Starting Current Analysis in Medium Voltage Induction Motors: Detecting Rotor Faults and Reactor Starting Defects

The failure of Medium Voltage (MV) induction motors is a major concern in the steel industry since it can cause an unplanned outage resulting in significant economic consequences. Predictive maintenance based on offline and online testing of the induction motors is critical for maintaining reliable, efficient, and safe plant operations. Many years of experience has indicated that the MV induction motor failure rate can be reduced with periodic motor testing, resulting in improved plant reliability and productivity. It has been observed that false fault indications are commonly produced by commercially available test equipment. Considering that the application of multiple types of tests can improve outcome reliability, the effectiveness of a new test approach based on the analysis of the motor starting current was investigated for detecting defects in the rotor cage and reactor starting. An analysis of the starting data obtained from 614-MV induction motors operating at a steel mill over the past 10+ years showed that these two types of faults were present in 45-MV motors. Five successful case studies of rotor cage and four cases of reactor starting defects are presented in this article to demonstrate the advantages of starting current analysis for induction motor monitoring.