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.
We address the problem of accurately locating buried utility segments by fusing data from multiple sensors using a novel Marching-Cross-Section (MCS) algorithm. Five types of sensors are used in this work: Ground Penetrating Radar (GPR), Passive Magnetic Fields (PMF), Magnetic Gradiometer (MG), Low Frequency Electromagnetic Fields (LFEM) and Vibro-Acoustics (VA). As part of the MCS algorithm, a novel formulation of the extended Kalman Filter (EKF) is proposed for marching existing utility tracks from a scan cross-section (scs) to the next one; novel rules for initializing utilities based on hypothesized detections on the first scs and for associating predicted utility tracks with hypothesized detections in the following scss are introduced. Algorithms are proposed for generating virtual scan lines based on given hypothesized detections when different sensors do not share common scan lines, or when only the coordinates of the hypothesized detections are provided without any information of the actual survey scan lines. The performance of the proposed system is evaluated with both synthetic data and real data. The experimental results in this work demonstrate that the proposed MCS algorithm can locate multiple buried utility segments simultaneously, including both straight and curved utilities, and can separate intersecting segments. By using the probabilities of a hypothesized detection being a pipe or a cable together with its 3D coordinates, the MCS algorithm is able to discriminate a pipe and a cable close to each other. The MCS algorithm can be used for both post- and on-site processing. When it is used on site, the detected tracks on the current scs can help to determine the location and direction of the next scan line. The proposed “multi-utility multi-sensor” system has no limit to the number of buried utilities or the number of sensors, and the more sensor data used, the more buried utility segments can be detected with more accurate location and orientation.
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