This article presents the design of a wireless power transfer (WPT)–based auxiliary power supply (APS) rated for 34-kV systems, with a primary focus on insulation design. As system voltage increases, insulation stress rises significantly, typically requiring increased conductor spacing or potting with silicone or epoxy resin, both increases APS size and weight. For a compact solution, FR4 is employed due to its high dielectric strength, enabling a lightweight, low-profile insulation with excellent repeatability. The proposed APS incorporates four WPT coil pairs connected in series to share insulation stress and reduce overall input–output coupling capacitance. The insulation design is validated through dc hi-pot testing, demonstrating a total dielectric withstand voltage of 80 kV, and partial-discharge testing with an inception voltage exceeding 48 kVrms. This performance is enabled by field-control layers, gradient layers, and optimized PCB stack selection verified through three-dimensional finite-element analysis. Experimental results demonstrate 100-W power delivery at 48-V input/output with an efficiency of 73.2% and Cio < 20 pF
