Choosing between a soft starter and a VFD to fit your application
By K Danielson, Eaton
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Electricity+Control, July 2013 (pages 4 – 6)
Soft starters are used in applications where:
- Speed and torque control are required only during start-up (and stop if equipped with soft stop)
- Reducing large start-up inrush currents associated with a large motor is required
- The mechanical system requires a gentle start to relieve torque spikes and tension associatedwith normal start-up (for example, conveyors, belt-driven systems, gears, etc)
- Pumps are used to eliminate pressure surges caused in piping systems when fluid changes direction rapidly
Variable frequency drives (VFDs) are used in applications where:
- Complete speed control is required
- Energy savings is a goal
- Custom control is needed
- The choice of either a soft starter or a VSD depends on the application.
- A VSD has the benefit of being able to ensure more efficient motor operation.
- Lifecycle costing, including energy usage, must be factored into the decision as to which is the best choice.