2009-02-02 S-02872-012 Final Report -...

ENERCON Service Center – Customer Relations – Dornumer Straße 20 – 26607 Aurich – Phone +49 4941 976 385 Fax +49 4941 976 319 – Email: [email protected]

Final Report

pages: 78 Contents:

1. Data of WEC 2. Status and operation data before occurrence of damage 3. Extent of damage / damage symptoms 4. Immediate action 5. Root cause analysis 6. Surface measurement 7. Preventive measures 8. Corrective action required 9. Annex Annex 1: Report Ws 10min table Annex 2: Report status data Annex 3: Rotor blade connection system Annex 4: Results of the evenness measurement + 2 pages: Test setup (only in German available!)

Annex 5: Noise sensor Annex 6: Pictorial documentation Annex 7: CE Conformity (+1 page Original) Annex 8: Checking reports

Annex 9: Report status data

1. Data of WEC

Serial no: 481554 / Turbine No. 12 Site address: Fen Farm Wind Park; Fen Lane, Conisholme; Lincs, LN11

7LU Customer: Next Generation Ltd. Type of WEC: E-48 Type of control: CS48a Energy yield: 1,823,340kWh Operating hours: 6,863h Time of damage: 2009-01-04 / 06:26:07 Status signal: 73:02 / Torque Monitoring : Peak Load

Vibration sensor trip, turbine shutdown, automatically and sent SCADA warning message to service control – service crew despatched immediately to site and on arrival found one blade had detached from turbine and had fallen to the ground and one other blade had a damaged tip but still attached to turbine.

Damage at WEC with serial no:

481454 / S-02872-012

Editor Hermann Bohlen / Stephan Menzel / Rainer Schwieters Date 25.02.2009 Subject Blade damage

ENERCON GmbH . Registered Place of Business: Aurich . Commercial Registration No. HRB 411 (Court of Aurich) Managing Directors / CEOs: Mr. Aloys Wobben . Mr. Hans.Dieter Kettwig

Bank Account No.: Oldenburgische Landesbank . Swift Code OLBODEH2 . IBAN DE54 2802 0050 8424 1991 01 . Commerzbank . Swift Code COBADEFF284 . IBAN DE88 2844 0037 0491 4560 02 . Deutsche Bank AG . Swift Code DEUTDEHB284 . IBAN DE41 2847 0091 0060 62002 01 . Sparkasse Bremen . Swift Code SBREDE22 . IBAN DE03 2905 0101 0001 6312 33 . ABN AMRO Bank N.V./Germany . Swift Code ABNADEFF FRA . IBAN DE61 5023 0400 1028 0050 08 . Landes-bank Baden.Würtemberg . Swift Code SOLADEST . IBAN DE97 6005 0101 0002 4834 50 . VAT.Number DE 181 977 360

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2. Status and operation data before occurrence of damage At the day the damage occurred the wind turbine was running with an average power output of 366 kW and a wind speed of 7,1m/s. Maximum data at that day were about 575kW and 9,4m/s (Annex 1). There had not been a single fault message from the WEC which could have been a sign of foresee-able damage (Annex 2). In addition to that, there was no ice at the rotor blades detected on any of the 20 turbines prior to the event. In case of ice detection the control system would generate main status 14 (Annex 9). 3. Extent of damage / damage symptoms On 4 January 2009 a rotor blade aborted from WEC 481454 during operation. The stud connection between the blade and the blade adapter had failed. The sectional view of the connection shows the position of the stud (Fig. 1). The connection consists of 32 studs (Fig. 2 and Annex 3).

Fig. 1 Fig. 2



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The studs show different fracture patterns along the circumferences with a classical fatigue breakage loss profile (Fig. 3)

Fig. 3

View of Blade Adapter Flange (Fig. 4)

Fig. 4



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Breakage of the rotor blade resulted in heavy consequential damage to the nacelle (Fig. 5) and paint damages because of the loosely rotating parts (studs) in the hub (Fig. 6).

Fig. 5

Fig. 6



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4. Immediate action As an immediate action, the entire wind farm were stopped and inspected by Service personnel. In the setting of this inspection, all stud connections between the rotor blade and blade adapter were checked for proper tightening of torques.

As a result of the inspection we considered the re-start of the wind farm and put them back into op-eration for a safety run. All other components (foundation, tower, machine house) have been e.g. inspected visually for po-tential damage. 5. Root cause analysis The first step was to check the durability calculations for this type of stud connection. No errors were detected. As a matter of course, these calculations had been checked by an independent certifica-tion office in the setting of the type certification process. Furthermore, at no time during any previous service activity up to occurrence of the damage was there any indication that fasteners might fail. As mentioned before, the studs show different fracture patterns along the circumferences with a classical fatigue breakage loss profile (Fig. 7).

Fig. 7

To determine the cause of damage the pressure flange with the cut piece of the rotor blade was ex-amined. The pressure flange is a two-part Glass fibre-Reinforced-Plastic-ring which is glued in with a posi-tioning device, so that a plane surface of the rotor blade is formed. In the course of examination this surface was checked on its evenness.



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6. Surface Measurement Measuring procedure: Photogrammetry (exactness 0, 05 mm)

• System AICON DPA Pro

• Measuring unit with a length of app. 1340mm

• The interpretation was done by Program Comet Inspect V1.01 Measuring points were glued on the flange surface to measure it by the medium of Photogrammetry. It was impossible to measure all positions due to the fact that some areas were heavily damaged because of the impact. The results of the measuring are enclosed (Annex 4). Final conclusion It is clearly visible that there is a step of the segments at both joint positions. As a result a gap arises between blade flange and blade adapter across many studs at one side of the joint. This gap results in an increase of tension ranges at the studs and this leads to a decrease of lifetime. On the site of the joint with the maximum tensile strength the damage starts and the stud cracks as a fatigue break (Annex 4). As soon as a stud breaks a further load increase of the surrounding studs follows so that a “zip-effect” arises and the studs will break one after another. The rest of the studs will then break by a forced fracture. The public initial reports and remarks concerning an extraneous cause by third parties e.g. flying objects are already and definitely excluded. 7. Preventive measures As an immediate action, the stud connections at all blade adapters in the entire wind farm were checked for a 100% proper tightening of torques. No further preventive action will therefore be necessary and the turbine can stay in safe and reliable in operation.



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8. Corrective Action required In addition to that all joints between blade flange and blade adapter were determined concerning possible gaps. Therefor, we measured all values in a 6 o’clock rotor blade position. For measuring we used a feeler gauge 0,1mm to check for a gap on the joint between blade adapter and rotor blade from the inside and outside. The maximum measuring depth should not exceed > 40mm. An exceeding of this value was not de-tected in the course of measuring. Please find the reports in (Annex 8). Furthermore, we installed a so-called noise sensor in the spinner area to detect possible loosen parts during operation (Annex 5). In case that a loosen part is detected, the turbine stops immedi-ately and the control system generates a fault message via SCADA system. All kinds of the mentioned measure serve as security to avoid the recurrence of such damage with such impact.



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9. Annex Annex 1:



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Annex 2:



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Annex 3

Fatigue cracks of the studs



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Annex 4:



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Annex 5



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Annex 6



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Annex 7



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Annex 8

Checking reports of remaining WEC´s

481443 481444 481445 481446 481447 481448 481449 481450 481451 481452 481453 481455 481456 481457 481458 481459 481460 481461 481462



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Annex 9



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2009-02-02 S-02872-012 Final Report -...

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