24 June 2005
24 June 2005
A new report published by the Technical University of Denmark (DTU) in partnership with Fiberline Composites, shows how the manufacturers of glass fibre reinforced plastics (GRP) can fabricate products with high tracking resistance.
The report focuses on lightning strikes on wind turbine blades, but the findings have significance for a number of sectors using electrical insulators.
Products of glass fibre reinforced plastics (GRP) have high electrical resistance if manufactured with a homogeneous structure. This is documented by new research carried out by the Technical University of Denmark (DTU) in partnership with Fiberline Composites.
""The research shows that GRP profiles with a smooth surface and a homogeneous structure have greater tracking resistance,"" says Associate Professor Joachim Holbøll of DTU, who is one of the authors of the report.
""Accordingly, we now have scientific evidence showing how GRP manufacturers can best construct both the fibre reinforcement and also the matrix that holds the fibres. A flawless surface is particularly important to the material's tracking resistance. The surface must be free from fibres, cracks and excessive roughness,"" says Joachim Holbøll.
DTU tested a variety of GRP profiles according to IEC publication 587. The best of the profiles proved to have very high tracking resistance, less homogeneous profiles degraded more easily.
The report is based on studies carried out as part of a larger research project, and further findings are expected to be published later this year. The authors are S.F. Madsen, J. Holbøll and M. Henriksen of DTU, Elecrical Power Engineering, and N. Bjært of Fiberline Composites. The project is focused on the problems with wind turbine blades, which are growing steadily larger and thus more susceptible to lightning strike. Due to their size, wind turbine blades have to be manufactured using the manual hand-lay up method. But this production method makes it difficult to achieve a homogeneous structure and a perfect surface.
As part of the project, GRP profiles were also constructed by the pultrusion method. This technique allows the structure and surface of the material to be precisely controlled so that profiles can be custom-tailored for specific electrotechnical conditions. Among the pultruded profiles too, however, differences were found in the quality of the samples tested.
""The report's conclusions have significance not only for wind turbine blades, but also for all other applications where there are live electrical connections,"" says Niels Bjært, Technical Solutions Manager at Fiberline Composites.
”An example is the design of distribution panels, where copper busbars can be secured by means of GRP profiles. GRP is a valid alternative to standard electrical insulators as its high tracking resistance affords strong protection against short circuits,” says Niels Bjært.
The full report can be downloaded here.