Abnormal noise occurs when the fan operates at low speed
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The fan motor of the 25T boiler in our factory produces abnormal noises when operating at low speeds; it’s a regular-type noise, similar to that caused by small pits inside the bearing rings. It performs well at high speeds, with no abnormal noises. The fan is regulated using an inverter. The motor still makes abnormal noises at low speeds after having its bearings replaced. Operating the motor separately from the fan functions well at any speed, with no abnormal noises. Is there friction between the impeller inside the fan and the casing? However, the noise from the bearing at the fan end is significantly lower than that at the motor shaft extension end. If there is friction between the impeller inside the fan and the casing, the noise should be louder at the fan end. Are there any other reasons?
It’s possible that inside the bearing, if it’s not too large, applying grease will allow the grinding process to continue
Hey, how did you solve this problem? I’ve encountered a similar issue; could you share your solution? My email address is sunjieping@126.com. Thank you. The fan motor of the 25T boiler in our factory makes unusual noises when operating at low speeds – it’s a regular noise, as if there are small pits inside the bearing rings. It performs well at high speeds, with no abnormal noises. The fan is regulated using an inverter. The motor still makes abnormal noises at low speeds after having its bearings replaced. Operating the motor separately from the fan functions well at any speed, with no abnormal noises. Is there friction between the impeller inside the fan and the casing? However, the noise from the bearing at the fan end is significantly lower than that at the motor shaft extension end. If there is friction between the impeller inside the fan and the casing, the noise should be louder at the fan end. Are there any other reasons?
Even when the fan speed is very low, at just a few hundred revolutions per minute, it is not possible to detect any sounds indicating defects in the inner ring, outer ring, or balls of the bearings. Because this frequency is too high – there are more than 50, or even over 100, vibrations per second – human ears are unable to distinguish them. And if there are real defects, the sounds produced will combine together to create a relatively loud noise. To hear the intermittent impact sounds indicating defects in the inner ring, it is only possible when the fan speed is truly very low, such as during shutdown. OP, you might as well record the sound with your phone and then use software to slow it down in order to determine the frequency interval of the sound.
Let me describe the problem: I have an variable-frequency fan equipped with an ABB ACS800 inverter and a 315KW motor. At a low speed of 10HZ, there is obvious abnormal noise; once the speed reaches 20HZ, everything works normally. The vibration of the fan is also normal. I checked some information and found that it might be due to the carrier frequency of the inverter being too low. I consulted ABB engineers, who said that the ABB ACS800 inverter does not allow adjustment of the carrier frequency. I also suspect that it could be harmonic noise. Does anyone know how to resolve this issue?
I think it’s because, at the initial stage of designing the fan based on its parameters, the performance curve of the fan selected is relatively close to the surge region. When the fan starts operating, the system is relatively normal. After operating for some time, changes in the air volume, air pressure, and duct resistance within the system cause the fan to gradually approach the surge zone. This causes fan surge, resulting in intermittent abnormal noises. If the speed is increased, there is no sound; let’s see if that’s the case