Experimental Performances of Harmonic Current Sideband Based Broken Bar Indicators

Experimental work is presented in this paper, that clearly indicates the good behavior of some novel rotor bar fault indicators for converter-fed squirrel cage induction motors. The ratio of the fifth harmonic upper sideband on the seventh harmonic and the ratio of the seventh harmonic lower sideband on the fifth harmonic seem to be good broken bar indicators, largely independent on load conditions and drive inertia, and with sufficient rejection to frequency variations. We remember that classical indicators used in MCSA (such us the ratio of the first harmonic lower sideband on the first harmonic) depend heavily on those conditions. The relationship between the new fault indicators and the number of broken bars is quite linear, too. Harmonic current side-band based indicators (HCSBIs) have been previously derived by the authors from the multi-phase symmetrical component theory (MPSCT). Results of broken bar tests conducted on an experimental cage motor with variable fault gravity and load level have been reported and commented in this paper, for HCSBIs performance evaluation about fault severity assessment in case of broken bars.