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THE RELIABILITY OF ROTOR BLADES

Alexander Hoffmann

ENERCON Research & Development

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AGENDA

1. GENERAL REQUIREMENTS OF ROTOR BLADES FOR WIND ENERGY CONVERTERS

2. ENERCON´S STRUCTURAL DESIGN & PRODUCT PHILOSOPHY

3. MATERIAL-, COMPONENT-, AND FULL-SCALE-BLADE-TESTING

4. BLADE DE-ICING-SYSTEM

5. EROSION PROTECTION

6. LIGHTNING PROTECTION

7. TRAILING EDGE SERRATIONS (TES)

TO REDUCE TRAILING EDGE NOISE

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GENERAL REQUIREMENTS OF ROTOR BLADES

• Long-Life-Cycle, Operation up to 30 years ,

> 10^9 Load-Cycles, technical availability > 97%

• Easy and cheap design to manufacture

• Light-weight structure

• Easy transport (truck, train, ship)

• Easy and quick erection (e.g. single-blade installation)

• Low maintenance effort (e.g. high erosion-resistance)

• Low sound power level

• Lightning protection & rotor blade de-icing system

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ENERCON´S STRUCTURAL DESIGN & PRODUCT PHILOSOPHY

PEELING-STRESS

• Best possible “fail-safe” structure

• Only chamfered bonding line flanges

• For blades longer than 15m, always a double-shear-web-

design is realised

• Highest quality standards in blade productions

SHEAR-WEBS

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CENTRIFUGAL

FORCE SUPPORT

TRANSVERSE

BULKHEAD

NO-BONDING-LINE

CONTOUR WEDGE

PARTING-LINE /

NO AERODYNAMIC SHORT-CIRCUIT

ENERCON´S STRUCTURAL DESIGN & PRODUCT PHILOSOPHY

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MATERIAL-, COMPONENT- AND FULL-SCALE-BLADE-TESTING

Full-Scale-Blade-Testing static and

fatigue according to IEC 61400-23

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1. Static extreme loading in

at least four main-directions

(including Load-Safety-

Factor of approx. 135% plus

110% Test-Factor)

2. Dynamic loading in flap-

and edge direction with at

least 1 million up to 5 million

cycles and a dynamic

overloading of approx. 30%

3. Residual Strength Test

with 10% lower static

extreme loading than first

static tests

MATERIAL-, COMPONENT- AND FULL-SCALE-BLADE-TESTING

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ENERCON-Solution: Air-Blade-Heating in Rotor-Blades

DEFLECTION BOW

SHEAR-WEB DROP

BLADE DE-ICING-SYSTEM

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EROSION PROTECTION

ENERCON´S NEW EROSION PROTECTION SYSTEM:

Impact Absorption Layer consists of two layers which are bonded

together by a vulcanisation process.

a. Wear-resistant UHMWPE layer (Ultra high molecular weight

Polyethylene)

b. EPDM (Soft Rubber) layer (Ethylene Propylene Diene Monomer)

for safe connection to the fibre reinforced blade structure.

Both layers in combination provide highest resistance behaviour

against erosion.

The soft EPDM layer has a shock-absorbing effect and the outer

UHMWPE film is very resistant to erosion.

• Solution for mass production

• Retrofit solution

• Easy to repair, e.g. due to damage during transport

UHMWPE

EPDM

GFRP ROTOR BLADE

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LIGHTNING PROTECTION

LIGHTNING CURRENT PARAMETERS Symbol Unit LPL I LPL I+

Peak current I kA 200 300

Short stroke charge Qshort C 100 150

Specific energy W/R MJ/Ω 10 22,5

Time parameters of short stroke T1/T2 µs/µs 10/350

Long stroke charge Qlong C 200 1000

Time parameter of long stroke Tlong s 0,5

Flash charge Qflash C 300 1150

LIGHTNING

ATTACHMENT

POINTS

Lightning protection concept according to latest research

• Defined lightning attachment points to conduct lightning current safely to ground

• Tested according to latest standards with lightning parameters up to 5 times

higher than required for Lightning Protection Level I (LPL I, highest standardized

Lightning Protection Level)

• LPL I+ is defined by ENERCON based on LPL I with increased lightning

current parameters

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• Turbulent flow at the trailing edge

causes pressure fluctuation which

emits noise

• New geometry at the trailing edge

reduces the turbulent wake effects

• Result = Reduction of aerodynamic

noise

• Position and angle of TES directly out

of the mould for reproducible quality

TRAILING EDGE SERRATIONS (TES) TO REDUCE TRAILING EDGE NOISE

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Thank you for your attention!

ENERCON GmbH | Dreekamp 5 | D-26605 Aurich

Telefon: +49 4941 927-0 | Fax: +49 4941 927-109