There are just under 400 wind turbines in Ireland. By 2030, 80% of Ireland’s electricity will be generated by renewables and onshore wind will be the largest contributor of that 80%. It is estimated that Ireland needs about 5,000M/W of power in the form of offshore wind farms to respond to the climate emergency.
The Government of Ireland has recently increased their ambition for 2030, with the aim of providing 7,000 megawatts of offshore wind energy.
It is crucial that these new windfarms are protected against adverse weather conditions such as lightning strikes. Therefore, there must be an effective lightning protection system and earthing system installed.
In this article, Technical Design Manager, Mr Hadi Beik Daraei looks at the facts and solutions around protecting wind turbines against lightning strikes.
Facts and Solutions
After extensive academic and industry research, based on the recorded data in relation to lightning incidents at wind turbines, some facts and solutions have been established as follows.
1. Wind turbines can change the lightning activity that occurs in their vicinity up to a certain distance; meaning the local flash density will be increased. In this regard, local weather, and topographical effects during both warm and cold seasons are the crucial factors to be considered. The basic equation for the number of flashes is:This issue is addressed by ‘Location Factor Cd’ in the standard IEC61400-27. For Wind farms placed offshore, it may be necessary to assign a higher location factor as the possibility of summer storms also needs consideration. The following table represents the typical value of the location factor based on the level of lightning activity and the topographic characteristics.
2. Wind turbines are exposed to many subsequent lightning strikes including short and long strikes, therefore, becoming exposed to encountering different values of energy. In IEC standards, the value of the discharging energy has been clearly stated for negative and positive strikes, as the following table outlines.
3. In all cases, if the following conditions are met, there will be a safe discharging of the lightning current without any incident of fire.
3.1 The Material used for the Lightning Protection System (LPS) components meets the minimum requirement stated in the related standards, IEC 62305 & IEC 62561.
3.2 The interception of a lightning discharge is taken under control in such a way that all possible strikes are received and intercepted by the LPS components designed and considered for each blade. Note: This factor relates to the configuration and design of the Air termination (receptor) system.
3.3 The continuity of the discharging paths is always guaranteed when the earthing electrode system is sufficient to make appropriate contact with the groundmass.
Note: This factor relates to the inspection and maintenance quality and intervals.
Problems with Wind Turbines
A wind Turbine is a facility which is designed to rotate under normal operation. The rotation can impact the interception process of the lightning current. Therefore, the attachment point could be at the surface of the blade instead of the LPS component which is installed on the blade.
Among the three conditions mentioned above to guarantee the safe discharge of the lightning current, items 3.2 and 3.3 may not be fully respected in some situations. Therefore, the wind turbine blade may encounter a fire incident.
To reduce the damaging events for the blade, the below three conditions should be investigated and traced prior to installation of the wind turbines:
- At an early stage of the manufacturing of the blade, the protection methods of the blade must be discussed with the technical engineering specialists about the lightning protection systems. Lightning protection engineering specialists will give their recommendations based on the type of blade and the flash density of the area in line with the requirements stated in IEC 61400-24.
- Specifying the schedule of maintenance and inspection times and intervals.
- Provide an appropriate monitoring system that reflects information on the number of lightning flashes and their severity level.
LPI Group are collaborating with ERICO nVent, who produces the protection components for wind turbine blades. Continuous collaboration and innovations will develop and achieve more robust solutions to protect wind turbines and reduce the risk of fire damage.