Evaluation of DFIG Wind Turbine Generator and Transformer Conditions with Electrical Signature Analysis

During field studies of Doubly-Fed Induction Generators (DFIG) and Singly-Fed Induction Generators (SFIG) transformer and generator failures several unusual conditions were detected. A combination of sub-synchronous control interaction, sub-synchronous torsional interaction, and starting resonances were detected with electrical signature analysis in specific operating conditions of the machines. A review of historical operating conditions, wind, thermal and power distribution system design indicate that low-level sub-synchronous resonances are present that result in unusual transformer heating/aging, generator rotor component electrical and mechanical fatigue, and gearbox wear after years of service. The severity of the condition results from a combination of average loading and distance from customer loads and wind farm configuration. In this paper we will discuss the discovery and progress in the research with potential in-service solutions to be presented.