What causes the current of a centrifugal pump to increase gradually?
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It is a 380V single-stage horizontal centrifugal pump, used for handling steam condensate. The current level is around 108 when the pump starts up; thereafter, this current gradually increases, by about 1A per day. Once it reaches 135, the pump must be shut down, otherwise a circuit breaker will trip. The current level in the backup pump also rises gradually from 108, and once that pump is switched in, the current still increases slowly from 108. The pump outlet pressure remains essentially constant, and the process parameters have not changed. The motor was checked and found to be fine; the same was true after replacing it. The pump was disassembled, and no problems were found. It’s a strange question – have any experts encountered this phenomenon?
It’s better to check the outlet valve to see if it is gradually opening due to vibration. You might try securing the valve’s packing or fixing the valve’s opening limit as a solution; just for reference :)
Check the outlet valve and pipelines; it’s also possible that the outlet is a heat exchanger, and that heat exchanger is scaled.
The outlet valve is fully open; there are three users at the outlet, each equipped with a flow meter and a control valve. There is no backflow from this pump, so an increase in flow rate is not possible – it must be due to some other reason. Abrasion is also basically ruled out, as the vibrations are excellent; it’s a very strange phenomenon.
There is no heat exchanger at the outlet; the three users are regulated by control valves, and each is equipped with a flow meter.
A water supply system cannot be considered to have no flow issues just because the outlet valve is fully open. Problems with the main return valve can also lead to an increase in flow rate; it would be best to provide a schematic diagram of the water system, as this will make things clearer when examining the diagram. For reference.
Each user has a control valve and a flow meter
Does the current increase while the pump outlet pressure remains unchanged? As the current increases, the flow rate should also increase, and the outlet pressure of the pump should decrease, right? Isn’t it?
With constant pressure, the current is not solely related to flow rate; it reflects only the amount of work done. Flow rate represents part of the useful work, while there is also unnecessary work. It seems that it is the components of this unnecessary work that are changing, though it’s not clear yet what they are.
Since the failure symptoms are the same for both pumps, it indicates that the cause is not related to the pumps themselves, but rather lies in the common parts at the inlet and outlet. Check whether the inlet pressure and operating voltage of the pump are changing normally
Pay close attention to the level, pressure, and temperature parameters of the condensate tank, and check the recording curves in the control system