Electrical and Environmental Aging of Wind Turbine Generator Insulation: A Critical Review of Stress Mechanisms, Degradation, and Mitigation

Abstract

Wind turbine generators are essential components of modern renewable-energy systems, and their operational reliability is strongly dependent on the performance and durability of their electrical insulation systems. These insulation systems are continuously exposed to interacting electrical, thermal, mechanical, and environmental stresses that may progressively reduce insulation performance, reliability, and service life. The increasing application of power electronic converters introduces additional electrical stresses, particularly rapid voltage transitions, repetitive impulses, and high-frequency components, while thermal cycling, vibration, humidity, water exposure, and salinity may further accelerate insulation degradation. Therefore, understanding the combined effects of these ageing mechanisms is important for improving the reliability and maintenance of wind turbine generators, particularly in demanding offshore environments.

This study aims to critically review and integrate the principal electrical, thermal, mechanical, and environmental ageing mechanisms affecting wind turbine generator insulation. It specifically examines converter-induced electrical stress, partial discharge, thermal ageing, mechanical degradation, humidity, water exposure, salinity, and the interactions among these mechanisms. The study adopts a descriptive and critical review methodology based on the analysis and synthesis of relevant technical and scientific literature. The reviewed evidence is comparatively examined to identify major degradation pathways, condition-monitoring indicators, insulation-protection measures, testing approaches, and maintenance strategies for both onshore and offshore wind turbine applications.

The findings indicate that insulation degradation is not generally attributable to a single stress factor but results from complex interactions among multiple ageing mechanisms. Partial discharge emerges as an important diagnostic indicator, although its interpretation requires consideration of operating and environmental conditions. The findings also demonstrate the practical importance of integrating insulation design, converter control, environmental protection, condition monitoring, and maintenance planning. In real-world applications, an integrated condition-assessment approach can support earlier detection of insulation deterioration, more informed maintenance decisions, reduced unexpected downtime, and improved generator reliability and service life. The study consequently provides a consolidated framework for understanding and managing electrical and environmental ageing in wind turbine generator insulation.