Soft starters and variable frequency drives (VFD) can both be used to reduce the inrush current and torque that can occur when motors are accelerated to full speed, and both protect motors from damage at startup. There is a key difference, however, in that VFDs control motor speed throughout the run cycle and soft starters are only used during startup and stop. Choosing between the two depends on the application, performance requirements, and overall costs.
Soft starters, also known as reduced voltage soft starters (RVSS), work by gradually ramping up voltage to the motor. They are often used in applications such as cooling towers, large circulation pumps, and fans that only require speed and torque control at startup. Soft starters are smaller and less expensive than VFDs.
VFDs, unlike soft starters, offer constant speed control during the entire operating cycle of a motor. They range from basic to full-bypass, which allows uninterrupted equipment operation in the event of VFD failure. VFDs offer superior energy savings, integration, control, and diagnostics. Though they can initially cost two or three times more than a soft starter, VFDs are often a better overall value for applications that require the energy and functionality advantages they offer. Omni can help clients determine whether a VFD should be used for their particular application, or if a soft starter will suffice.
Omni Instrumentation & Electrical Services, Inc. is a premier instrumentation and electrical contractor, providing superior total care solutions since 1986. Services include instrument installation, tubing installation, instrument calibration, control loop testing, startup and commissioning, power and lighting, process control wiring, BMS wiring, telecommunications and data wiring, fire alarm wiring, security wiring, process network wiring, and control panel fabrication. Omni Instrumentation & Electrical Services, Inc., is certified in Foundation Fieldbus, Profibus, DeviceNet and ASI-Bus installation.