combining the strengths of umist and the victoria university of manchester 1.1 resolving performance...

Combining the strengths of UMIST andThe Victoria University of Manchester 1.1

RESOLVING PERFORMANCE CONFLICTS IN NEW WIND TURBINE BLADE DESIGNS

ByVidyadhar Peesapati

Electrical Energy and Power Systems Group

Payam JamshidiNorthwest Composites Centre

Laith RashidMicrowave and Communication

Systems


Aim of Present Work

• To find a possible solution that answers conflicts among the following areas in wind turbine design,

1. Lightning Protection2. Radar Interference3. Material Processing and Increase In Fatigue Loading

• Groups Involved ,1. Electrical Power Systems Group (National Grid HV

Research Centre), University Of Manchester.2. The Microwave & Communications Systems Group,

University Of Manchester.3. Northwest Composites Centre, University Of

Manchester.


Issue (1) – Radar Interference

• Scatter and Ghost Targets created by large RCS of Wind Turbines.

• Scatter created by1. Tower2. Blades3. Nacelle

• Doppler signature of moving blades cause false track-initiation.

• Considerable RCS reduction on tower and nacelle can be achieved by shaping

• Blades cannot be re-shaped.• Introduction of Radar

Absorbing Material into blade is a possible solution.


Issue (2) – Lightning and Wind Turbines

• What does a lightning strike require to form?1. A tall object capable of developing streamers or leaders2. Sharp edges where the field enhancement is high.

• …Add these together, and a wind turbine, tall and its blades are the perfect set up for streamers that can attach themselves to incoming leaders.

• The blades are the most vulnerable parts to be damaged. • All new blades are now protected with an inbuilt lightning protection system.


Lightning Protection Methods


Lightning and Wind Turbines - Damage

• Not all lightning strikes end up being intercepted by the receptor or the lightning protection points. Local damage to the area around receptors is still common.

• The main mechanism of damage is when the lightning current penetrates the blade and forms an arc inside.

• The pressure/shock wave could damage the blade, or cause cracks on the surface.

(Source Global Wind Power)


Issue (3) – Fatigue

(Source DFVLR)

Stress on blades and towers induce fatigue loading : e.g. Tension-tension, torsional fatigue and tension –compression. Self weight of big blades becomes a significant issue.

RAM solution increases blades weight

Materials solutions:- Reduce weight- Use more fatigue resistant materials


Blades: Materials solution

• Needs – lightweight and high stiffness, hence composites


The Conflict of Interest….• The idea of introducing new materials into

the blade laminate causes issues for the lightning protection systems and also the blade laminate manufacturing and fatigue life.

• Efficiency of lightning protection (Attachment and Conduction).

• Introduction of new materials to the blade laminate brings forth problems such as durability and integrity of the laminate.

• Also the feasibility of adding this material in existing blade manufacturing process


Preliminary RAM Solution• Model consists of 2

additional layers to be included with the blade laminate.

• A fabricated metallic pattern of capacitors and resistors. (resonance absorbers)

• A perfect conducting sheet acting as a reflecting ground plane.

• A composite Nickel and Copper coated carbon fiber layer is tested which can be used as the reflective layer.


Materials Solution:Metal coated carbon fibres


Vacuum Infusion

Skins moulded in female moulds

Metal coated carbon veils + Epoxy resin


Lightning Impact Of RAM• Two lightning protection solutions exist – mesh and

receptor• Present model is based on the receptor lightning protection

solution (mesh solution would only work in terms of radar should a specific dielectric layer be placed above it)

• Initial model shows a significant change in the field enhancement on the down conductor (i.e. the internal blade field). This is a positive result as the chances on streamers inside the blade are minimised.

• However, the field around the receptors is significantly distorted and reduced

• Once lightning attachment has been established, the lightning protection system will have to conduct the lightning current without damage, this is tested by high current tests.


• A normal blade would show a high field intensification on the receptor.

• The field is quite high on the surface of the down conductor as well.

• The presence of a copper inner layer inside the fiber glass blade would decrease the blade internal field and, it seems, that around the receptor.

• This would decrease the inception efficiency of the receptor.• An enhanced electric field inside the fiber glass increases the risk

of breakdown of this dielectric as well.

Impact on Lightning Attachment


• All lightning current carrying components needs to conduct and dissipate the energy without causing damage

• Existing lightning protection systems rated to carry lightning current and are tested to confirm this.

• The new composite layer will have to carry part of the lightning current (IEC standards require current conduction of 200 kA).

• All conducting materials will have to be electrically bonded.

• High Current tests were performed on the new composite layer.

• Composite tested as itself and also as a sheet infused with epoxy.

Impact on Lightning Current Conduction


High Current Tests• Samples of different lengths and widths were tested.• Ideally layer should distribute strike energy evenly thus

avoiding damage to other layers.• Unfortunately it does not, even at currents levels around 15kA.

Before After


Results and Conclusions• Feasible with existing manufacturing

processes of blades.

• Affects the lightning attachment.

• Field distortion in around the receptor might be improved by selective layering.

• Present composite layer is not capable of carrying rated lightning current.


Authors• Mr Vidyadhar Peesapati• Dr Payam Jamshidi• Mr Laith Rashid• Dr Ian Cotton• Prof Paul Hogg• Prof Anthony Brown

Thanks to• Dr Alan Nesbitt (Northwest Composites)• Dr Nikolaos Kokkinos (Elemko SA, Greece)

Research has been part of the Supergen Wind Consortium funded by the EPSRC.