Correct choice of motor power (are water transport considered? )
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The density of the pumped medium is now small, and the motor requires self-starting. When calculating the motor power, consider the maximum flow rate and medium density to select an appropriate motor power. However, considering the on-site water test (the workshop test requires the manufacturer to select a large motor in stock), the motor power is calculated based on the water density and minimum flow rate. This power may be much greater than the power selected previously. In this case, how to choose the correct motor power? Just give an example: The medium density is 445kg/m3, the minimum/normal/rated flow rate is 450/560/620m3/h, the head is 150m, and the pump efficiency is 75%. Based on the medium density and rated flow rate, the motor shaft power is calculated to be 150.3kW. Considering the end of the curve and the motor margin, 185kW is selected. Considering water transportation at this time, the motor shaft power calculated based on water density and minimum flow rate is 245.1kW. At this time, at least a 250kW motor must be selected. Comparing the two, should the distribution motor of this pump be 250kW or 185kW? The power gap between the two is not small.
Prerequisites: The company's funds are relatively tight, there are backup pumps, and management is standardized. In this case, I suggest you choose a low-power motor and run the backup pump at the same time during water transportation. This can generally ensure that the minimum flow requirements are met without exceeding the rated power of the motor. If the prerequisites are not met and it is a necessary procedure before the device is put into use and after overhaul during water transportation, then a large motor should be equipped, and it should be greater than 250KW.