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.