Field simulation of linear induction machines illustrating the peak-to-peak ripple in propulsive force and its dependence on the length of the primary

In this paper, results of Finite Element Analysis of three Linear Induction Machines have been presented and compared. The three LIMs are identical in all respects except that the length of their primaries are different from one another. Due to magnetic asymmetry, it is noted that in all the LIMs, the induced EMF in the three primary windings have got unequal magnitude when supplied from a balanced three phase voltage source. This unbalance is reflected in the waveform of the Propulsive Force or Thrust. The thrust waveform shows a ripple component in addition to the average value. Since the ripple arises due to the magnetic asymmetry of the LIMs, the dominant frequency of the ripple is twice the supply frequency. It has been shown that in all the LIMs the amount of ripple increases with increase in speed of the machine. Also, for a given speed, the LIM whose primary is the longest has the lowest ripple component in its thrust.