What is a soft starter and how does it work?

Soft starter is a motor control device that integrates motor soft start, soft stop, light load energy saving and multiple protection functions. It protects the motor and the power grid by adjusting the amount of current supplied to the motor to prevent excessive surge current when the motor starts, thereby improving the efficiency and safety of the system.

Contents

Working Principle

Starting Mode

Application Scenarios

Working Principle

The working principle of the soft starter is based on three-phase anti-parallel thyristors (SCR or silicon-controlled rectifiers), which adjust the input voltage of the motor by controlling the conduction angle of the thyristors. During the starting process, the thyristors gradually turn on, reducing the input voltage of the motor, thereby reducing the starting current. When the motor reaches the rated speed, the soft starter automatically connects the motor directly to the power supply, bypassing the thyristors to reduce heat loss and extend the life of the equipment.

Starting Mode

Ramp Boost Start: Gradually increase the voltage by adjusting the conduction angle of the thyristor, suitable for occasions that require smooth starting.

‌Ramp Constant Current Start: Keep the current constant during the starting process, suitable for loads that require constant torque.

‌Step start‌: quickly reaches the set current at the beginning of the start, suitable for loads that need to start quickly.

‌Pulse impact start‌: at the beginning of the start, a large current is turned on for a period of time, then falls back, and then rises linearly according to the original set value, suitable for loads that require a large initial torque‌.

Application scenarios

Soft starters are widely used in various motor systems that require smooth start, especially in high inertia systems. It can reduce the impact current when the motor starts, protect the motor and the power grid, and improve the overall efficiency and safety of the system‌