Focus: vibration analysis of wind turbines
News - 9 October 2019
VALEMO regularly brings to light its last case studies.
You can find below a full record of the topic “vibration analysis of wind turbines”.
A wind turbine is a rotating machine whose rotation is ensured by mechanical elements found throughout the kinematic chain (see illustration below) : main bearing of the low speed shaft, bearings and gears of the gearbox, bearings of the generator.
Alexis LEBRANCHU. PhD thesis, Université Grenoble Alpes, 2016.
A rotating machine in operation vibrates and vibration analysis makes it possible to detect mechanical defects as part of conditional & predictive maintenance.
1/Vibration analysis from the Fourier transform, from the time domain to the frequency domain
> Accelerometer: a time-based representation
Vibration is studied by observing the variation in the position of a system with respect to its state of equilibrium over time and in a direction of space. It is also interesting to study the temporal derivatives of the position (velocity (first derivative) and acceleration (second derivative)).
To study vibrations on a wind turbine, accelerometers are installed on different parts of the powertrain (see illustrations below) :
> The Fourier transform: a frequency representation
The temporal representation provides a wealth of information that can be difficult to exploit directly. Moreover, many phenomena naturally occur in the frequency domain and not in the temporal or spatial domain. For example, the human brain performs a frequency domain analysis to recognize a voice (auditory signal). The Fourier transform allows to pass from the time domain to the frequency domain (see illustration below).
2/ Acquisition and data analysis:
a centralized telecommunication architecture with adapted software
A wind turbine is generally equipped with 8 accelerometers (2 on the low speed shaft, 4 on gearbox and 2 on the generator) which are connected by cables to an acquisition unit. Then the data pass through the wind site’s intranet network and the Internet network to be stored on the operator’s server. These data are then processed by operating software where the kinematics of each wind turbine is entered (see illustration below of a GE ECO80 wind turbine kinematics performed on the SKF @ptitude Observer software) and analysed by vibration experts.
An essential skill for a responsible operator who is acquired with patience
We have been working for several years now on the development of this vibration analysis skill, which is certainly acquired with patience, since it is so difficult to conclude with caution and precision about the appearance of a defect but also to define the corrective actions resulting from it.
In addition, equipping wind turbines with such systems requires trained personnel and maintaining these systems requires continuous attention.
Thus, we have recently equipped 23 ECO80 and AW1500 wind turbines on 4 wind farms in France with the same vibration system in order to guarantee a homogeneity of the tool used. This development has borne fruit insofar as it has enabled us to anticipate the failure of main bearings (see illustrations below of the low-frequency spectra of vibrations on a main bearing produced on the SKF @ptitude Observer software) and to organise their replacement (supply, logistics, etc.).
In the context of optimizing wind turbine production but also in a broader issue of extending the life time, vibration analysis is an essential element in the operation of projects. Nevertheless, the development of this competence must be done with method and rigour in order to be able to deliver a reliable and effective diagnosis of mechanical defects.
J. Dalmas – Services manager – VALEMO
A. Lebranchu – Doctorate in R&D project engineering – VALEMO
– Internship report for the end of the study period at Ecole Centrale de Nantes – Aymeric Bigourdan.
– Course “Principles and tools for analysis and measurement” of the Conservatoire National des Arts et Métiers – C. Zerrouki.