Development of a tool to detect faults in induction motors via current signature analysis

This paper demonstrates through industrial case histories, how current signature analysis can reliably diagnose rotor cage problems in induction motor drives. Traditional CSA measurements can result in false alarms and/or misdiagnosis of healthy machines due to the presence of current frequency components in the stator current resulting from nonrotor related conditions such as mechanical load fluctuations, gearboxes, etc. Theoretical advancements have now made it possible to predict many of these components, thus making CSA testing much more robust and less error prone technology. Based on these theoretical developments, case histories are presented which demonstrate the ability to separate current components resulting from mechanical gearboxes from those resulting from broken rotor bars. From this data, a new handheld instrument for reliable detection of broken rotor bars, air gap eccentricity, shorted turns in LV stator windings and mechanical phenomena/problems in induction motor drives is being developed and is described. Detection of the inception of these problems prior to failure facilitates remedial action to be carried out thus avoiding the significant costs associated with unexpected down time due to unexpected failures.