The impact of using frequency converters on the performance curve of water pumps
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I encountered a case where the designed discharge capacity of the sewage pump was 20,000 cubic meters per day. Due to significant fluctuations in the water volume transferred from outside the water treatment station, an inverter was installed to control the flow rate. However, even after setting the frequency to 50 Hz after completion of the construction, the discharge volume was only 18,000 cubic meters per day, which is not sufficient to reach the pump’s rated discharge capacity. What impact does the use of an inverter have on the performance curve of a centrifugal pump? What’s the principle? Please ask the teacher for an explanation.
The impact of frequency converters on the performance curve of water pumps is mainly reflected in the following aspects: 1) Flow rate: The use of a frequency converter allows the flow rate of the water pump to be changed, thereby altering its performance curve. 2) Efficiency: The function of the frequency converter results in a significant improvement in the efficiency of the water pump, which in turn affects its performance curve. 3) Head: The frequency converter enables a significant increase in the head of the water pump, which also affects its performance curve. 4) Noise: Inverters can significantly reduce the noise generated by water pumps, which in turn affects the performance curve of these pumps to a certain extent. -
It has nothing to do with drive via an inverter; it’s a problem with pump selection – the head value chosen is too low
The issue with the actual speed of the motor is that there is a discrepancy between the frequency set by the inverter and the frequency generated by the motor; this results in a speed that is lower than that at the power frequency. Speed is proportional to flow rate, so as the speed decreases, the flow rate also decreases.
The flow-head characteristic curves of variable-frequency motor centrifugal pumps and conventional power-frequency motor centrifugal pumps are opposite to each other; that is, in the former, both flow rate and head decrease when the frequency and speed are reduced, while in the latter, the head increases as the flow rate decreases. Therefore, variable-frequency motor centrifugal pumps are not suitable for applications where a relatively stable pump outlet pressure is required while the flow rate can be adjusted, to avoid a too large drop in head at low flow rates that would prevent delivery of fluid.