Questions about centrifugal pumps
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This post was last edited by wawa*n*ntaozi on 2016-5-14 at 11:39. Our circulating water pump model is 200S-42A, with a flow rate of 270 liters/h and a head of 35 meters； Shaft power: 37KW Efficiency: 80% NPSHR: 6m; speed: 2900rpm. During operation, the operating current of the two pumps (of the same model) remains at around 88% of the overload protection limit, which is quite high. Some time ago, both devices suddenly triggered their overload protection and shut down at the same time ； Later, a no-load test was conducted on the motor; the operating current was around 20% of the overload protection level, which is within the normal range ； The water pump also has its pump casing open; there are no debris inside the pump, and the pump shaft is not tangled. After that, the circulation tank was cleaned, and it was found that the pump inlet filter screen was clogged with flocs, and the inlet flexible connection had been flattened. Here’s the question: The motor is working fine, and the water pump is also functioning properly (the packing is a bit tight, but there have been no issues with its operation). Yet both pumps suddenly switched off due to overload protection. Could this be related to an obstruction at the inlet? A blocked inlet can lead to cavitation, causing pressure fluctuations; as a result, the current levels will also fluctuate. Could it be that the peak value of these current fluctuations exceeds the protection current level, thereby triggering a shutdown? Friends at sea, let’s discuss this! ! (After replacing the imported filter, the water pump is running again; the current level remains above 80%, but it continues to operate normally.) My boss asked me to analyze the reasons for jumping out of the car; I’m not sure if this explanation holds water I forgot to add the most, most important thing! ! ! The two circulating water pumps were upgraded in February this year; the outlet pipelines were changed from DN150 (with the pump outlet being DN125 and then enlarged to DN150) to DN200 (with the outlet being DN125 and then enlarged to DN200) ； The combined outlet manifold for the two pumps has been changed from DN200 to DN350; this was done because the total amount of circulating water was not sufficient. After this change, the pumps operated in a region with high current levels (this is related to the change in the outlet pipelines). Could it be that the change in the outlet pipelines altered the characteristics of the piping system, thereby changing the operating point of the pumps? In other words, the flow rate increased, and the operating point of the pumps shifted to the right side of the performance curve, resulting in an increase in power consumption as well? ? ? ? ?
Axial power 37KW? What is the motor power? Is traffic monitored?
Axial power 37KW? What is the motor power? Is traffic monitored?
Measure the outlet head and compare it with the performance curve provided by the pump manufacturer; check whether the flow rate and power values on that curve exceed the limits
I agree with your analysis; I think the culprit is also the inlet filter – its blockage leads to too low an inlet pressure, and the pump may suffer from cavitation (I’m not sure if the impeller was inspected when the pump was taken apart). Is 37kW the pump shaft power or the motor power? Also, what is your overload current? This can be used to determine whether the normal current value is within the acceptable range.
I agree with your analysis; I think the culprit is also the inlet filter – its blockage leads to too low an inlet pressure, and the pump may suffer from cavitation (I’m not sure if the impeller was inspected when the pump was taken apart). Is 37kW the pump shaft power or the motor power? Also, what is your overload current? This can be used to determine whether the normal current value is within the acceptable range.
First, you need to determine whether it was an overload-induced jump out. In the case of a clogged filter, overload trip usually does not occur; only underload trip happens. Also, if the filter is severely clogged, there should already be problems with flow rate. It is recommended to check whether there is an underload setting in the electrical system!
Let’s check whether the outlet flow exceeds the design value. Some of our pumps have outlet valves that cannot be opened too wide, otherwise there will be an electric current overload that causes the system to shut down; therefore, the outlet valves are used to limit the flow.