Lightning is the biggest threat for wind turbines. Turbine blades and towers are prone to lightning strikes and lightning arresters are not the proper tools to protect the wind turbines against lightning damages.
Lightning usually hits the sharpest and tallest object in an area because ground charges emitted from objects with high elevations reach to opposite charged streamers of the cloud earlier than the charges from any shorter object. On the other hand, lightning current aims to reach ground by following the shortest and most conductive way. That is why, a tall structure such as a wind turbine in a wind farm is the primary target for lightning strikes in an open area.
Wind farm is a combination of many Wind Turbines. Main components of a wind turbine are; 1)Blades, 2)Housing which covers elements such as rotor, shaft, gear-box and generator, and 3)Tower which holds the turbine.
Lightning Threat on Wind Turbines
Elevation of wind turbines reach up to 200 meters with 40 to 140 meters tall towers and 20 to 60 meters of blade lengths. Turbines are generally placed as the tallest structures around in order to avoid any obstacles and have highest efficiency possible. Blades are made of fiberglass composite material, but they are prone to lightning because of the conductive cables inside. Also the tower is made of conductive material and it is also another attractive point for lightning strikes.
Lightning mostly hits wind turbines at the tip of the blades. Blades have copper conductors inside and circular lightning arresters on surface for lightning protection. Purpose of this combination is to attract lightning on the arresters and transfer the current to conductor and finally to grounding system.
However, lightning storm mostly comes with heavy rain and this makes blade surface and interior part wet and conductive enough for lightning current to follow as a path to the ground. Like any other high voltage source, lightning prefers to follow large surfaces and hence lightning current flows on the surface instead of copper conductor inside the blade.
When lightning hits the blade, it damages the tip with stroke effect and quick rise in temperature. Lightning current tries to reach to ground through the fastest way possible and damages the housing and equipment inside such as rotor, gearbox and generator. Finally on the way to the ground, it can damage the transformers at the bottom of the tower.
“Protection” by using Lightning Arresters
Lightning arresters in form of circular metal disks are placed on both sides of blade surface. These arresters are connected to eachother by lightning conductors inside the blade which are bonded together to down conductors inside tower and finally to grounding system at the bottom.
Purpose of applying this solution is to attract lightning on arresters and not to let lightning hit any other spot on blades. However, water collected inside the tips of blade and also on blade surface attracts lightning strike on the tips instead of arresters and damages the blade.
Lightning current may be flowing through conductors inside blade or blade surface after damaging blade tip. In both conditions, it can damage the housing and equipment inside and also can damage transformers at bottom of turbine tower.
With a good grounding system application, damage on housing and tower can be minimized, however studies and field experiences show that this is not enough to protect turbine against lightning strikes and it is an unnecessary risk to attract lightning on turbine blades.
There is definitely a need for a reliable lightning protection system for wind turbines but lightning arresters can not provide this protection because they attract lightning on wind turbine..
Lightning must be kept away from the site.
The best way of being protected from direct lightning strike damages and possible secondary damages by electromagnetic field of lightning current is to keep lightning away from the turbine.
EvoDis® Lightning Prevention System can be applied by replacement of existing lightning arresters on blades with appropriate EvoDis® models and with an additional unit on housing in order to minimize the risk of getting hit by lightning on blades, housing or tower.
While existing lightning arresters use conductors to transfer lightning current to grounding system, EvoDis® units use them to collect ground charges as fast as possible and dissipate them through thousands of tiny sharp points. This process blocks charge emission towards the opposite charged streamers of cloud and makes wind turbine “invisible” to lightning.
EvoDis® Lightning Prevention System is a lightning protection solution with 100% success in high voltage laboratory tests and in field tests. EvoDis® has been applied to hundreds of towers worldwide and none of these towers have been hit by lightning since the dates of installation.
Best way of lightning protection is to stay away from it.
EvoDis® Lightning Prevention System keeps lightning away.