When the electric drive of a motor does not determine a variation of the speed of the motor, requiring only a smoother start, in order to limit the starting current, avoiding power supply voltage drops, a great option consists of the use of soft-starters . Soft-starters are static starters designed to accelerate, decelerate and protect three-phase induction motors by controlling the voltage applied to the motor. Its use is common in centrifugal pumps, fans and motors of high power, whose application does not require the variation of speed.

These electronic devices are made of thyristor bridges (SCR or TRIAC) driven by a microcontroller electronic board. Thyristors are electronic components notably developed to work on alternating current. When SCR (silicon controlled rectifiers) are used, they are used in the antiparallel configuration, ensuring current flow in both directions, as with TRIAC skf bearing 6004 zjem. By way of comparison, a TRIAC can be visualized as two SCRs, arranged in antiparallel. The soft-starter controls the voltage across the motor through the power circuit, formed by the thyristors, varying the firing angle thereof and consequently varying the effective voltage applied to the motor.