Multiconductor transmission-line model for the line-end coil of large AC machines

This paper describes how the PE2D finite-elements field package is used to calculate the distributed L and C parameters of a multiconductor transmission-line model for the line-end coil of a large AC motor. Under steady-state AC conditions, the package produces field distributions from which self and mutual inductances and capacitances can be calculated. Distributed shunt and series losses are included in the model, and there is no need for any assumptions about surge velocities in evaluating the coil response. Separate parameters are calculated for the slot and overhang regions and the various sections of uniform multiconductor transmission lines are joined in series to represent the complete coil. The coil response is then computed using a Fourier transform technique. The input waveform is broken down into its spectral components and the steady-state transmission-line equations are solved at each component frequency. The response at each frequency is then used in the inverse Fourier transform to arrive at the solution in the time domain. Responses calculated from the model are compared to test responses on a laboratory model of the line-end coil and are found to be in good agreement. Several parameter variations are then investigated on the theoretical model.