An experimental approach for diagnosis of adjacent and nonadjacent broken bars in induction motors at very low slip

This paper proposes an experimental approach for diagnosis of adjacent and nonadjacent broken bars in induction motors, particularly in low-load and absolute no-load conditions, since it is very difficult to detect broken bars when the motor is operating at very low slip or under no load, using the traditional current signature analysis method. This study took into account the use of Fast Fourier transform to analyze the resultant magnetic flux density in a low-cost Hall Effect sensor installed between two stator slots. The amplitudes of harmonic components have been evaluated, in order to identify adjacent and noncontiguous breakage bars around the rotor structure. Experimental results obtained on a 7.5kW squirrel cage induction motor are presented and discussed.