Following the catastrophic failure of two Vestas wind turbines on Feb 22 and 23, 2008, the Danish energy agency requested an investigation into the events. A report was produced by engineers at Risø DTU. Below is the report translated into English. The original report, in Danish, can be accessed by clicking on the link below. A video of one of the failures can be seen here: http://www.windaction.org/videos/14294 . It is important to note that the debris from the first turbine failure which occurred on February 22 spread as far as 700 meters away. Risø DTU is formerly a government research institution under the Danish Ministry of Science, Technology and Innovation.

The study conducted at the request of the Energy Agency of the Energy Secretary Approval for Wind turbines in cooperation with Risø-DTU experts.

1) Damage Monitoring of a Vestas 600 kW wind turbine at Halling, Hornslet 22 February 2008, kl. ca. 15.20.

Square with the wrecked mill, which stands at the northernmost of a series of 5 was visited Tuesday morning, 26 February and there has been an informed exporting meeting with Vestas in the afternoon. Events based on information from Vestas and images from TV 2 East and from neighbors.

Description of windmill type:

The windmill is a Vestas (Nordtank NKT600-180/43). The mill was commissioned on 23 December 1996 as the first of a series of 5 mills. The mill is privately owned.

These milltypes - no longer produced - were approved by the Risø. 15. September 1996. (No. B-130-1 REV1).

Events:

Vestas had announced that it was called to service the mill, as a result of defects in brakes function (error: "worn of brakes"). In the previous routine general overhaul the problem was noticed with the main gear støjede part, and it was recommended an endoscope examination be performed.

A Vestas service team was scheduled to arrive Friday morning to check the function of the brakes and monitor repairing and testing of the brakes.

The wind turbine braking function was tested by a grinder cap 8-10 times. After that, the turbine was started again from the bottom of the tower to get it online for normal production. The fan at the time very strongly, and during boot used tip brakes according to information at the meeting with Vestas to manage Roto's revolutions until the operating speed could be achieved. This means that Tipperne was turned off during boot.

At the start of the mill, just as it reads on the web, there was noise from the møllehat-ten and the installer pressed the stop button. The turbine control system initiated controlled stop court proceedings but was immediately followed by a bang (presumably the gearbox was broken). The mill shook vigorously along with the cable holders etc.. rattles off the tower. The rotor stops abruptly for a moment, but were still running so far. Ningstal rotor speed was relatively low, but it was found that the mill could not be controlled from control panel or stopped with the mechanical brake on high speed shaft. The field of safety required that personnel exit the mill quickly. Outside the mill, personnel found that the aerodynamic brakes (pivoting tip) were broken.

The wind blew very strongly, and the mill increased its speed and achieved above-race speed.

Service personnel contacted the police to get off the field. In cooperation with the police, a security zone of 400 meters was established and the neighbors warned. The ne-mode products in ca. 2 ½ hours.

Turbine damaged:

The incident was filmed by a neighbor and some of TV2. The result of the accident is that the wings collapse, the tower was hit and get the "hat" bent upwards (against the wind). Wing Pieces from all three wings spread widely spaced lee of the mill, almost 180 degrees.

Mill hat and the top half of the tower crashed and the generator falls out so that it lay alongside. Larger pieces of wings landed 2-300 meters away, while the smaller pieces estimated to have flown up to 500 meters. There were pieces found at a farm about 700 meters away, but those pieces may have been blown over subsequently, due to the very strong winds at the time.

The bottom half of the turbine tower remained. An inspection of the gears showed that the gears were damaged. No one person is injured.

Evaluation of events:

The likely occurrence is that the gearbox broke, causing a strongly spin which briefly stopped as vingetipbremserne when they were turned off. The brake on the speed of the shaft was out of function due to the fact that no torque could be transmitted through the gearbox.

The wind blew very strongly, so the rotor, which now could not be slowed down, went into overspin. Ry-earth from the blockage has been shaking the ball to fall, thus the turbine emergency power system was activated and functioned as krøjesystemet thus had been inoperative.

From that moment it was, in practice, not possible to manually stop the mill.. The rotor started to accelerate and the hanging Tipperne for conducting lightening broke off and fell to the ground.

From imaging literature (taken from the neighbor's house) one of the turbine blades collapsed, presumably because tipstyret ejection.

Subsequent studies of the gears showed extensive damage. The teeth of the action area were virtually cut off by the ever-rotating high-speed gears.

The accident report was prepared by Report Date: 19 June 2008 for Vestas Technology R & D Denmark by Morten H. Jensen, Advisory Engineer, Leif Hansen Wind Power Technology, Denmark. This report confirms the above events.

The Approval Secretariat's assessment that there is a comprehensive set of unfortunate circumstances, which under the circumstances were difficult to foresee. The process shows that it is important that the turbines are properly serviced by qualified personnel.

2) Assessment of the damage process of a Vestas V47 660 kW at Sidinge 23 February 2008

Description of windmill type:

The mill is a Vestas V47 660 kW. The mill was commissioned in August 2000.

The mill is owned by a turbine Lauge.

Mill type, (no longer in production) was approved by Germanischer Lloyd, 16 June 2000. (No GA-02B-2000).

The event:

Vestas indicated that one wing was broken by early morning on 23 February 2008. The accident was discovered by a neighbor.

The wing was broken at hubs and had hit the ground around. 60 meters from the mill.

It is found that the bolts in the wing bearing were broken. No person was hurt.

Evaluation of events:

Vestas' own inspection of the broken bolts had shown that there were breaches caused by lack of torque at some of the bolts, which over time led to a fatigue fracture, followed by a domino effect on other nails.

Vestas indicated that the failure to feed may come back to moth-lens assembly, and regretted not having identified the problem at the annual check.

Approval Secretariat considers that the described events are likely due to a lack of inspection of the feed on nails which are critical for the mill safety.

Overall recommendations:

It is recommended that the Advisory Committee for approval scheme review and assess hændelsesforløbene as soon as possible and to draw up guidelines to ensure that the type and project approvals clearly show the requirement for ongoing maintenance, which are prerequisites for permitting of the turbine.

Also recommended that the requirement for ongoing servicing and maintenance of wind turbines be discussed as soon as possible by the Advisory Committee for approval scheme and together with the service sector also to ensure that all mills have conducted the necessary service and maintenance needed for quality sound manner.

Windaction.org wishes to express our sincere thanks to Wilfried Heck for providing us with the above translation of the Danish report.

Download File(s):
Endelig redegørelse for haveriforløb ved Halling og Sidinge2.pdf (29.04 kB)