Transverse edge effects in linear induction motors

Currents in the secondary member of a linear induction motor flow in roughly elliptical paths. The secondary appears to have a resistivity greater than the natural value, and the cross-gap flux density peaks towards the edges of the stators. This phenomenon is known as the transverse edge effect. In most previous work, the edge effect has been allowed for only by the use of a resistivity-increase factor. This paper gives a more exact treatment. The method used takes account of flux leakage in the space between the stators and the secondary member, and in the secondary itself. Some approximation is necessary in the treatment of the machine end-turn flux. Equations are derived for the flux-density distribution in the air gap and for thrust, in each case as a function of stator current. Static-field measurements on two linear induction devices of different design, and with secondaries of different materials, showed good correlation for the two frequencies used, except at the extreme edges. In a simulated dynamic test using a rotary machine, calculated and measured field distributions and forces agreed well over the whole slip range