Guest post by Neil Rankine from Groundswell Bass Coast.
On Wednesday (21st March 2012) one of the Wonthaggi wind turbine’s blades was reportedly hit by lightning, causing the blade to split down its length. It’s now hanging from the hub in need of being replaced.
Having one turbine off-line will obviously reduce the amount of electricity the wind farm can produce for a while. Clearly any form of generation will have unforeseen mechanical and other breakdowns so I thought I’d see how often coal plants like Hazelwood in the Valley are generating.
Hazelwood has eight generating units and they always seem to have one off-line for maintenance or repair – sometimes two. The actual figure for achieved generation is a bit under 84% (Google ‘green energy markets hazelwood’).
Coincidently, five turbines out of six still operating at Wonthaggi gives the same figure (83.3%). So the availability of the wind farm is about the same at the moment, as Hazelwood power station. In the long term of course the wind farm will have a higher availability than coal fired generation as there is much less to go wrong.
People often say that governing mechanisms can go wrong with wind farms, another potential cause of blade failure, but the same can, and has happened with coal fired steam turbines.
The difference is that the Wonthaggi wind turbine blade failure takes out 2 megawatts for a month or two while it’s repaired, a turbine failure in the Latrobe Valley could take out 500 megawatts for a year or more.
Of course there’s the old chestnut that wind doesn’t blow all the time and people criticise wind farms for this. But that’s the wrong way to think about wind energy. It’s free fuel energy when it’s available. The other generators can adjust their load to compensate for fluctuations from wind.
The fluctuation over the whole grid is actually small as the wind is usually blowing in one area when not at another. It’s also predictable with good weather forecasting and sensing over wide areas.
Our current coal fired generators can cope with proposed wind farms easily, and when we build them, base load solar thermal generators will work well with wind farms too.
You can check out Dave Clarke’s info on lightning striking turbines at Wind in the Bush, where the photo below comes from.
yes2renewables.org 
Yes, the operators claim a lightning strike, however there is no sign of burning of any sort on the blade core, or on the casing which is lying on the ground at the tower base.
REPower’s MM82 ad states:
Lightning protection
Lightning protection concept conforming to IEC regulations with internal and external lightning protection
External lightning protection system with blade receptors and lightning rod at the weather mast
Reliable protection of bearings due to defined lightning conduits
GFC coupling for the galvanic insulation of the generator system from the gear system
Over-voltage arrester protecting the electric system
Reliable protection of the generator by means of insulated bearing bushings.
If it was a lightning strike, the lightning protection system didn’t work too well!
John,
Thanks for pointing this out.
As you kindly note with your wording from the MM82 ad the lightning system protected the electric system. Did the turbine burn down? Perhaps the lightning protection system is designed to conduct the lightning to earth. Strange eh?
Seems to me the lightning protection performed its function exactly as it was supposed to.
From my Wonthaggi contact:
“Hi Blair, I went down and had a look day before yesterday, the blade is layed up fibreglass with apparently no frame or even ribbing (looking from a distance anyway). They wouldn’t be very heavy I’d imagine. Met one of the REPower tech people there, he said their only difficulty will be booking a crane as there are so many projects on the go it’s hard to get any crane. They apparently only need a crane to hub height so nothing too specialised. The blade is very strong around the hub and so the rest of it was split and frayed but still hanging on other than one sizeable chunk that landed just at the base of the tower.
They have 74 of this type of turbine in their farms and haven’t had a blade problem before he said, he reckons they are great units. Almost certainly lightning he said given the storm at the time, but they will investigate a bit later when occ health etc.”
No-one seems game to comment on or refute fact there are no burn marks anywhere. Virtually anything struck by lightning has residual burn marks.
John, I think the appearance of burn marks is dependent on the material being struck and possibly the surface conditions i.e. moisture, dust etc. I have seen a hayshed that had a nice hole punched through the corrugated iron roof near one of the vertical metal poles supporting the roof. There was no sign of burns in the iron but you could see a burn mark running down part of the metal pole. I realise my comments are only anecdotal but it did illustrate to me at least, the weird aftermath of a lightning strike.
John it’s an interesting question. However, are you sure that lightning always leaves burn marks? Just googling it, here’s one site – about aircraft being struck:
http://www.newton.dep.anl.gov/askasci/wea00/wea00024.htm
“A lightning strike on an aircraft normally does not damage the airplane, although it may leave a burn mark.”
I would be concerned if tall structures in open fields didn’t get hit by lightning? big deal.
The issue with wind turbine blades struck by lightning is if there is moisture in the blade. The blades are designed to cope with lightning strikes, and usually there is just a small burn mark at the lightning receptor where its struck.
If there is moisture, this can be superheated by the lightning, and the steam is what split and destroys the blade. All the photos and descriptiosn I’ve seen are consistent with this, and there will be very little burning.
“Back in the day” was part of the design & construct team, Jason has it right, the lightning arrest system appears to have worked however with so much energy being dissapated the blade struture has suffered accordingly. Blair’s discussion with the tech would also be fair comment, finding a spae crane is probably the biggest issue, they are all on mine sites.
the blades failed due to a small crack water got in’. all of the other 5 have been strengthen at weak pont .see test patches on old ones lying on ground.