cost, the permanent magnet works in the maximum energy point by optimizing the size of the permanent magnet. The simulation indicates that the designed permanent magnetic circuit can effectively weaken the influence of the eddy current on the levitation force.Finally, experiments are undertaken on the low-speed maglev vehicle, CMS-04, in Tangshan test line. Qualitative and quantitative analyses on the eddy current effect are made utilizing the experimental data gathered by the levitation monitoring and data acquisition system. Experimental results indicate that the eddy current reduces the levitation force of the electromagnet, which proves the validity of the theoretical analysis on the eddy current problems.