Investigation of Broken Rotor Bar Faults in Three-Phase Squirrel-Cage Induction Motors

It is well understood that squirrel-cage induction motors are rugged, reliable, cheap, and thus widely used in industrial and manufacturing processes. However, electrical and mechanical faults pose a particular challenge to the industry and end users which often interrupts the productivity and requires maintenance. In literature, rotor faults have been shown to account for a large portion of induction motor failures, sometimes they are the single biggest cause of failure in the field. Rotor bar faults generally arise from repeated operating stresses which can be electrical, mechanical, thermal or environmental by nature. The causes of rotor bar and end-ring breakage include: (a) magnetic stresses caused by electromagnetic forces, (b) thermal stresses due to abnormal operating duty, including overload and unbalance, (c) inadequate casting, fabrication procedures or overloading, (d) contamination and abrasion of rotor because of poor operating conditions, (e) lack of maintenance. Most failures will increase the current and stress in the adjacent bars, progressively deteriorating the rotor part and degrading the motor’s overall performance. Without doubt, it is of great importance to appreciate the mechanisms and characteristic changes of broken bar faults. Furthermore, an online fault diagnostic system is highly desired to meet the reliability requirements, as well as reducing the costs of maintenance and increasing field efficiency.