Soft starter for 3-phase motors, S3-400-3.0-7.5

Asynchronous motors are often started directly or with a star-delta circuit. During direct start, extremely high starting currents occur, ranging from up to seven times the motor's rated current. The star-delta circuit mitigates the problem by providing a root-three lower phase voltage. However, switching from star to delta also creates a significant current spike. These starting methods can overload the network, disturb other consumers, cause mechanical problems, and expose the entire drive to high wear and tear.

The solution to these problems is a soft starter. During startup, the starter reduces the voltage in two of the three phases through phase-cut control. Throughout the adjustable starting time, the torque slowly increases until the full mains voltage is applied to the motor. This results in a network- and drive-friendly, smooth acceleration of your drive. Extremely robust, anti-parallel connected thyristor pairs are used as switching elements.

The adjustable potentiometers determine the acceleration time and the starting torque.

With the jumper, you can activate the kickstart (only S1 and S2) when a high breaking torque is needed. Once the motor has accelerated, the control switches the integrated bypass relays, ensuring that no loss heat occurs during operation.

In soft starters with current control, the user simply sets the desired current and thus the starting torque. The acceleration time of the drive is then automatically determined by the load conditions. If the current is insufficient for a startup, the starter will terminate the process after 30 seconds to prevent overheating.

Please note that at lower voltages, the torque of the asynchronous motor decreases quadratically. Therefore, a soft starter is not suitable for hard-starting drives. For this application, it is better to use a frequency inverter as a starter, which we are also happy to offer you.