Abstract--One possible thermal pinch point along the route of a wind farm export circuit is a J tube, commonly used to provide mechanical protection to cable sections between the sea floor and the offshore platform. Current ratings for such cable sections are not covered by the scope of IEC 60287, while the existing publications covering such systems have limitations. This paper presents an updated 2D analytical method and a 3D extension for the rating of J tubes with short air section lengths. Continuous rating comparisons have been made against a 3D finite element model which shows a 4.5% variation in rating from the 2D analytical model for air section lengths greater than 10 m, rising to 13% for short air section lengths. With the addition of longitudinal heat transfer within the new 3D analytical approach this variation decreases by 2.5%. Both methods proposed can be solved readily using conventional spreadsheet tools and are broadly compliant with the IEC 60287 methodology.Index Terms-Power cable insulation, Power transmission, Wind energy integration, Wind farms, Modelling, offshore installations.
It is considered that the present IEC 60287 standard overestimates the induced losses in SL-type armored cables, which are commonly used to connect offshore windfarms to the onshore grid. This paper addresses the issue through a series of equivalent-circuit models for the estimation of circulating-current, eddycurrent, and armor losses in these cables. Finite-element models are used for further validation. Both the finite-element and the equivalent-circuit models use an equivalent-material representation of the armor layer, for which two calculation methods are developed. The results demonstrate clearly that the equation for armor loss in such cables as presently used in IEC standards is overly conservative.
Abstract.Thermo-chemical degradation of Carbon Fibre Composite materials (CFCs) under intensive heat fluxes has been modelled. The model couples together heat diffusion, polymer pyrolysis with associated gas production and convection through partially decomposed CFCs, and changes in transport properties of the material due to the damage. The model has been verified by laser ablation experiments with controlled heat input. The numerical predictions indicate that the thermal gas transport has a minimal affect on the decomposition extent. On the other hand, the model shows that the internal gas pressure is large enough to cause fracture and delamination, and the damage extent may go far beyond the decomposition region as witnessed from experimental verification of the model.
The effects due to percolation on the bulk electrical conductivity of Carbon Fibre Composites are studied in detail. To simulate the CFCs manufacturing process the fibres are placed randomly in the polymer matrix using Monte Carlo based simulation techniques. The electric conductivity of the CFCs was then analysed using finite element modelling.
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