# Fault Diagnosis Approach of Main Drive Chain in Wind Turbine Based on Data Fusion
## 2 Fault Features Extraction of Wind Turbine Main Drive Chain Based on Data Fusion
### Fault Features Extraction of Wind Turbine Main Drive Chain Based on Data Fusion
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Faulty Module** & **Main Fault Type** & **Fault Cause** \\ \hline \multirow{6}{*}{Gear break} & \multirow{3}{*}{Gear break} & Sudden impact overload, bearing damage, shaft \\  & & bending, continuous contact fatigue, foreign matter \\  & & mixed in the meshing area, etc. \\ \multirow{2}{*}{Gearbox gear} & \multirow{2}{*}{Tooth surface wear} & Material defects, poor lubrication, foreign matter mixed \\  & & in the meshing area, etc. \\ \multirow{2}{*}{Tooth surface pitting} & \multirow{2}{*}{Poor lubrication, over-high speed, over-high oil temperature} \\  & & Poor lubrication, over-concentrated local load, over-high oil temperature, over-high speed, etc. \\ \hline \multirow{6}{*}{Bearings ( gearbox, main shaft, generator, etc.)} & \multirow{2}{*}{Surface peeling} & \multirow{2}{*}{Overload, design or installation defect, foreign matter mixed in, over-small clearances, etc.} \\  & & Over-small clearance, poor lubrication, overload, rolling \\ \multirow{2}{*}{Crack} & \multirow{2}{*}{Bonding} & \multirow{2}{*}{Over-small clearance, poor lubrication, overload, rolling body deflection, etc.} \\  & & Crack \\ \multirow{2}{*}{Shafting (main shaft, low/high speed shaft in gearbox, etc.)} & \multirow{2}{*}{Shaft misalignment} & \multirow{2}{*}{Design or installation defect, etc.} \\  & & Material and installation defect, stress concentration is \\ \multirow{2}{*}{Shaft bending} & \multirow{2}{*}{Shaft bending} & \multirow{2}{*}{Ret eliminated during the manufacturing process, gearbox damaged, etc.} \\  & & Material defect, stress concentration is not eliminated during the manufacturing process, gearbox damaged, etc. \\ \multirow{2}{*}{Coupling} & \multirow{2}{*}{Misalignment} & The gearbox high-speed shaft is misaligned with the generator, bearing air gap is too large, the ball is slightly \\  & & Corruded, etc. \\ \multirow{2}{*}{Ginding disc fracture} & \multirow{2}{*}{Safety cover scratch, the high-speed shaft of the gearbox and the generator are misaligned, etc.} \\ \hline \multirow{2}{*}{Generator winding fault} & \multirow{2}{*}{Rotor fault} & \multirow{2}{*}{Rotor eccentricity fault, bearing deformation, design defect, poor installation, etc.} \\  & & Stator fault & Winding insulation aging \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Types and causes of typical faults of main drive chain in wind turbine. Assume that the background noise of the nacelle shaking and vibration under the first section of rotational speed ranges of the main shaft and generator and the wind turbine power up operation state are \(x1(t)\). Fourier transform of \(x1(t)\) is:  
\[F1(\omega)=\int_{-\infty}^{+\infty}x1(t)e^{-j\omega t}dt \tag{1}\]  
This will be used as the background noise of the low-frequency and high-frequency vibration signal of the main drive chain in the first section of the main shaft and generator rotational speed ranges and the wind turbine power-up operation. Before extracting the low-frequency and high-frequency fault features, these background noises are eliminated separately. Extraction of low-frequency and high-frequency fault features of typical faults  
After getting the low-frequency vibration signal and high-frequency vibration signal without background noise in the previous section, the frequency domain analysis method is adopted to calculate the following parameters as the low-frequency fault features: the low-frequency radial vibration, the axial vibration amplitude, and the vibration phase difference of the main frequency band. For high-frequency vibration data, it is necessary to calculate dimensional parameters, such as effective value, average amplitude, mean square error, kurtosis, and slope, and non-dimensional parameters, such as kurtosis index, impulse index, and margin index. With the help of the spectrum analysis method, the radial vibration amplitude, axial vibration amplitude, and phase difference of the main frequency band of each frequency band can be extracted as high-frequency fault features.