Simulation of the bearing voltage in an inverter-fed induction motor by a full three phase multi conductor transmission line model

An accurate numerical model, based on multiconductor transmission lines (MTL) able to evaluate the voltage dynamics across the motor bearings and associated currents of an inverter-fed motor is presented. A full three phase stator winding of the wound type of a high power traction motor is considered in the proposed analysis. The different regions of the motor are modeled as suitable connections of lossy MTL which are then studied in the time domain. The per unit length characteristic matrices describing the MTL are accurately calculated by a FEM based software. The effects of the rise time of the input voltage and the length of the feeder cables are discussed. The reliability of the numerical results achieved by means of the MTL model is checked by performing a comparison with those obtained by considering a lumped parameter equivalent circuit.