A Universal Controller for Parallel Pumps with Variable-Frequency Drives

There is an established trend to install variable-frequency drives in pumping applications. The object is to obtain continuously variable flow with high efficiency, while retaining the ability to bypass the drive via direct line operation of the ac induction motor. The system specifications often include parallel banks of pumps; with elaborate requirements for sequential staging in response to demand, alternation to equalize wear, and automatic accommodation of component failures. A universal controller is described that has been developed for such applications. Operating experience is summarized on more than 50 installations over the past three years.