Page 47 - North American Clean Energy May June 2015

wind power

Six Striking Facts about

Lightning and Wind Turbines

By Alex Byrne and Matthew Malkin

Modern wind turbines are typically equipped with a lightning protection system (LPS). Internationally recognized standards
require that the LPS should intercept and conduct the vast majority of strikes without damage to the turbine, yet insurance

companies are reporting 20% of all wind project claims are due to lightning damage. Lightning has become a signiicant

source of higher than expected costs and downtime in the operation of some wind farms. hough much is still unknown about
lightning interaction with wind turbines, there are six facts worth knowing.

Some damage is expected, even with LPL 1
focused on conduction, because little can be done to ield-test interception, and

Most modern turbines are equipped with a LPS designed to Lightning Protection Level maintenance is limited to ensuring LPS components such as receptors, diverter strips,
(LPL) 1, the highest level of protection in the IEC 61400-24 standard1. his does not mean and metal caps or tips are in good condition. Nevertheless, most common types of
the LPS should, or will, protect the turbine from all lightning damage. A LPS designed to lightning damage are delamination, disbonding, or incineration of the blade structure
LPL 1 is not expected to protect against extreme lightning events, which can be expected near the tip, which can be attributed to insuicient interception performance.

in about 1-10% of all lightning strikes depending on the lightning environment. Less Interception performance is primarily inluenced by blade design and LPS design,
extreme events should not cause function-impairing damage to the turbine, if the LPS is including material selection, LPS component placement, and electrical insulation.
performing as expected, but are still expected to cause minor damage.
LPS design, carbon iber, tip height, and terrain inluence

A lash density map is not enough to characterize a lightning damage rates
environment
he lightning environment and LPL are not the only considerations when estimating
A lash density map will show an average number of lightning lashes per area (km2 or the frequency of function-impairing lightning damage at a particular site. LPS design,
miles2) per year. However, local inluences such as terrain, speciic storm pathways, and manufacturing quality, and installation are all inluencing factors. Additional inluences

presence of tall objects (such as wind turbines) will afect the localized lightning lash include presence of carbon iber in the blades, tip height, and terrain. Turbines on the
density. In some cases, using a lash density map to determine lightning lash density at a tops of hills attract more lightning than turbines on lat terrain.
particular site could produce errors from 10-100%, or more. It is recommended that site- Lightning interaction with wind turbines is presently poorly understood but
speciic historical lightning data be used to characterize the lightning at a site, preferably knowledge is evolving. While it is possible to calculate the risk of lightning damage5,

over a period concurrent with wind turbine operation or, for pre-construction assessments, industry understanding of lightning interaction with wind turbines continues to
adjusted to account for the future presence of wind turbines.
increase. With that increased understanding, comes improvements in new LPS
designs, as well as further evolution of governing standards, such as the IEC 61400-
Not all lightning can be detected by the NLDN
24, a new edition of which is currently in work. For wind projects that are operating

he National Lightning Detection Network (NLDN), which supplies the majority of now, engineering and installing efective retroits for an underperforming LPS is a
lightning data in the U.S., reports a 95% detection eiciency (DE) throughout most of challenging undertaking.
North America. DE is the fraction of lashes observed by a lightning location system As understanding of the interaction between lightning and wind turbines increases,
(LLS) like the NLDN, and is a measure of performance of that system. here is more than LPS technology should progress and performance should improve. he current practice

one type of lightning; the reported DE is only relevant for downward lightning. Upward of writing of lightning damage as force majeure obfuscates responsibility and slows
lightning is an important piece of the wind turbine lightning damage puzzle. hough
innovation in LPS design. Appropriate allocation of the costs of damage will help move
the NLDN is one of the best-performing LLS in the world, it does not capture all upward LPS design forward, which would certainly strike anyone as positive progress for the

lightning events. he actual DE for upward lightning is not well-understood, but one wind industry.
study2 showed a DE of about 37% at a site in Austria. More research is required to fully
understand how much upward lightning can be detected by the NLDN.
Mr. Malkin has 20 years of engineering experience and six years of wind energy
experience, with a focus on blade technology. He has participated in and led

Turbine rotation may increase the prevalence of lightning strikes
multiple blade failure investigations, blade manufacturing quality reviews, and
Recent studies3 indicate that the rotational motion of a turbine’s rotor makes it more technology reviews.
attractive to lightning strikes. Lightning researchers commonly use rockets attached to
a thin wire to trigger lightning during storms for studies4. Similar to the rockets, blade Ms. Byrne has 13 years of engineering experience and nine years of wind energy

tips travel at speeds of up to 200 mph (322 km/h) toward the clouds during the upward experience, with a focus on wind turbine loads, life assessment, and turbine
sweep of the rotation. Rotor motion may incite lightning and increase the probability of performance. She has participated in and led technology evaluations, site
a lightning strike to the blade. hough the research is preliminary, sites with signiicant suitability assessments, lightning analysis, and failure investigations.
lightning damage may want to experiment with shutting down select turbines during

storms to limit lightning damage.
DNV GL | www.dnvgl.com

Interception is not conduction
Conduction eiciency refers to the LPS’s ability to conduct current to ground, while

interception eiciency refers to the LPS’s ability to cause a strike to attach to the turbine
at an LPS receptor. hese functions are separate. LPS testing and maintenance is often

1. International Electrotechnical Commission (IEC) 61400-24: Wind Turbines – Part 24: Lightning protection. Edition 1.0, 2010.
2. Diendorfer, G. Application of Lightning Detection Network Data for Lightning Research and Lightning Protection. International Lightning Detection Conference 2012.

3. Montanya, Joan, et al. Lightning Discharges Produced by Wind Turbines. Journal of Geophysical Research: Atmospheres. 16 Jan 2014.
4. Qie, X. Triggering Lightning Experiments: an Efective Approach to the Research of Lightning Physics. Journal of Aerospace Lab. Dec 2012.
5. Byrne, A., Malkin, M., Field Performance Assessment of Wind Turbine Lightning Protection Systems: Uncertainty due to Upward Lightning and Other Factors, 23rd International Lightning Detection Conference, Tucson, AZ, 2014.

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