Hello, we are currently experiencing vibration issues with a high voltage electrical motor. Despite having the unit repaired two months ago, we have not seen any improvement in its performance. We are seeking assistance from individuals skilled in analyzing vibration spectra to help determine the root cause of the problem. Data has been collected from various positions using an accelerometer and portable data collector, measuring velocity (mm/s) with dominant frequencies of 1X, 2X, and 3X at different locations, along with lower amplitudes of 0.5X, 4X, 5X, 6X, etc. Interestingly, the vibration levels initially appear good for the first 10 minutes after startup but increase as the motor temperature rises. After conducting an analysis, we have identified a potential combination of two defects: mechanical looseness and misalignment. Can anyone else in this forum confirm this analysis? Thank you.
Could the coupling have worn out and need to be replaced during repairs? Various couplings can produce unique signatures of turning speed harmonics. It is likely that misalignment issues are caused by thermal expansion in either the motor or the driven equipment, as alignment seems stable during the initial ten minutes of operation. To address this, it may be necessary to assess the amount of thermal expansion present and adjust alignment accordingly. It might be necessary to intentionally misalign initially so that thermal expansion can bring the unit into proper alignment.
Inquiring about the condition of the coupling during repairs could provide insight into the varying signatures of turning speed harmonics. It is possible that misalignment issues are stemming from thermal expansion in either the motor or the driven equipment. Monitoring the alignment stability within the first ten minutes of operation can help identify potential issues. To address thermal expansion, it may be necessary to factor in and compensate for the amount of growth present during the alignment process. Starting with a slight misalignment can allow for the thermal growth to naturally align the unit.
The motor was reinstated without replacing the coupling, so we will proceed as planned. Your insight on thermal growth is correct, and we will be requesting an alignment check once more. Additionally, I will provide you with spectra frequencies to show the vibration signatures at various measurement points. In NDE H, the dominant frequency is 2X (1.53 mm/s) with the presence of 0.5X (0.54 mm/s), 3X (0.54 mm/s), and very low amplitudes of 5X and sideband frequencies between 2 kHz and 2.5 kHz. NDE V shows a dominant 1X frequency (4.55 mm/s) with low amplitudes of 2X and 3X, along with sideband frequency components between 2 kHz and 2.5 kHz. In the axial NDE, the dominant frequency is 3X (0.87 mm/s) with the presence of 0.5X (0.45 mm/s) and 2X (0.74 mm/s), as well as low amplitudes of 1X, 3X, and 4X, and sideband frequency components between 2 kHz and 2.5 kHz. DE H displays a dominant 2X frequency (1.72 mm/s) with the presence of 0.5X (0.33 mm/s), 1X (0.59 mm/s), and low amplitudes of 3X, 4X, and 7X. DE V exhibits a dominant 1X frequency (3.39 mm/s) with a relatively high amplitude of 3X (2.20 mm/s), along with low amplitudes of 2X, 4X, and sideband frequency components up to 500 Hz. Axial DE shows a sideband frequency component up to 500 Hz, with a dominant 3X frequency (7.10 mm/s) and the presence of 1X (2.17 mm/s). Your expertise would be greatly appreciated.
It sounds like you're on the right track with your analysis, especially considering the symptoms change as the motor heats up. Mechanical looseness often shows up in the form of harmonics like 2X and 3X, while misalignment can definitely contribute to those lower order vibrations. Have you checked the mounting and the alignment of the motor to the driven load? It might also be worth investigating if thermal expansion is affecting the alignment as the motor gets hot. Good luck, and let us know what you find out!
It definitely sounds like you’re on the right track with your analysis. The symptoms you’re describing—particularly the increase in vibration with temperature—can often indicate thermal expansion issues exacerbating existing misalignment or looseness. It might be worthwhile to check the mounting points and any associated couplings for tightness, especially since you've noted the vibration levels seem acceptable at first. Have you also considered inspecting the bearings? They can contribute to similar vibration patterns if they're wearing unevenly or if there's any lubrication issue. Keep us updated on what you find!
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Answer: - Common causes of vibration issues in high voltage induction motors can include mechanical looseness, misalignment, unbalance, bearing defects, electrical problems, and resonance.
Answer: - Vibration spectra analysis involves measuring vibrations at various frequencies to identify patterns that indicate specific problems like unbalance, misalignment, or bearing defects. This analysis can help pinpoint the root cause of motor vibration issues.
Answer: - The increase in vibration levels as the motor temperature rises could be due to thermal expansion causing changes in the mechanical properties of the motor components, leading to issues like misalignment becoming more pronounced.
Answer: - The potential combination of mechanical looseness and misalignment has been identified as the root cause of the vibration issues in the high voltage induction motor. These defects can lead to increased vibrations and reduced performance.
Answer: - To confirm the analysis of mechanical looseness and misalignment in the motor, additional diagnostic tests such as laser alignment, vibration analysis at different operating conditions, and inspection of the motor components may be required to validate the findings.
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