Determining the optimal technique for early detection of broken rotor bars in medium voltage squirrel cage induction motors during operation

摘要

Electric motors play a pivotal role in various industrial plant processes forudelectrical to mechanical energy conversion. As a result their reliability andudavailability is of utmost importance to industries. The reliability and availability ofudplant electric motors can be achieved by early detection of any developing faultudby performing condition monitoring and preventative maintenance on motors.udAn important motor failure mode, which has been quite challenging to detect, isudcracking and subsequent breaking of rotor bars in induction motors.udThe existing condition monitoring techniques are incapable of positively detectinguda cracked or single bar problem during operating conditions. Bars have broken,udlifting out of the rotor slots and damaging all stator coils, consequently forcing theudremoval of the motor during plant operation and a complete rewind of the stator.udThis research is being conducted to ascertain, from existing conventionaludtechniques, an optimal technique for the detection of a cracked rotor bar or audcompletely broken single rotor bar in induction motors under operatingudconditions. Furthermore, it explores non-conventional techniques, which canudassist in detection of broken rotor bars.udThe report starts by presenting the literature on stator current and axial vibrationudanalysis which are conventional rotor bat detection techniques. Thereafter, theudMaxwell 2D simulation results which indicate stator current broken rotor baruddetection frequencies are discussed, followed by the experimental measurementudresults and discussions. The conclusion drawn from the experimental results isudthat the stator current analysis is, presently, the optimal technique to detect audsingle broken rotor bar during a medium voltage induction motor operation. Theudaxial vibration analysis is recommended as a secondary monitoring technique toudsolidify the stator current diagnosis. The shaft voltage analysis is introduced as audnon-conventional technique and the shaft voltage results are discussed.