Issues with parallel operation of variable-frequency pumps
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Assume that the current demand is 300 t/h at a head of 20 M; two pumps with a capacity of 150 t/h and a head of 20 M are used. The pump is a variable-frequency pump. At this point, if the operational requirement increases to 100 t/h, and a pump with a capacity of 150 t/h is used with its speed adjusted to 100 t/h, the pump’s head will be greater than the resistance in the piping. For example, the pump head is approximately 10 M based on the ratio, and the pipeline flow resistance is only 4 M. Could there be any problems with this way of operating? The system is not equipped with a control valve.
The frequency of the variable-frequency pump can be adjusted freely, providing a more intuitive view of the current.
The operating point of the pump is determined by the pump’s performance curve and the plant’s characteristic curve
There are two modes for your operation: one is manual frequency tuning, which is a mode that limits traffic. One is the automatic mode that sets a constant voltage. Since the pipe resistance is only 4 meters, manual frequency tuning can effectively regulate the flow rate. If pressure is used for setting, overflow operation is very likely to occur.
This post was last edited by 3983596_FPPZ on 2019-4-22 07:41. The flow rate changes from 300 to 100, and the head changes from 20 to 10; this represents a variation within a certain parameter range. As long as the extreme values meet the requirements, variable frequency control will enable the system to meet the parameters at any point within that range, with the values always being sufficient and never insufficient
The operating point of the pump is determined by the pump’s performance curve and the plant’s characteristic curve
The adjustment of variable-frequency centrifugal pumps requires comprehensive consideration of factors such as pipeline resistance, back pressure, frequency variation range, and control method. Regarding the situation described by the original poster, it is likely difficult to achieve this without back pressure and manual control. It is possible if back pressure is taken into account. Of course, manual control is also an option. Speaking of pumps alone, as long as they are within the variable frequency flow-rate and head range, they will work fine.
Designing a system for 300 but only transporting 100 is no problem at all; it’s something you can do casually.
I understand there should be no problem; I agree with the opinions from the 4th and 7th floors. It should be possible to achieve this by combining the adjustment of the pipeline network resistance via the pump outlet valve with frequency conversion control.