Variable frequency drives (VFD) offer a useful control option for the motors of many types of reciprocating and centrifugal equipment. For instance, VFDs can deal with centrifugal-pump suction recirculation problems; running at lower speed can help reduce damage and operating difficulties.
To understand how to apply VFDs effectively, you must know the characteristics of the system and the equipment. So, let’s look at a general procedure that can serve as a good starting point for evaluating specific cases — realizing, of course, that it can’t cover every possibility.
To evaluate a VFD application, we need the following:
- system information on pressure drop versus flow;
- pump performance curves for the existing impeller;
- pump performance curves for the maximum impeller; and
- pump inlet eye dimensions.