A review of electrical winding failures in wind turbine generators

Since its commercial beginnings in the early 1990s, wind energy has grown to be a significant factor in the electrical generation industry, representing 9.6% of the installed capacity in Europe [1] and nearing 3.5% in North America [2]. Almost 25% of the US-based turbines are in Texas, supplying 8% of that state's annual energy requirements and peaking at almost 25% of grid demand on occasion [3]. As with any new industry, there are learning curves in nearly all aspects, but the industry is maturing and coming to terms with some of the technical shortcomings of the early generations of turbines. Although most drive train issues are related to gearbox component failures, failure of and damage to the generators are the second most common cause of lost production. As reported by George Gao and William Chen at the Electrical Insulation Conference in 2009 [4], several common failure modes have been identified, many of which can be traced to identifiable root causes. However, many failures remain difficult to trace because minor failures can lead to catastrophic electrical failures not directly related to the root cause [5]. Understanding the types of failures and how often they might occur in a fleet of turbines is instrumental to developing a proper maintenance procedure and testing regimen. By reviewing the failures of more than 1200 generators, we have been able to isolate the failures of electrical materials from the pure mechanical failures. Here, we address their occurrences and present some general suggestions for both the generator design engineers and the operating companies responsible for maintaining the wind turbine performance.