After starting up on July 27, 2024, significant fluctuations in vibration trends were detected on bearings # 6 and 7 of the Turbine/Generator, along with minor fluctuations on bearings # 1, 4, and 5, using the ALSTOM Transient Data Manager/ Turbine Diagnostic System (TDM). These fluctuations were observed on the X and Y Relative probes of the TDM system, but not on the Vibro VM600 TSI system in the main control room. The vibrations were present even at zero speed and during turning gear operation at 2~3 rpm. Major fluctuations with amplitudes between 150 µm to 240 µm were noted at regular intervals on bearings # 6 and 7, with exceptions of no or minor fluctuations during night hours. Minor vibrations between 10µm to 20 µm were also observed on bearings # 1, 4, and 5. The vibration frequency of peaks at bearings # 6 and 7, measured by the X and Y probes, ranged from 270Hz (5.4x) to 570Hz (11.4x), with side bands visible in the waterfall plots. It is crucial to diagnose the fault based on this data, as the fluctuations are only apparent on the diagnostic system and not on the TSI system.
If you are experiencing fluctuations at zero RPM, it may not be true vibration. It is recommended to verify the integrity of the sensors and check for any nearby sources of noise that could be causing the issue. Make sure to investigate and address any potential factors that may be influencing the fluctuations. Subject: Analysis of Vibration Trends and Peaks on 340 MWe Steam Turbine Bearings# 6 and 7 at ALSTOM TDM System Observing substantial fluctuations in vibration trends at Bearings # 6 and 7, and minor variations at Bearings # 1, 4 & 5 on the ALSTOM Transient Data Manager (TDM) System post-startup on 27th July, 2024. These fluctuations are specifically seen on X & Y relative probes of the TDM system. Interestingly, these erratic vibrations are also present at zero speed and during the operation of the turning gear at 2~3 RPM. The significant fluctuations on Bearings # 6 and 7 exhibit amplitudes ranging between 150 µm to 240 µm at regular intervals, with occasional exceptions during night hours where minimal to no fluctuations are detected. Similarly, minor fluctuations between 10µm to 20 µm can be seen on Bearings # 1, 4, and 5. The vibration frequency at Bearings # 6 and 7 ranges from 270Hz (5.4x) to 570Hz (11.4x) on both X & Y probes, with side bands visible in the waterfall plots. It is crucial to analyze all available data to pinpoint the root cause of these fluctuations, as they are solely visible on the diagnostic system and not on the TSI system. Your attention to this matter is highly appreciated. Best regards, Muhammad Musa
When analyzing fluctuations in vibration trends, spectrum, and orbit plots on 340 MWe Steam Turbine Bearings #6 and #7 in the ALSTOM Transient Data Manager (TDM) System, it is crucial to consider the possibility of noise interfering with the signal. Issues can arise from the instrument loop or the target area on the shaft, so it is essential to investigate if there is a correlation between changes in vibration and other parameters like the axial position of the shaft. To further diagnose the issue, additional plots at 0 rpm and 3 rpm (slow roll) can provide valuable insights. One practical test to consider is swapping the cables of the vibration probes at the back of the rack to observe any effects. However, it is essential to conduct a risk analysis and adhere to facility policies before making any changes. Regards- Ali M Al-Shurafa.
Dear Ali Al-Shurafa, I would greatly appreciate it if you could share a filtered orbit with a 1x filter and let me know which software you used for the analysis. Thanks, Ahmad Kidwai Original Message: Hi, can you please share a 1x filtered orbit? What software did you use for the analysis? Thanks, Ahmad Ahmad Kidwai
When experiencing fluctuations in vibration trends, spectrum, and orbit plots on a 340 MWe steam turbine's bearings #6 and #7 at ALSTOM's Transient Data Manager (TDM) System, it is important to address potential grounding errors. False vibration instrument readings are often caused by electrical currents induced in the system. To troubleshoot this issue, ensure that proximeters are properly grounded according to OEM guidelines. Check the junction box's main grounding wire for tight adherence and absence of oil or varnish at connections. Additionally, inspect the main grounding element going into the ground for any voltage buildup. Technicians should perform a voltage check on the junction box metal and Copper ground element at the earthing level, ensuring that the voltage does not exceed 0.01 Volts. It is also crucial to consider AC wiring induced currents by separating vibration wiring from AC conducting wires in cable trays, following instrumentation standards for proper separation distances. Lastly, investigate rotor-induced electrical currents, such as electrical shaft currents in the turbine rotor or high rotor magnetism above 5 Gauss in the shaft or casing. By conducting these checks, you can identify and address any underlying issues affecting vibration trends on the turbine bearings. For further analysis and recommendations on diagnosing the fault based on available data, reach out with your findings. Remember to consult with experts for accurate troubleshooting and maintenance strategies.
Hello, I hope you are all having a great day. I wanted to share some valuable insights based on the previously posted recommendations. When experiencing fluctuations in vibration data, it is important to consider potential external sources such as noise or shaft voltage. One common issue that can contribute to these fluctuations is the lack of proper shaft grounding brushes. Additionally, damaged signal cable wiring from the Vibration data collector rack to the field device proximitor and the extension lead to the probe can also be sources of the problem. To troubleshoot this issue, conducting a megger test on the cable from the Rack to proximitor (with proximitor disconnected) can help determine if the cable is healthy or damaged. It is also recommended to check the extension probe lead and replace any old type proximitors that may be causing issues. It is important to ensure proper grounding of proximiters and check for any electrical currents induced by AC wiring or rotor magnetism in the turbine rotor. By addressing these potential sources of error and conducting thorough checks, we can pinpoint and resolve the fluctuations in vibration trends observed on the Turbine Bearings. Your attention to these details will contribute to the efficiency and reliability of the system. Thank you for your dedication and commitment to maintaining optimal performance. Best regards, Raffie Musaib-ali.
Given the data you provided, it indeed seems like there are some significant bearings issues going on, specifically bearings #6 and #7. The fluctuation rates at zero speed and during low RPMs indicate that there might be a misalignment or a deflection issue. The night-time reduction could just be due to non-operational or cooling down periods. It's also a bit concerning that these findings are only showing up on the TDM system and not on the VM600 - which either means there could be a sensing issue with the TSI system or the vibrations are too fine to be picked up, which further underlines the initial dysfunction you're dealing with.
Based on your data, these vibrations on bearings #6 and #7, particularly at zero speed, suggest imbalance or a possible misalignment issue. The fact that you're not seeing these results on the TSI system could be due to a difference in sensitivity between systems. It's also interesting to note the lack of significant fluctuations during nighttime hours. Could there be external influences causing these vibrations? I'd recommend checking aligning, conducting a physical inspection, and revisiting calibration of the TDM system, to make sure there's no instrument error. If the problem persists, you might need an in-depth vibration analysis done by a professional analyst.
It sounds like you have a complex situation on your hands with those vibration fluctuations! The fact that the significant spikes are only showing up in the ALSTOM system and not in the Vibro VM600 makes me wonder if there’s an issue with alignment or perhaps an external influence affecting those specific bearings. It’s worth investigating any changes in load conditions or environmental factors around the time the fluctuations were noted, especially given the patterns you've observed during different hours. Have you also considered running a more detailed analysis on the turning gear operation? Sometimes those low RPM conditions can reveal underlying issues that aren't as apparent at higher speeds.
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Answer: - The significant fluctuations in vibration trends on bearings 6 and 7 were detected after starting up on July 27, 2024. These fluctuations were observed on the X and Y Relative probes of the TDM system but not on the Vibro VM600 TSI system in the main control room.
Answer: - Major fluctuations with amplitudes between 150 µm to 240 µm were noted at regular intervals on bearings 6 and 7, with exceptions of no or minor fluctuations during night hours. The vibration frequency of peaks at bearings 6 and 7 ranged from 270Hz (5.4x) to 570Hz (11.4x), with side bands visible in the waterfall plots.
Answer: - Yes, minor vibrations between 10µm to 20 µm were also observed on bearings 1, 4, and 5.
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