Difficult case: Abnormally high current in the centrifugal pump.
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Overview: The company has a centrifugal pump used for transporting heavy diesel fuel. Its designed power output is 200 KW, the supply voltage is 10,000 V, the normal operating current is 15 A, and the pump’s rated flow rate is 280 m3. After operating for a period of time, at a constant flow rate, the current will rise gradually until it causes tripping due to overcurrent protection. In the figure below, the upper line represents the trend of the medium flow rate, while the lower line shows the trend of the current. It is clear that the flow rate remains stable, but the current keeps increasing. We checked the following: 1. No problems were found with the electrical wiring and distribution panels. 2. The motor was sent outside the factory for testing, and no problems were found; a motor taken from another location was installed in its place, but the current level still increased. 3. The pump body was disassembled for inspection; no problems were found with the mechanical seal or impeller. 4. The filter screen was removed, and there was no blockage. 5. The pump’s outlet pipeline is single, and the flow rate is stable; no leakage of the fluid was detected. 6. The pump operates without any abnormal vibrations, and there is no unusual heating in any part of it. After carrying out these inspections, the problem still persists, and I really don’t know what to do. I would appreciate it if experts could advise me on how to resolve this issue. Additional information (2025-3-25 10:05): An update on the progress – recently we disassembled the pump again, and upon inspection, it was found that: 1. The two impellers had varying degrees of thinning due to cavitation erosion ； 2、There is a corrosion-induced perforation on the drive side of the volute (volute chamber short circuit). We believe that cavitation is the direct cause of corrosion, but the reasons behind the occurrence of cavitation are not yet clear.
After ruling out problems with the motor and the pump itself, it is recommended to focus on the following aspects: 1. **Changes in the properties of the medium**: Check whether there are any changes in the viscosity, density, or impurity content of the heavy diesel being transported. Even minor changes in physical properties can lead to an increase in pump load, thereby affecting the current. 2. **Compatibility between pump and piping system**: Ensure that the operating point of the pump matches the system’s characteristic curve. A mismatch may cause the pump to operate at a non-optimal efficiency point, thereby consuming more electricity. 3. **Lubrication system inspection**: Check whether the bearings of the pump and its lubrication system are functioning properly. Interference or inadequate lubrication can increase friction, leading to an increase in current consumption. 4. **Power supply issues**: Although you have already checked the electrical wiring and distribution cabinets, it is still possible to further verify whether the power voltage is stable; voltage fluctuations or imbalances can also affect the motor current. 5. **Effect of thermal expansion**: Check whether, after the pump has been operating for a period of time, thermal expansion causes the internal gaps to decrease, thereby increasing operational resistance. 6. **Control system failure**: Verify whether the pump’s control system (such as frequency converters, starters) is operating properly. Incorrect signals or settings may cause abnormal current flow. Through the above checks and adjustments, it should be possible to get closer to the root causes of this complex problem of solving agricultural issues. At the same time, it is recommended to record detailed operational data to enable more thorough trend analysis. .
1. Check the gap of the mouth ring: are there any signs of abrasion, and has there been any backflow? 2. With the flow rate remaining unchanged, has the head changed? 3. Has there been any change in the medium components, and has the density increased?
Thank you for your reply. Regarding your question, the following additional information is provided: 1. No abnormalities were found in the gap of the mouth ring. 2. The pump outlet pressure remains stable during current changes. 3. The medium is relatively stable, with almost no change in density.
Check whether the process water cooler before the pump and the seal flushing water cooler are leaking, as water may be entering the diesel
Are there any adhered deposits on the impeller?
Be sure to study it carefully*; it’s such a great example