What Is A Soft Starter?

What is a soft starter?

Soft starter:
Soft starter is an advanced motor control device that integrates motor soft start, soft stop, light load energy saving and multiple protection functions.
The soft starter makes the motor input voltage gradually increase from zero according to a preset function relationship until the start result, giving the motor full voltage, which is soft start. During the soft start process, the motor starting torque gradually increases and the speed gradually increases.
When the motor reaches the rated speed, the soft starter will intelligently replace the thyristor with a bypass contactor to provide a stable rated voltage for the motor, which not only reduces the heat loss of the thyristor, prolongs the service life of the soft starter, but also improves its working efficiency, while reducing harmonic pollution to the power grid. In addition, the soft starter also provides a soft stop function, which is the opposite of the soft start process. By gradually reducing the voltage, the number of revolutions is steadily reduced to zero, effectively avoiding the torque shock caused by free stop.

The role of the soft starter:
Overload, phase loss, overheating protection function, measurement circuit parameter function, etc.

Starting methods of soft starters:
Ramp boost soft start: This is the simplest starting method. By adjusting the conduction angle of the thyristor, the voltage gradually increases over time. Although the operation is simple, due to the lack of current limiting, it may cause a large impact current, which has a great impact on the power grid and equipment, so it is rarely used in practice.
Ramp constant current soft start: At the beginning of the start, the current gradually increases, and after reaching the preset value, it remains constant until the start is completed. This method is widely used in the start of fan and pump loads, which can effectively reduce the impact current at start and protect the equipment.
Step start: When starting, the starting current quickly reaches the set value. By adjusting the preset value of the starting current, an efficient starting effect can be achieved. This method is particularly suitable for occasions with strict requirements on the start time.
Pulse impact start: At the beginning of the start, the thyristor conducts with a large current for a period of time and then falls back, then rises linearly according to the original set value, and finally connects to the constant current start. This method is suitable for occasions where large static friction needs to be overcome, but it is less used in general loads.
Voltage dual ramp starting: During the starting process, the motor output torque increases with the voltage, providing the initial starting voltage. When the motor reaches the rated speed, the output voltage reaches the rated voltage. This method can effectively reduce the impact current during starting.
Current limiting starting: During the starting process, the current is limited to a certain set value to ensure the safety of the motor and the power grid. This method is suitable for occasions with strict requirements on the starting current.

Classification of soft starters:
AC motor
DC motor
Special motor