Within the research, mathematical models were developed to evaluate the thermal state of the insulation system in the rods of the stator winding and for a comparative analysis of thermophysical effects on the state of structural elements of the insulation system at the slot part, frontal part of the stator winding and at the zone of winding exit from the slot. The authors analyze the obtained experimental data and the mathematical modeling results of thermophysical processes for the insulation structure implemented using Global VPI and Resin Rich technologies as applied to the air-cooled turbine generator with output of 225 MW. In light of the fact, the standard thermal control system does not provide information about the average and maximum temperature drops across the insulation thickness, the maximum copper temperature of the stator winding rods, the average temperature on the insulation surface, the calculated identification of loaded critical zones in the elements of the insulation structure is a vital task in the design of turbine generators. Adopting sound design decisions minimizes local overheating and increases the insulation system reliability.