Dancing With the Dragon
Efficiency of pump,motor and drive depends on various factors. Normally, the larger the output power of the pump, motor or drive, the higher the efficiency of the system. When the same system is operated at a low speed, the overall efficiency of the system also drops.
For a water pump designed to be operated in the 35 to 50 Hz range,the efficiency of the drive and motor system is about 90 percent at the rated operating point.
This drops to 83 percent at 35 Hz. The efficiency of the water pump itself varies between 50 and 85 percent. Generally speaking, the efficiency of pump is affected by its speed and system curve.
Just take a review on fundamental of Motor Pump
As illustrated by Table 1 , the relationship between the efficiency, power, rotation speed, flow rate and lift of a system can easily be determined.
In moving from working point A to B (upper diagram), the flow-rate is reduced by about 40 percent, on the
other hand, power is reduced by about 60 percent (lower diagram).