The Soft-Starter is an electronic device made of antiparallel-shaped thyristor bridges (SCRs) driven by an electronic board to control the starting current of three-phase AC electric motors. Its use is common in centrifugal pumps, fans, and high power motors whose application does not require the variation of speed. The soft-stater controls the voltage across the motor through the medium of the power circuit, established by six SCRs, varying the firing angle thereof and, consequently, varying the effective voltage applied to the motor.

In this way we can control the starting current of the motor, guaranteeing a “soft start” in a way that does not cause abrupt electrical voltage drops in the mains, as in direct starters. At the end of the starting period, adjustable, usually between 2 and 30 seconds, the voltage will reach its full value after a smooth acceleration or an ascending ramp. They usually work with the technology called by-pass, that after the electric motor starts and receives all the voltage of the network will be connected to a contactor that replaces the modules of thyristors, avoiding their overheating. https://www.mrosupply.com/bearings/spherical-roller-bearings/321803_22222-ec3_skf-bearing/