Optimal Insulation Thickness Design for Partial Discharge-Free Operation in Automotive and Aerospace Electrical Machines

This paper presents a novel continuum methodology for optimizing turn-to-turn insulation thickness (IT) in electrical machines, ensuring partial discharge-free operation (PDFO) while maximizing efficiency. Grounded in Schumann's streamer inception criterion, the approach integrates enhancement factors (EFs) from IEC 60034-18-41, including thermal aging effects, to account for insulation shrinkage over a motor's lifetime. It also considers pressure variations from ground level (1000 mbar) to cruising altitude (200 mbar), facilitating easier winding manufacturing, improved cooling, reduced losses, and, consequently, higher efficiency for a fixed copper diameter and slot geometry. For automotive applications, the methodology determines the optimal IT for a 1 kV DC bus at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$20^{\mathrm{o}}\mathrm{C}, 120^{\mathrm{o}}\mathrm{C}$</tex>, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$200^{\mathrm{o}}\mathrm{C}$</tex>. In aerospace applications, it first evaluates the feasibility of PDFO for an 800 V DC bus, then identifies the maximum viable DC bus voltage and its corresponding optimal IT over the same temperature range. This framework provides a robust foundation for designing high-performance, reliable insulation systems in automotive and aerospace applications.