# Detection of Wind Turbine Failures through Cross-Information between Neighbouring Turbines
## 2 Preliminary Observations  
When observing and comparing the evolution over time of the same variable for all wind turbines operating correctly in a wind farm, a clear pattern of change can be noticed. This result is expected as the turbines are identical and are so close geographically that the operating conditions are very similar between them. Furthermore, the SCADA data are averages of the variables over 5 min (in our data), so that the higher frequency variations are lost in this operation.  
Thus, although this pattern of joint variation appears in all the variables, it becomes highly evident when the represented magnitude is of slow variation, as in the case of temperature or pressure measurements.  
To illustrate the coupling of the signals through a representation, the evolution of the same variables in perfect time alignment is depicted to see the near-ideal synchronisation when the WTs are working correctly, but are decoupled otherwise. This observation is fundamental to develop a method based on neighbour observations.  
Figure 1 shows, for the same time interval, four magnitudes of the generator system of all the turbines of the park. The first signal corresponds to an angular velocity: _wgen_avg_RtrSpd_IGR_ and the lasts three signals correspond to the temperatures: _wgen_avg_GnTmp_phsA_, _wgen_avg_GnTmp_phsB_, _wgen_avg_GnTmp_phsC_. In fact, these are the first four variables that appear in the database. See Section 3 for an explanation of the names of the variables.  
The upper graph in Figure 1 shows the rotor speed _wgen_avg_RtrSpd_IGR_ of all superimposed wind turbines in perfect time alignment, following a switching pattern due to the presence of wind that causes the wind turbine to produce power or to be stopped. It is interesting to note that, while the magnitudes of the well-functioning machines fluctuate similarly, the WT82 (in yellow) is decoupled from the general operation for a time interval. That is, during a time interval the values of the WT82's signal _wgen_avg_RtrSpd_IGR_ take values close to zero, indicating that the turbine shaft does not rotate (it is stopped), when the rest of the turbines maintain a pattern of activity. From now on, this signal will be used to determine the status of the WTs. The next three signals in Figure 1 are the temperatures, which are closely coupled to each other in such a way that it takes careful observation to see that they are different. Thus, it can be observed that the temperature of turbine WT82 drops to room temperature levels during the interval where the rotor speed of WT82 (the signal _wgen_avg_RtrSpd_IGR_ in the upper plot, also in yellow) becomes zero, indicating that the turbine, despite the wind blowing, has been stopped, possibly due to a fault.  
This observation illustrates that when the WTs work correctly, the magnitudes collected by the SCADA evolve synchronously between them, but when this is not the case, this synchrony is disrupted, and the signal _wgen_avg_RtrSpd_IGR_ is useful to determine the WT state.  
Figure 1 also points out two typical problems that appear in the SCADA databases. The first one is the presence of outliers and the second one is the lack of data in certain periods due to the failure of the SCADA system.  
In Figure 1, especially in the three temperature plots, the outliers are easily identifiable due to the physical impossibility of such a large variation. In this case it seems that the data has been poorly transmitted since each WT that presents an error--an outlier--is simultaneously shown in all the signals. Note that the outlier is represented by a certain colour (which also identifies each turbine). When the fault affects a magnitude of the turbine but not the rest of magnitudes, the fault can be attributed to a sensor fault. In Figure 1, a general failure of the SCADA system can also be noticed, because there is a time interval in which no data is recorded, affecting all the magnitudes of all the turbines.