Continued from the article: Benefits of variable frequency drives (VFDs, frequency inverters) (...
1. A variable frequency drive (VFD) may be used for control of process temperature, pressure or flow. This application of VFD (VSD) is without the use of a separate controller. Suitable sensors and electronics are used to interface the driven equipment with the variable frequency drive (VFD, frequency inverter).
2. Maintenance costs of the controlled system can be lower, since lower operating speeds result in longer life for bearings and motors.
3. Eliminating the throttling valves and dampers also does away with maintaining these devices and all other associated controls.
4. With variable frequency drive (VFD), the soft starter for the motor is no longer required.
5. Controlled ramp-up speed in a liquid system can eliminate water hammer problems.
6. The ability of a variable frequency drive (VFD, frequency inverter) to limit torque to a user-selected level can protect driven equipment that cannot tolerate excessive torque.
In a liquid system VFDs are absolutely great. Especially in a multi-tier cascade where accuracy is vital. The best type is a programmable curve VFD at the operator station for those situations when you truly need to adjust on the fly. The last plant I had the pleasure to work with these consisted of about %90 VFD on all control systems. Was very nice and the consistency is unmatched.