Upstream Impedance Diagnostic for Three-Phase Induction Motors

This paper presents a simple method of diagnosing the upstream impedance of a three-phase induction motor by analyzing the across-the-line startup current and voltage time-waveforms. Thermography is currently the only industrial method capable of detecting upstream contact resistance problems, but it requires line of sight to the location of the problem. The proposed method does not have this drawback. The accuracy of the resistive unbalance threshold settings used with muOmega-meters to diagnose downhill contact resistance issues in industrial settings was exceeded with the proposed methods in a laboratory implementation.