A novel technique for detecting unbalance condition of the stator currents drawn by a squirrel cage motor

The aim of this work is to provide an alternative that could replace the conventional technique based on the spectral analysis of the line current to detect an unbalance state due to a weak amplitude drop affecting one of the three-phase currents drawn by a squirrel cage motor. From a theoretical investigation, it has been stated that the spectral analysis of the emf induced at the terminals of a simple search coil placed close to the motor frame may be of interest for diagnosis purpose. The experimental results have revealed that this suggested sensory signal provides an excellent fault indicator regardless of the load level.