Improved Rotor Bar Shape in High-Voltage Large-Power Induction Motors to Eliminate Hotspot and Avoid Broken Bars

Due to the complex harmonic field effects and frequent starting, broken rotor bars (BRB) caused by hotspots at the rotor slot openings are the most common fault in high-voltage and large-power induction motors (IMs) applied to the auxiliary systems of the power plant. This article proposes an improved rotor bar shape of large-power and high-voltage IMs to eliminate the hotspot and avoid the BRB. With the presented rotor bar shape, the skin effect caused by the high-frequency harmonic fields can be weakened effectively. The optimal design of the presented rotor slot shape, the width and height of the slot opening, as well as the air-gap length are also performed by finite-element analysis to achieve the best operating performance of IMs. A 6-kV 1600-kW IM was remanufactured according to the optimal design and applied to the circulator pump in a thermal power plant. The test results showed that the stator winding temperature of the IM was reduced from 80.7 to 62.1 °C; meanwhile, the surface temperature of the motor cooler was also reduced obviously.