Reasons for high current in centrifugal pump motors
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Help: There are two single-stage, single-suction centrifugal pumps, with a rated current of 220A each. The motor currents of both pumps, A and B, were normal initially – 165A for pump A and 160A for pump B. The medium transported by these pumps is PX. Starting from October 29th, the motor currents of both pumps began to rise gradually, reaching 193A. Upon inspection of pump A, everything appeared normal; the clearance at the seal ring was also within the normal range (0.50 mm on one side). After cleaning the impeller, the current during testing was 177A, and this value remained stable. Check Station B and replace it with an impeller from the original manufacturer; the current is 179 A, and it remains stable. Why hasn’t anything else been replaced, yet the current is higher than before? There is a flow control valve at the outlet, and the flow rate doesn’t change before or after maintenance – so why is the current still higher than before? Please help to figure this out
It may be related to shaft alignment or the elastic blocks.
Alignment is done by using a dial, so there’s no problem
Are there any problems with the motor bearings? Are the specific gravity and temperature of the medium the same as before? What is the insulation level of the motor?
There is no problem with the motor bearings; the motor was also tested under no-load conditions, with a no-load current of 59A. The specific gravity, temperature, and viscosity of the medium remained unchanged. Thank you.
Reasons for high current: 1. Increased flow rate； 2. As the temperature drops, the density of PX increases, resulting in an increased output power of the motor.
Due to the large change in flow rate, there is no margin in the flow rate of the selected pump. After use for a period of time, issues such as resistance at the inlets and outlets, pipeline impurities, medium viscosity, and mismatches between head and flow rate arise. Then there are mechanical problems, such as wear and tear of components and bearings. In short, it is the increased resistance that causes the current to become too high. The flow rate can be reduced by closing valves, or, while still meeting the process requirements, both the flow rate and head can be decreased (the flow rate can be controlled using a flow meter to meet the process requirements), thereby preventing the motor from being overloaded.
The influence of medium viscosity, density, temperature, and so on on conveying performance
The analysis is mainly based on the following reasons: 1. Medium-related factors – whether there have been any changes; since both pumps increased in pressure at the same time, equipment-related issues can be basically ruled out； Analyze to determine whether the increase in shaft power is caused by changes in the medium ； 2. For the mechanical components, conduct a thorough inspection; as mentioned in point 1, this possibility is very low. 3. Check the impeller to see if scaling or an uneven surface on it is causing increased operating resistance ； 4. Check the opening degree of the outlet valve. I’m not sure if the outlet flow control is handled by the same valve; verify whether there are any deviations in the flow readings ； 5. Check the inlet and outlet pipelines. 6. Other reasons – it’s difficult to determine. This situation is indeed difficult to explain, as no abnormalities can be detected in the device itself; therefore, it’s necessary to approach the issue from various angles and rule out possibilities one by one. Handle it patiently; don’t be afraid of the hassle – a reason will always be found
The pump’s rated flow rate is 102 m3/h, with a head of 202 meters. The flow rate of the outlet control valve is 58.2 tons per hour; the specific gravity of PX is 0.86, which results in a flow rate of 68 m3/h. Therefore, there is no issue of excessive flow. Thank you.
I understand it the same way; perhaps the viscosity of PX has changed. Our company has an analysis lab, but viscosity analysis was not part of the services offered there before.