Improved Rotor Bar Structure in High-Voltage High-Power Induction Motors to Eliminate Local Thermal Spot and Avoid Broken Bar faults

Due to complex harmonic field effect and frequently starting operation conditions, broken bars are the most common fault in practice, for instance, in the auxiliary motor systems in the power plant. To solve this problem, this paper proposes an improved rotor slot structure of large-power and high-voltage induction motors in the re-manufacturing process, for eliminating the local thermal spot and avoiding broken bars. This structure adopts a novel harmonic field slot to eliminate the skin effect caused by high-frequency harmonic fields, and the optimal design of slot size, opening width, and height, air-gap length based on finite element analysis (FEA) are performed to verify its effectiveness. Experimental validation is performed on a re-manufactured 6-kV 1600-kW induction motor in a thermal power plant in China. The results show that the presented design structure can eliminate the local thermal spot in rotor side and the measured thermal distribution in the surface of stator cooler can also be reduced by 18°C. The achievement of this paper can provide the technical support for countermeasure of broken bar fault in large-power and high-voltage induction motors.