Reducing blade damage and costly downtime

Wind Turbine Lightning Protection Systems

The most common lightning protection system (LPS) uses one or more surface mounted receptors connected to a down conductor. A typical lightning strike begins when the strong electric field induced by a charged storm cloud causes an upward leader to emanate from the receptors in the blade. A direct strike results when one of the streamers connects with a downward leader from the cloud, passing a large amount of electrical and thermal power in a short time through the turbine.

The Problem

The problem arises when streamers originate from the down conductor or other metallic components inside the blade. Often those streamers evolve into leaders that connect with the downward leaders from the cloud, and the resulting strike can cause significant blade damage. At best, this leads to blade punctures; but more significant damage – from split trailing edges to total blade destruction – is often seen at wind farms where there is a lot of lightning activity. Many farms in the interior of the U.S., for example, report that lightning damage is the number one or number two cause of turbine downtime and repair costs (the other being leading edge erosion). And even when the internal streamers do not lead to a direct strike, they can still penetrate the skin and weaken the structure. Over time, this can make the skin electrically porous, making it more susceptible to lightning damage.

The ArcGuide® Solution

Whenever there is lightning activity surrounding a wind turbine, there is a competition between the streamers that form inside the blade and those that form at the lightning receptors on the outside surface of the blade. The ArcGuide® coating modifies the surface of the blade to make it more likely that the streamers that form at the receptors will “out compete” the interior streamers and be the first to connect with the lightning leaders. The ArcGuide® coating consists of a proprietary formulation of discrete conductive elements combined with a polyurethane topcoat paint. Here, topcoat refers to the outer, final paint layers applied to the blade that protect against environmental effects, including rain erosion, UV degradation, and particle impacts. The ArcGuide® coating protects against these threats, with the added feature that it enhances the performance of the LPS.

Promoting Surface Flashover

The ArcGuide® coating promotes the formation of a “surface flashover” in the vicinity of the lightning receptors, which is an ionized channel in the air adjacent to and above the surface. This ionized channel ensures a safe passage of the lightning charge through the air to the lightning receptor and on to ground via the down conductor. The coating works by locally enhancing the electric field immediately above the blade’s surface. The local surface spots that see an increase in electric field strength then become the first to surpass the ionization potential for air, resulting in regions of corona along the blade’s exterior surface. As the electric field strength increases, those regions of corona connect, resulting in a surface flashover and a streamer that propagates away from the blade, thus reducing the field intensity around other conductors located inside the blade. In this way, it allows the streamers on the outside of the blade to “win the race” to connect with the downward leaders from the cloud.

Enhanced Streamer Activity

One proof of concept of the ArcGuide® coating is demonstrated in this photograph. In this experiment, the ArcGuide® coating is applied to one half of a two-foot by two-foot square fiberglass panel, while the other half is covered with a common wind turbine blade topcoat (“Baseline Topcoat”). The panel is then subject to a high electric field. In the split second prior to flashover, multiple streamer paths form on the ArcGuide® coated half, while only a single streamer path forms on the half coated with the baseline topcoat. This behavior shows how the ArcGuide® coating encourages flashover across the surface to the receptors.

Validation Testing

The ArcGuide® coating was developed over a three-year period in coordination with a leading lightning test facility in Pittsfield, MA. In two parallel field tests, the coating will be installed on a total of eight wind turbines at two wind farms under the management of two large owner/operators in the interior of the U.S. in 2022. Funding for the development and validation of the ArcGuide® coating was provided by the U.S. Department of Energy and by the Rhode Island Commerce Corporation.

The ArcGuide® Kit

Each ArcGuide® kit consists of about 1 kg of coating, sufficient for coating the recommended surface area near the tip of one blade. Each kit comes with detailed installation instructions customized for each blade model.

Download the White Paper for more details about the development and validation of the underlying technology.

Now available as the Mankiewicz Alexit® BladeRep® Topcoat ALP 20 with ArcGuide®.

Schedule a briefing for more information on how to protect your wind turbines from the threat of lightning!