Field Analysis and Equivalent Circuit Parameter of Eddy Current Rotor Induction Motor With, Without and Closed Iron Backing

Abstract

An eddy current rotor consists of a continuous conducting medium so that, the rotor current can be flow anywhere within the non-magnetic isotropic, conducting cylinder which may be hollow. The eddy current rotors for induction machines come in a variety of structures with, without and closed iron backing. The eddy current rotor without iron backing, fulfill many restrictions like having minimum weight, simplicity in construction and reliability in operation. The most important features that this machine must have are the linearity of its output characteristics and a small time constant.

This paper presents the magnetic field analysis of the eddy current rotor induction motor with applying the two-dimension field analysis. The analytical treatments are based on the solution of the derived field equations with suggested boundary conditions. This analysis carried out using the magnetic vector potential, which can be readily adaptable in evaluation of the magnetization impedance for many rotor constructions. The magnetic vector potential enables the effect of physical air-gap with finite permeability and conductivity of machine regions to be taken into account. Using a new technique, the complex equation of the magnetization impedance can be simplified to predict closed forms for the individual equivalent circuit parameters. In this paper, the expression of the air gap impedance is modified and rearranged to give the individual rotor resistance, leakage reactance and the rotor to stator mutual reactance. These closed forms are carefully arranged for perfect results with minimum calculation effort. Results calculated here with using this analysis, are in closed agreement with those obtained experimentally.