On Shortening the Numerical Transient in Time-Stepping Finite Element Analysis of Induction Motor Under Broken Rotor Bar Faults

In induction motors, broken rotor bar faults are common and represent an aggressively propagating phenomena in applications in which motors are subject to frequent line starts and stops. Fast and accurate analysis of induction motors under this type of faults is desirable. Time-Stepping Finite Element (TSFE) analysis of induction motors, as one of the most powerful tools of analysis, suffers from the lengthy numerical transient response and the large number of ac cycle periods that are needed to reach a steady-state level of flux build-up. That is, until a steady-state solution is reached. In this paper, this lengthy and undesirable transient time, as an obstacle, was successfully reduced through the implementation of the so-called "Virtual Blocked Rotor (VBR)" approach described in this paper. The VBR approach starts by determining motor permeabilities and skin effect corresponding to the operating condition of the induction motor. Permeability computation is performed in an FE Eddy-Current frequency-domain solver with the desired voltage supply magnitude and frequency, slip, and given broken rotor bar pattern. The computed permeabilities are then imported into the TSFE simulation model of the faulty induction motor and the performance criteria of interest are extracted for further evaluation. In this paper, a four adjacent broken bar fault pattern is studied in the given case-study induction motor. It was observed that this approach successfully and substantially mitigates the problem of the lengthy numerical transient response to reach a steady-state solution, and hence saves a large amount of time in the computational process.