3. Soft starter or frequency inverter?

In order to achieve a soft start in asynchronous motors / three-phase motors, a frequency inverter is often used. Here, the speed can be slowly increased to the full value using a programmable ramp function. In contrast to reducing the voltage with a soft starter, the motor has a high torque even at low speeds when operated with a frequency inverter. The speed can therefore also be increased very slowly, e.g. B. to cope with large moments of inertia. The torque can briefly have higher values than in nominal operation, so that starting under full load is also possible. This is important when starting, among other things, of compressors when they have to start against the pressure that is still present.
Another advantage of frequency inverters is the ability to vary the speed of the motor during operation and, depending on requirements, to slowly reduce the speed or brake the motor in a controlled manner when switching off. From a technical point of view, a frequency inverter is much better. If only a reduced starting current is required without load, a soft starter has an advantage for cost reasons alone.