How to Calculate Motor Efficiency for Variable Speed Centrifugal Pumps
The calculation of the motor efficiency for a variable-speed centrifugal pump can be complicated and requires first the determination of the pump speed, efficiency, and brake horsepower (bhp) required by the pump at various points on the water system's flow head curve or in the system head area. Some pumping systems have just one pump while others can have as many as five or six pumps. To simplify this evaluation, we will consider single pump operation only.
Figure 11 describes a water system with a uniform system head curve while Figure 22 describes a system with a system head area. The system head area is caused by load shifting in the water system. This means that various water loads on the system are active at different times. Loads far from the pumping installation may be active at one time while water loads near the pump may be active at other times.