The Cork Harbour 220kV Submarine Cable Project

摘要

One of the first 220kV AC XLPE insulated submarine cable projects in the world has been completed by the Electricity Supply Board (ESB) in 2011 in Cork, Ireland. The Aghada – Raffeen circuit, which comprises 3.3km of submarine cable and 3.5km of underground cable, was installed in 2010. The Glanagow – Raffeen circuit, which comprises 4.6km of submarine cable and 7.4km of underground cable, was installed in 2011. Both submarine cables were connected to underground cables at the shore landing points. The two circuits connect a total of 876MW of generating capacity from two new generating plants at Aghada and Whitegate to the Irish transmission grid. The paper describes the project from the route selection stage through to final testing and outlines the challenges that were overcome in the project. The route selection process involved carrying out a detailed hydrographical and geophysical survey, sea bed bathymetry, locating existing cables and obstacles, side-scan sonar and sub-bottom profiling, core sampling and a study of marine archaeology. Route selection also involved consultation with key stakeholders including the Port of Cork and local fishing interests. An environmental report was prepared and a foreshore licence was obtained from the Irish Government. The submarine cables for each circuit were produced in single continuous manufacturing lengths, as no factory joints or field joints were allowed due to limited service experience at this time. Following factory testing, the cables were transported to Ireland for installation. Four cables were laid for each circuit, including a spare phase. Prior to cable laying, the shore end landing points and near shore trenches were prepared. The cables were laid in shallow conditions where water depths were generally no more than 6 metres at high tide. This meant that highly customised cable installation methodologies had to be developed, taking into account cable laying vessel positioning, water depths, tides, currents, daylight and foreshore licence conditions. Both submarine cable routes involved crossings of deeper channels over short distances; the Glanagow – Raffeen circuit crosses the main shipping channel and this crossing had to be done while maintaining access for shipping during cable laying operations. Following cable laying, they were protected by embedding to a depth of 1 to 2 metres using high pressure water jetting. The cable design for the submarine cables had to take into account the mechanical, electrical and thermal elements and it was necessary to ensure that the required rating of the circuit was met at all points along the circuit, particularly on the approach of the submarine cable to the transition joint. The underground and submarine cables were jointed together at the shore end landing points which were then reinstated to their original condition. A post lay survey was carried out to confirm the position and burial depth of the cables. The commissioning of the cable circuits included a high voltage AC test with an applied voltage of 1.4U0 using a mobile resonant test set.