Understanding the Fundamentals of Motor Current Signature Analysis

Motor current signal analysis is a method to perform on-line monitoring of the condition of electrical motors by examining the spectrum of the residual current of the motor for sidebands around the main frequencies. The interpretation of these spectra would be improved by having a physics based understanding of how particular perturbations appear in a spectrum. This report considers two possible models for an induction motor and its residual current. The first model uses the Steinmetz equivalent circuit, a standard model from the literature. The second model is derived from first principles based on Faraday and Ohms law and the conservation of angular momentum. It is able to capture the coupling between the rotor dynamics and the residual current. Some initial results are given for both models using a combination of asymptotic and numerical techniques.