# Fault Diagnosis Approach of Main Drive Chain in Wind Turbine Based on Data Fusion
## 3 Fault diagnosis of Wind Turbine Main Drive Chain Based on Fusion of Two Types of Data
The actual data from 2 May to 29 June 2019 are a total of 2000 pairs of fault characteristic data, of which three-quarters are used as the training set of the main drive chain fault diagnosis DA model while the rest are used as the test set. The number of hidden layers of this DA model is set to 17 while the average absolute error of the overall data set is the smallest, and it has the greatest ability to excavate deep features of the input data. The number of hidden nodes in each layer of the DA network are set to 152, 314, and 528, with the consideration to minimize the mean absolute deviation (MAD) and loss indicators. Because the data sets of the main drive chain under normal operating status are used for the construction of DA model, the reconstruction error under abnormal states is great enough to exceed the monitoring threshold under normal states. After the training of the fault diagnosis DA model, the test set data are used to test the gearbox broken tooth diagnosis model, and the verified results are shown in Figures 8 and 9. Figure 6: Monitoring platform in operating status. Figure 7: Fault diagnosis module of the monitoring system. As shown in the figures above, before the gearbox teeth of the main drive chain of the wind turbine A and B are broken at a data point of about 150, the model output was within the monitoring threshold range, and the fluctuation range is not large, indicating that the main drive chain gearboxes of the two turbines are operating in normal states. However, the output of the model begins to increase and exceeds the pre-set monitoring threshold after the tooth break. Hence, it is judged that the two wind turbines are malfunctioning, and fault diagnosis as well as early warning are performed. Consistent with the actual data, the time domain and frequency spectrum diagrams of the vibration signal of the medium-speed shaft of the gearbox of turbine A (9 May 2019) are shown in Figures 10 and 11. Contrastively, the time domain and frequency spectrum diagrams of the vibration signal of the medium-speed shaft in the gearbox in the early warning state (12 May 2019) are shown in Figures 12 and 13. Figure 8: The output of gearbox broken tooth diagnosis model before and after gearbox tooth break of wind turbine A.  
Figure 9: The output of gearbox broken tooth diagnosis model before and after gearbox tooth break of wind turbine B. As shown in Figures 10 and 12, the time domain diagrams under the normal and warning conditions are similar and show little valuable information. However, the hidden differences can be clearly revealed in the diagrams of the frequency spectrum in Figures 11 and 13. The details are described below. Figure 13 shows a sideband modulation signal of 5.99 HZ (signal in the red box in Figure 13) at a rotational frequency of the medium-speed shaft near the gear mesh frequency (670.833 HZ) from the medium-speed shaft to the high-speed shaft of the gearbox. However, there is no sideband signal such as this under the normal operating state in Figure 12. This difference can be judged as an abnormal condition of the meshing gear of the shaft. The operation and maintenance personnel disassembled the on-site gearbox and found that the  
Figure 11: Frequency spectrum of vibration signal at the medium-speed shaft position in the gearbox of wind turbine A under normal conditions. Figure 10: Time domain diagram of vibration signal at the medium-speed shaft position in the gearbox of wind turbine A under normal conditions. fault was the breakage of tooth on the medium-speed gear, as shown in Figure 14. This model correctly warned the early fault of the main drive chain gearbox of turbine A and avoided further expansion of this failure. Figure 12: Time domain diagram of vibration signal of medium-speed shaft position in gearbox of wind turbine A under warning conditions. Figure 13: Frequency spectrum of the vibration signal of the medium speed-shaft position in gearbox of wind turbine A under warning conditions. The details of all experiments are not shown completely here.