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Published at International Conference on Lightning Protection, Avignon, France, 2004 2. Description of test setup

Tracking tests of Glass fibre Reinforced Polymers (GRP) as part of improved lightning protection of wind turbine blades - 50702 Tracking tests of Glass fibre Reinforced Polymers (GRP) as part of improved lightning protection of wind turbine blades

The IEC Publication 587, “Test methods for evaluating resistance to tracking and erosion of electrical insulating materials used under severe ambient conditions” describes a test procedure where five similar specimens are tested simultaneously (Figure 1). For the present investigations the five mounting devices are produced according to the standard, except for additional banana plugs on both the high voltage electrode and the earth electrode. This allows faster replacement of test specimens (Figure 2).

S. F. Madsen

1

, J. Holboell

1

, M. Henriksen

1

, N. Bjaert

2 1: Ørsted·DTU, Electric Power Engineering, Elektrovej Building 325, DK-2800 Lyngby, Denmark 2: Fiberline Composites A/S, Nr. Bjertvej 88, DK - 6000 Kolding, Denmark Abstract : The paper describes test procedures and evaluation of the tracking resistance of several GRP specimens. Twenty one series of five specimens each have been tested according to IEC publication 587. Classification referring to the standard, as well as general comments on surface characteristics, fibre orientation, different types of resin etc. is performed. Finally some suggestions for material improvements are treated and held together with the manufacturing relations of wind turbine blades. Keywords : Tracking resistance, composite materials, wind turbine blades 1. Background Due to increasing demands for more efficient wind power generation and the availability of new manufacturing technologies, the size of wind turbines is constantly increasing worldwide. The consequence of increasing wing tip height (app. 130 m above sea level) and the trend of wind farms being placed offshore increases the probability of lightning strikes to wind turbines. The common lightning protection consists of a number of receptors and an inner down conductor inside the wing, giving some protection proven for wings of length 20m-30m. When lightning hits a wing of about 40m-50m length, the arc might either penetrate the surface and proceed towards the inner “down leader” lightning conductor, or move along the surface to the nearest receptor. The penetration is crucial and usually implies a delamination, while the arc movement along the surface may leave physical erosion referred to as tracking. An area subjected to tracking might attract further lightning because the carbonized track connected to the receptors exposes the earth potential to a larger area of the wing. It is not possible to introduce receptors that attract all lightning, so the solution must lie within the design of wing materials. The acceptance of surface discharges from point of attachment to receptor requires a thorough investigation of the materials tracking resistance. In this paper, results of the tracking resistance of different test specimens measured according to IEC publication 587 are presented and the relevance of the results for lightning protection of wind turbine wings is discussed. Figure 1: Five specimens tested simultaneously Very briefly, the test is carried out by applying a high voltage on the top electrode, while the specimen is contaminated by a flow of a saline solution. The results sketched below are all obtained by testing according to Method 2: stepwise tracking voltage and with the End