A numerical study was conducted to optimize the design of a graded corona protection system for the end-winding part of a high-power turbogenerator stator bar. Using parametric electro-thermal modeling in COMSOL Multiphysics, the influence of material nonlinearity, multi-stage architecture, coating thickness, and applied voltage level on electric field distribution and thermal loss density were analyzed. It was established that materials with nonlinear conductivity are necessary to achieve safe electric field strength levels. For high-power, high-voltage generators (≥ 26 kV), a three-stage design with a specific resistance gradient is optimal and meets technical requirements. It was found that the primary heat generation zone is located in the corona protection stage closest to the slot, and the increase in losses exhibits a significantly nonlinear dependence on voltage. An optimal coating thickness range (0.2–0.4 mm) was determined to ensure reliable operation under test overvoltages. The results provide a methodological basis for designing corona protection systems, thereby reducing the scope of full-scale tests.