What Is Wrong In Most Papers With The Equivalent Circuit For LIMs
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Jacek Gieras / UTP University of Sciences and Technology
The difference between equivalent circuits of cage induction motors (rotor with concentrated parameters) and single-sided LIMs with solid steel or Al cap over solid steel (reaction rail with distributed parameters) has been analyzed. In LIMs, both the resistance and reactance of the secondary circuit are functions of the slip and the magnetic field intensity. This results from the definition of the wave impedance of a solid conductive medium, i.e., the ratio of the electric component–to–the magnetic component of field intensities at the surface. The impedance of the reaction rail must be derived on the basis of the electromagnetic field distribution. Most authors make typical errors assuming that the reaction rail of a LIM with distributed parameters behaves similar to the cage rotor of an induction motor. Therefore, in most papers the same T-type equivalent circuit as for cage induction motors is applied to LIMs with distributed-parameters reaction rail. Although, the derivation of equation for the longitudinal end effect is complex, the longitudinal end effect can be simply included in the T-type equivalent circuit by introducing the so called “end effect impedance” in the vertical branch. Both equivalent circuits without and with the end effect taken into account have been considered.
