Influence of High-Frequency Impulsive Voltage on End-Winding Corona Protection Systems in Medium-Voltage Inverter-Fed Motors

End-winding corona protection technology is one of the critical design aspects for insulation systems in motors with rated voltages exceeding 3000 V. Previously, related studies globally have primarily focused on materials, simulations, and testing methods of corona protection structures for generator windings and stator bars under sinusoidal voltage conditions. However, as an increasing number of motors are driven by inverters, end-winding corona protection structures face complex high-frequency pulsed voltages instead of traditional sinusoidal voltages. This new operating condition introduces higher demands on the design and testing of end-winding corona protection systems. This study designed two typical end turn grading structures and established a repetitive pulse experimental platform featuring adjustable rise time. Experimental and simulation investigations were conducted on both end turn grading configurations. The results demonstrate that the temperature rise at the winding end as the voltage rise time decreases. Furthermore, an increase in frequency leads to a reduction in the impedance of the stress grading system, resulting in increased power dissipation and elevated temperatures. Finally, by comparing different voltage magnitudes, it was confirmed that the voltage step magnitude is the critical factor influencing the temperature rise at the winding end. These findings provide significant theoretical reference and practical guidance for the optimized design of end corona protection structures in large variable frequency motors.