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Soft-starters with onboard PLCs adapt torque to the load
At the recent SPS IPC Drives show in Germany, WEG unveiled a family of high-end soft-starters with built-in PLC functions that provide programmable control of induction motors. The soft-PLC allows the output torque to be adapted to the load, and start-up currents to be minimised.
The SSW900 soft-starters, which replace the earlier SSW07 series, expand WEG’s portfolio in an area that was previously not a focus for the company in Europe.
The starters cover output currents from 10–412A, 220–575V AC (three-phase) in four frame sizes. They support direct motor connections in wye or delta configurations, as well as wye/delta switching with six motor leads. This allows the three motor phases to be wired directly to the soft-starters’ three thyristor pairs. As a result, they need to provide only 58% of the rated motor current (corresponding to the phase current), allowing a smaller starter to be used for the same power level.
The soft-starters have built-in bypass contactors for long service lives, and minimal heat dissipation in switchgear cabinets. They support three different stop methods, as well as a kick-start function.
A real-time clock is built in, in addition to protection, diagnostic and status query functions. Commissioning and programming are assisted by “wizards”. A USB port allows the soft-start’s parameters and its soft-PLC to be programmed using free Windows software. The starters support Modbus RTU, Profibus DP, DeviceNet, Ethernet/IP, Modbus TCP and Profinet I/O communications.
