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.
In the offshore wind industry, failures are often costlier than those experienced onshore. Through examination of the literature, it is clear that failures occurring in offshore transmission systems are not well documented. As a result of this, many developers and other parties involved in the planning processes associated with offshore wind farms will defer back to existing reliability metrics in the public domain. This article presents a review of European offshore wind farm transmission failures based on fusing information from multiple public domain sources. The results highlight both the spread of the reliability performance of these assets and the reliability performance over time. The results also reinforce the industry view that installation practices could lead to low reliability in the initial years of operation, resulting in increased repair costs and decreased revenue for wind farm owners and operators. The information collated in the review is also compared to metrics from across the literature to evaluate the difference in forecasted failure rates to those experienced within the industry. In general, it is found that the experienced failure rates are subject to a much higher spread in practice than those published until now.
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