Next-generation electrical machine insulation systems: Materials, processing technologies, digitalization and circular-sustainability approaches – A critical review

The electrical insulation system (EIS) is central to the reliability, efficiency, and service lifetime of electrical machines (EMs), yet it remains among the least sustainable elements of EM manufacturing. This review presents a hierarchical analysis of the EIS, spanning primary (enameled conductor coatings), secondary insulation (slot liners and electrical steel coatings), and tertiary insulation systems (impregnation and potting). Each layer is examined in terms of material composition, wet-process technologies, and processing parameters and their effects on dielectric, mechanical, and thermal performance. Advances in material formulations, impregnation and potting methods, and process automation have improved reliability and manufacturing scalability, though often at the cost of higher energy consumption and environmental impact. Identifying failure mechanisms and condition-monitoring strategies contextualizes material and process choices under real operating stresses. The review then identifies emerging pathways toward sustainable insulation, including dry insulation architectures, recyclable and low volatile-organic-compound (VoC) resins, and additive manufacturing for advanced insulation deposition. Integrating life-cycle assessment, eco-design and circular-economy principles is emphasized as essential for sustainable material selection, process design, and end-of-life management. Ultimately this review positions sustainability as a core design variable, equally as important as thermal class and dielectric strength, and a critical step toward next-generation, resource-efficient EMs.