Full name of DESMe project is "Development of an expert system for measuring lightning strike parameters and protection of wind turbine blades to reduce failures and downtime."

With a rapid growth of the wind power capacity in the world, the damages caused by lightning activity received more attention, especially in the regions with intense lightning activity. Wind turbines are high structures, installed in isolated places, often at higher altitudes where wind as a primary energy source is significant and where thunderstorms also occur more often. Given the height and micro-location of wind turbines, it is certain and inevitable that they will be struck by lightning. The most common damage caused by lightning is the failure of low-voltage equipment and control systems within the wind turbine, whose insulation levels are low, while the blade damage is the most expensive.

Despite the existing lightning protection systems and overvoltage protection, failures on wind turbines still occur. The most significant number of damages was reported in areas with high winter lightning activity, such as Japan, Brazil and the Mediterranean, which includes coastal Croatia, which is exactly where all Croatian Wind Power Plants are installed. During winter when the thunderstorm clouds are lower, the waveforms of lightning currents are different from those that are statistically the most common and considered in recommendations defined in the existing lightning protection standards. When high lightning activity is additionally combined with high soil resistivity at wind turbine micro-location, it is difficult to satisfy the grounding system requirements.

Due to repeatedly reported damages, it is important to determine the exposure of an individual wind turbine to direct lightning strikes and adjust the maintenance of the lightning protection system. To estimate the exposure of wind turbines to direct lightning strikes, it is possible to use data from the lightning location system. The data from the lightning location system showed a significant increase in lightning strike density at micro-locations after wind turbine installation, meaning that wind turbines attracted strikes that would otherwise be scattered over a wider area in vicinity. However, the data from the lightning location systems does not give a total insight into wind turbine exposure to lightning strikes. In addition to roughly defined equivalent  attraction areas, the main cause are the upward strikes initiated from the blades. Unlike in downward lightning, upward strikes always have the initial continuous current (ICC), which lasts relatively long and has low amplitudes (tens to hundreds of milliseconds and 100 A to a few kA). If there is no superimposed fast rising and high peak current impulse, these lightning events are not detected by the lightning location systems due to their very low frequency electromagnetic fields and their weak peak current amplitude. Due to the long duration of upward strikes, the transmitted charges during one strike can be over 600 C. For understanding the severity, the protection class I implies a maximum transmitted charge of 300 C. Therefore, the ICC strikes are recognized as the principal cause of damaging and melting of the lightning protection system components. Their effect is cumulative, and it would be useful to adjust the maintenance of the lightning protection system according to the number of such strikes, i.e. according to the total transferred charge. For a complete insight into the lightning protection system stress, it is necessary to know the lightning waveforms and lightning current parameters such as front time, transmitted charge and current amplitudes.

The aim of this project is to develop an expert system for measuring lightning current parameters that strike wind turbine blades in order to obtain the necessary data for the improvement of lightning and overvoltage protection. The prototype measuring system will be installed at one wind turbine, on which the recorded measurements will be monitored and processed. In addition, lightning strikes to the same wind turbine will be recorded by a special high-speed camera, as a confirmation of the lightning event and lightning type (downward / upward). The specific objectives of the project are:

• automated collection and processing of waveforms of lightning strikes that hit wind turbines;

• processing of the lightning data to determine the specific characteristic of the lightning in the coastal area of Croatia;

• development of wind turbine models in EMTP, simulation of measured strikes, comparison with measurement;

• final recommendations for lightning protection system improvement, defining desirable characteristics of the protection system based on measured strikes’ characteristics.