GE reaches a similar conclusion when considering whether to use one transformer or two at a wind farm substation. One large substation with the same capacity rating of the wind farm is cheaper than two rated at 50% each. But the use of two stations allows savings to be made over the life of the plant -- economic optimisation needs to take into account transformer failure statistics and the impact they will have on the total energy supplied by the wind farm.
Use of cables and transformers with electrical current ratings that correspond to the rated output of the wind plant makes economic sense, even if the full capacity of the equipment is only needed for a few hours a year. So concludes a recent study by GE Energy, which supports the results of an earlier EU Funded report, European Wind Power Integration Study. Although heavy duty cables cost more than smaller cables, the energy losses will be smaller, pushing up the overall output from the wind plant. When the value of the additional electricity is aggregated over the life of the plant, it is likely to exceed the additional cost of the cables. The same logic applies to transformers. The EU report found that use of 500 kVA transformers for 300 kW machines makes sense: the initial saving in capital cost achieved by using smaller transformers is outweighed by the value of additional energy generated over the life of the plant.