Vibration Analysis of Main Components Using Portable CMS in Wind Turbine Health Assessment

Why is there an increase in vibration amplitude in the gearbox? Possible Cause: Misalignment or imbalance in the gearbox due to wear in components like bearings or shafts.

Next Why: Why is there misalignment in the gearbox? Possible Cause: A failure or degradation in the bearing causing uneven load distribution across the gearbox components.

Next Why: Why did the bearing fail? Possible Cause: Insufficient lubrication or contamination of the lubricant.

Next Why: Why was the lubrication insufficient? Possible Cause: Lack of maintenance or improper lubricant quality.

Final Why: Why was the maintenance inadequate? Possible Cause: Inefficient monitoring or failure to use condition-based maintenance tools such as vibration analysis to detect early signs.

The production capacity of wind turbines is closely tied to their height and the size of their rotor, as wind speeds generally increase with altitude. Onshore turbines are subjected to various external forces, including high winds, seismic activity, thunderstorms, and earthquakes. This challenge is particularly notable in regions like China, the USA, India, Southern Europe, and East Asia.

In contrast, the surrounding environment significantly influences energy harvesting throughout the entire service life of wind turbines. This becomes especially challenging in demanding environments, such as coastal areas and open seas, as previews mentioned, where turbines contend with turbulent winds, shear forces, tower shadows, mass imbalances, aerodynamic challenges, wave impacts, wake effects, as well as hydrodynamic, gravitational, and geotechnical loads. These diverse factors leave a distinctive mark on the dynamic characteristics of the turbines. Thus, turbine dynamics is a complex, multi-directional, and multi-coupling phenomenon aggravated by external loads. These various loads collectively lead to significant vibrations in wind turbines, resulting in substantial deformations in amplitude. Turbulent airflow and vibration induced vortex, resulting from ground-level airflows, directly impact the stability of wind turbine blades and towers. These disturbances directly affect critical components like the nacelle and tower, propagating vibrations throughout the blades and drivetrain, producing operational noise, and contributing to fatigue. Understanding the structural dynamics of wind turbines is a crucial aspect of their design, incorporating technical and environmental considerations.

Vibration analysis in wind turbines is a critical tool for assessing the health of major components such as the gearbox, generator, and rotor blades. The integration of Portable Condition Monitoring Systems (CMS) provides an efficient, real-time, and non-invasive way to monitor and analyze vibrations from the turbine’s components. Early detection of abnormalities can prevent catastrophic failures, optimize maintenance schedules, and improve the overall reliability and operational efficiency of wind turbines.

Vibration Measurement Principles and Sensor Channels

Vibration analysis involves capturing signals from rotating machinery (wind turbine components) using accelerometers, velocity sensors, or displacement sensors. These sensors detect the vibration response of the components and transform it into measurable signals, typically in terms of displacement (mm), velocity (mm/s), or acceleration (m/s2).

• Accelerometers measure the rate of change of velocity, providing insights into the force exerted on mechanical parts. These channels are typically used to measure acceleration or shock-type vibrations, which are crucial for detecting impacts or irregularities in rotating machinery such as bearings and gears.
• Velocity sensors measure the change in velocity over time and are sensitive to higher-frequency vibrations. These channels monitor the vibration velocity, which is useful for detecting slower oscillations and is typically associated with faults in larger rotating components such as the rotor and gearbox.
• Displacement sensors measure the absolute movement of a component and are ideal for low-frequency vibrations, typically indicating misalignment or imbalance. These are used to measure the movement or displacement of specific components, such as rotor blades or shafts, to detect imbalance or misalignment.

?The vibration signals captured by these sensors are analyzed in both the time domain (direct waveform) and the frequency domain (spectrum analysis). The spectrum helps identify issues like imbalance, misalignment, gear defects, bearing faults, and resonance effects.

Techniques for Vibration Data Analysis

• Time Domain Analysis: This technique analyzes vibration signals directly from the time-series data. Features like peak-to-peak displacement, root mean square (RMS) value, or standard deviation are used to monitor trends over time. Abnormal spikes in time-domain data can signal sudden faults like bearing failure or catastrophic gear damage.
• Frequency Domain Analysis (FFT): In the frequency domain, vibration data is converted into a spectrum using Fast Fourier Transform (FFT). Peaks in the frequency spectrum represent the operating frequencies of the turbine's components. Harmonics or sidebands around these frequencies indicate fault signatures. Common fault frequencies include: Bearing fault frequencies: Indicating issues like spalling or wear. Gear mesh frequencies: Identifying wear, misalignment, or damage in gear teeth. Blade pass frequencies: Revealing aerodynamic imbalances or structural issues in rotor blades.
• Envelope Analysis: This technique is used to detect impacts or high-frequency events, which are typically associated with localized faults like bearing damage. By demodulating the high-frequency signal, this analysis provides better sensitivity to fault detection.
• Order Tracking: In rotating machinery like wind turbines, components rotate at variable speeds. Order tracking allows for the detection of specific frequencies in relation to the turbine’s rotational speed, making it possible to isolate fault frequencies despite varying operational conditions.

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Key Faults Detected by Vibration Analysis

• Imbalance: Vibration amplitude increases when mass distribution is uneven on the rotating components (e.g., rotor blades). Imbalance is typically identified by increased vibration in the low-frequency range (1x, 2x rotational frequency).
• Misalignment: Shaft misalignment results in increased vibration, particularly at multiples of the rotational frequency (2x, 3x, etc.). Misalignment causes uneven load distribution, contributing to early failure of bearings or shafts.
• Bearing Faults: Faults in bearings create characteristic fault frequencies, with certain patterns or harmonics indicating the type of defect (e.g., ball or roller bearing damage).
• Gearbox Issues: Faults in the gearbox manifest as harmonic peaks at specific gear mesh frequencies, with higher harmonics indicating wear or failure in the gear teeth.
• Blade Imbalance or Cracks: Rotor blade issues, including aerodynamic imbalance or structural cracks, create vibrations that are detectable at blade pass frequencies, which are multiples of the rotational frequency.

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Standards for Vibration Analysis in Wind Turbines

Vibration analysis in wind turbines follows several international standards that provide guidelines for measuring, analyzing, and interpreting vibration data. These standards ensure that the procedures are consistent, reliable, and accurate, and they help define acceptable vibration limits for the safe operation of wind turbines. Below are the key standards commonly followed in wind turbine vibration analysis:

1. ISO 10816: Mechanical Vibration – Evaluation of Machine Vibration by Measurements on Non-Rotating Parts

2. ISO 2954: Mechanical Vibration – Guidelines for the Measurement and Evaluation of the Vibration of Large Machines

3. IEC 61400-25: Communication for Monitoring and Control of Wind Power Plants

4. ISO 9001: Quality Management Systems – Requirements

• Wind turbine operators and maintenance teams follow ISO 9001 to ensure that vibration analysis processes, among other maintenance activities, are carried out with high consistency and quality.

5. ISO 1816: Mechanical Vibration – Measurement of Vibration in Turbomachinery (Gearbox and Turbines – Drivetrain and Generator)

6. IEC 61400-11: Wind Turbine – Acoustic Noise Measurement Techniques

7. ISO 10816-3: Mechanical Vibration – Evaluation of Machine Vibration by Measurements on Rotating Parts

8. ISO 13373: Condition Monitoring and Diagnostics of Machines

9. ISO 1814: Mechanical Vibration – Shock and Vibration Testing of Machines

10. DIN 45669: Vibration of Industrial Machines

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