They are caused by gear oil failures in wind turbines. They occur because no gear oil has yet been invented to withstand the extreme pressures produced within these transmissions. The latest attempt to solve this problem has seen the US Government give Dow-Corning a big grant to work on a solution – the status of the project can be seen at www.nrel.gov/wind/pdfs/day3_sessionv_3_dowcorning_jungk.pdf
It seems the solution is some years away it also shows that gear box failures are not uncommon (average one every 8 years). Even if they don’t result in spectacular fires like the one in Ardrossan in December – it is one too many.