Condition monitoring and diagnostics of wind turbine power train

The average size of offshore wind turbines is 4.2 MW. Higher costs and installation complexity compared to onshore are the two main drawbacks that can be mainly reduced by developing larger turbines. A special case is represented by the small wind turbine world market given by turbine size less than 100 kW. At the end of 2014, the cumulative total of less than 1 million small wind turbines was installed all over the world, for a total installed capacity of about 830 MW. In terms of installed capacity, China accounts for 41 per cent of the global capacity, USA for 30 per cent and United Kingdom for 15 per cent [3]. According to the 2016s GWEC report, the growth of the whole wind energy sector will continue. At the end of the year 2020, the expected installed power will reach 800 GW globally, with an average annual installed capacity growth rate of about 6 per cent. The increase of installed capacity is also achieved by building larger and larger wind turbines up to 10 MW, able to achieve the highest wind energy harvest. Large turbines have higher failure rates and require more maintenance than small turbines. The popularity of wind energy increased the interest of companies and research centres about the technical problems related to wind turbines.