A comparison of two and three dimensional analysis of linear induction machines

The effectiveness of two- and three-dimensional models of linear induction motors are examined numerically. Consideration is given to the two-dimensional analysis with two different representations of the magnetic circuit, one where no field exists outside the air gap, and a second where the iron is extended to cover the secondary. It is shown that inclusion of an extended magnetic field in terms of three vectors reduces the thrust predictions. Furthermore, an investigation of representations of the fringing of the magnetic field along the motor sides revealed that as soon as normal forces are considered, the field fringing becomes larger than formerly expected, although two-dimensional analyses can give satisfactory results. The three-dimensional analysis is based on a Fourier expansion of the primary current density, and shows that harmonics in the system compensate each other