Collection grid topologies for off-shore wind parks

Abstract

Offshore wind parks are expected to be a growing market for the future wind power industry. Today, some offshore wind parks are erected, especially around the coast of Denmark, and future expansions will be seen in Denmark and in the rest of northern Europe as well as in other parts of the world. The existing wind parks are in sizes up to about 200 MW, covering areas up to 20-30 km 2. The sizes of the erected wind turbine generators, WTG are about 1-2 MW and the distances between the towers are from 600-700 m almost up to 1000 m. The collection grid of an offshore wind park interconnects all the WTG, into switchgear and step-up transformers on a platform if long distances from shore or, at short distances, in a land-based switchyard. The offshore platform is then connected to the main grid on shore by subsea transmission cables. As the wind parks cover large areas, it requires a quite lot of sub-sea cable to interconnect all the WTG in a wind park. The total sub-sea cable length of a collection grid of a size of 150 MW wind park is assumed to be as much as 50 km or maybe more. This paper discusses system grounding, switching overvoltages, and reliability of supply for a number of alternative configurations of offshore collection grids. TOPOLOGIES OF COLLECTION GRIDS The circumstances, given in the previous section, have influence on the electrical system. For the feeder cables in the collection grid, which connect a number of WTG to the centrally located platform, the longest feeders will be long, CIRED2005 Session No 5

Transients in collection grids of large offshore wind parks

“…Some aspects of the design and operation of collection grids for large offshore WPs were investigated in Frankén et al 3 Otherwise, there has been very little discussion so far regarding the design of the collection grid. In the few existing offshore WPs, the grid seems to be designed as any medium-voltage (MV) underground cable system for rural/urban distribution.…”

Advanced AC and DC technologies to connect offshore wind farms into electricity transmission and distribution networks

“…In order to increase the reliability of the collection systems, single redundant 'back feed' path, single-sided ring and double-sided ring connections are proposed and investigated in Franken, Breder, Dahlgren, and Nielsen (2005) and Quinonez-Varela, Ault, Anaya-Lara, and McDonald (2007). Additional cables are used for the string connection to form a ring layout to provide redundancy for the power transfer in case of a fault without incurring excessive costs.…”

On-Shore Wind Farm Cable Network Optimisation Utilising a Multiobjective Genetic Algorithm

“…The overall unit of the failure function is cost based, but has been kept separate to the cost function in the model in order to ensure a true global optimum is found. Combining the functions can result in the algorithm not finding the true Pareto set as detailed in [1].…”

“…It is noted that although the electrical infrastructure of a wind farm, such as the cable network, is not the most expensive part of the system, it is still important to reduce its cost. This is because the electrical infrastructure comprises of roughly 10-15% of the total wind farm material costs [1], corresponding to a cost of about $ 37.5 m for a wind farm with a total cost of $ 250 m.…”