Evaluation of Wind Turbine Electrical and Mechanical Defects due to Nacelle Circulating Currents

Abstract— Wind turbines are critical components of renewable energy infrastructure, but they face operational challenges due to transformer, generator and powertrain defects. One cause of the defects is nacelle circulating currents. In this paper we will discuss how these currents impact generator stator insulation systems, gearbox gear and bearing, and main bearing reliability. The multiyear collaborative study included mapping circulating currents and component impacts as well as solutions attempted by OEM, owners and vendors. Generator and transformer insulation defects related to circulating currents will be identified along with gearbox and main bearing discharge currents and the source of the circulating currents and their flow. The paper will explore mitigating strategies such as improved grounding and insulating techniques for these components for both on and off-shore asynchronous wind turbines.