ABB's softstarter range steps from the compact PSR for basic in-line starting, through the PSE with voltage ramp and torque control, to the PSTX with full torque control, integrated bypass, fieldbus communication and pump-specific functions. All reduce starting current and the mechanical shock that damages couplings, gearboxes and pipework.
PSR for simple, low-cost starting of small motors. PSE where you want voltage ramp and torque control with built-in bypass. PSTX for large motors, frequent starting, pump control functions or fieldbus integration.
Not while running — once bypassed, the motor runs across the line. The savings are mechanical: less stress on belts, couplings, gearboxes and pipework, and lower peak demand charges from reduced starting current. For running energy savings you need a VFD.