Abstract : This paper introduces several main soft-start methods for high-voltage, high-capacity motors: autotransformers, hydraulic couplings, hydraulic resistance soft starters, and frequency converters, discussing their principles, advantages, disadvantages, and applications. The development trend of high-voltage motor starting is also analyzed. Keywords : High-voltage motor; autotransformer; hydraulic coupling; hydraulic resistance soft starter; high-voltage frequency converter 0 Introduction With the continuous increase in the scale and single-unit capacity of the metallurgical industry, the application of large high-voltage motors is also increasing, while the power system capacity has not increased proportionally. Direct starting of large high-voltage motors obviously has too great an impact on the power grid, affecting both the safe operation of the grid and the motor itself; it also causes significant damage to the machinery. Therefore, various soft-start technologies have emerged. This paper mainly introduces the principles, advantages, disadvantages, and applications of several soft starters. 1 Autotransformer 1.1 Working Principle Traditional stator series resistance or reactor starting results in excessive reduction of starting torque, suitable only for light-load starting. However, large high-voltage motors carry heavier loads. If the load is heavy, an autotransformer can be used for reduced-voltage starting. A three-phase Y-connected autotransformer is used. During starting, the three-phase coils of the autotransformer are connected to the power supply, and its secondary tap is connected to the motor, allowing the motor to start with reduced voltage. Once the speed reaches near steady-state, it switches to the normal operating position, and the motor operates at full voltage. The switching process is completed by a contactor. 1.2 Starting Advantages Compared to the starting method using stator series resistors (or reactors), the autotransformer has better current-limiting effect while obtaining the same starting torque; it can obtain a larger starting torque while maintaining the same current-limiting effect. Therefore, using an autotransformer for reduced-voltage starting can handle larger loads. The autotransformer reduced-voltage starting method is suitable for starting large-capacity motors, and the starting torque can be changed by altering the connection position of the taps to suit different loads. [b][align=center]For more details, please click: Starting of High-Voltage Motors[/align][/b]