How can a windmill break? ‘never experienced’

• Arnold Steel

  Online publisher

Is it safe to walk past windmills or live next to them? One broke off yesterday in Zeewolde after which debris left a deep crater in the adjacent road. No one was hurt, but things could have been different. Four questions and answers related to this incident.

Maurik Ankersmit of Dutchwind BV, a company that dismantles and resells wind turbines, thinks something was overlooked during the inspection of the wind turbine. “I can’t see it very well, but it looks like the shaft broke at a flange, part of the windmill where two parts are bolted together. If that happened, they should have seen it during an inspection.”

Wind energy professor Gerard van Bussel also believes that the last inspection of the wind turbine, which according to Vattenfall was carried out in December last year, was not done properly. “It is clear that they have not correctly assessed the condition of the windmill, because then it would no longer have been allowed to operate.”

He says the mill should never have broken in yesterday’s weather conditions. “There was a force 6 wind, and obviously it’s not an extremely strong wind. A windmill should be able to handle it well. After all, the other turbines are still there.”

According to Ankersmit, this type of windmill may be more vulnerable due to its design. It is a turbine with two blades. “They are less stable in rotation than wind turbines with three blades. This releases more vibrations into the shaft, which is therefore under more pressure,” he explains.

Ankersmit thinks the excessive vibration caused the mast to collapse, though he’s not sure. “It obviously remains speculation at this point, and only an investigation can show what really happened.” He says it’s special to see a windmill break down. “Sometimes the blades fall off the turbines, but I’ve personally never seen a whole windmill break down.”

Are these windmills safe?

The windmills along the Eemmeerdijk, built by the now bankrupt NedWind, have been around for about 25 years. They have had more problems. For example, a year after construction, the blades had to be returned to the factory due to hairline cracks, and in 2006 one of the windmills was in danger of falling in a storm. The same year, another was struck by lightning, leaving hundreds of debris strewn across a nearby field.

The damaged mills were dismantled and did not return.

Vattenfall says the remaining 17 turbines received special counters in 2006 that record vibrations. “So far nothing unusual has been seen. It is therefore too short-sighted to say that the latest accident was due to defective bolts or a faulty inspection. The cause of what happened will have to be revealed by the investigation,” says a spokesman. for the energy supplier.

Regular maintenance is performed on the blades of these windmills, he continues. When they are somewhat larger, cracks may appear which, according to Vattenfall, can be repaired. “It’s quite normal in the industry to do this on a regular basis.” Also, bolts would be replaced as needed.

The sixteen turbines still standing along the Zeewolde Dam have now been shut down as a precaution. According to Vattenfall, they are inspected for safety before running again.

The rotor, blades and shaft fell off:

The Zeewolde accident is not the first accident involving a windmill. In 2000 a turbine broke down in Wieringerwaard and four years later the blades of a windmill broke down in the Waardpolder. In 2009, a blade ended up on the A6 highway near Lelystad. The blade broke a windmill from Harry van den Kroonenberg park, he said Flevoland broadcasting. No one was injured, which according to the firefighters was a miracle given the late afternoon time.

Energy supplier Nuon – which was subsequently taken over by Vattenfall – therefore shut down all wind turbines in the park as a precaution. An investigation showed that the blade broke due to a lightning strike. Since the park consisted of old windmills, it was decided to demolish them a year later.

According to Professor Van Bussel, older wind turbines are generally safe. “In principle yes, provided the owner complies with the inspections and maintenance. And Vattenfall will be fine, I guess.” However, he advises that the Eemmeerdijk wind farm should also be demolished, “those wind turbines have been written off”.

Van Bussel supports an annual inspection of wind turbines, carried out by an independent body. Especially for turbines older than twenty years, because they are more susceptible to defects. “The inspectorate of the human environment and transport could do it, for example. He already does it for planes and ships, but not for wind turbines.” The professor hopes that the event in Zeewolde will change things.

Dutchwind’s Ankersmit thinks change is imminent. “The fall of this tree will probably have an effect on the Dutch windmill world. There may be rules about stricter inspections or how long such a thing can stay there at most. After such an event, the government cannot sit still , it seems to me.”