High frequency modeling for cable and induction motor overvoltage studies in long cable drives

High frequency simulation models for power cables and motors are the key tools that aid a better understanding of the overvoltage problem in PWM drives with long feeders. In this paper, the frequency responses of the cable and the motor windings are obtained experimentally and suitable models are developed to match the experimental results. Several lumped segments incorporating a lossy representation of the line is used to model the cable. The cable and induction motor models may be implemented using a computational tool such as Matlab, thereby providing a convenient method to analyze the overvoltage phenomena. Simulation and experimental results are presented for a typical 3 hp induction motor, showing the suitability of the developed simulation models. The most promising dv/dt filter networks are also investigated through simulation analysis, and a design approach based on a trade off between filter losses and motor peak voltage is proposed. Experimental results of an RC filter at the motor terminals demonstrate the validity of the simulation models.