23 Jul 2024


Flexible soft-starts avoid torque peaks

The Brazilian motors and controls manufacturer WEG has developed a soft-start technology which, it claims, delivers an almost linear speed ramp during motor starting, avoiding the torque peaks that can produce abrupt accelerations with some loads. The technology, known as “totally flexible torque control” – or TFTC – uses similar vector and direct torque control concepts to those applied in WEG’s variable speed drives.

The technology is combined with the same 32-bit DSPs (digital signal processors) used in the drives, to ensure that the estimated torque remains close to the real torque developed by a motor during the entire starting process. This allows the torque curve developed by the motor to be matched to the torque curve required by the load. A constantly accelerating torque is possible, producing an almost linear speed ramp.

The TFTC technology allows users to select the type of torque control according to the type of load on the motor – for example, constant or quadratic loads, or loads with high or low initial torques.

WEG soft-starts

WEG has applied the TFTC technology in new range of soft-starts (shown above) that it says are suitable for almost any type of load that does not require the speed to be varied after starting. The 28 models in the SSW-06 range cover ratings from 22-475kW, with all models suitable for either 50Hz or 60Hz operation. There is a choice of 11 supply voltages from 220-575V (85-365A).

The six-lead starters can fit into the delta connection of existing installations. WEG says that they are up to 43% smaller than starters using standard connections with three leads. A by-pass contactor reduces the installation envelope and boosts energy savings.

Other built-in functions include: a kick-start function for heavy loads, and loads requiring high starting torques; a pump control function, to avoid water hammer; multi-motor starting capability; an electronic thermal relay and electronic motor protection; and a detachable, multi-language HMI, with a copy function that allows OEMs to copy parameters from one soft starter to another.