This paper deals with a high frequency model of inorganic insulated coils used to build high temperature (HT°) machine. The HT° wire has a nickel layer protecting the copper against oxidation and a thin inorganic coating with reduces insulation properties. Therefore, the coils must be designed with a special care for getting a good distribution of turn-to-turn voltage during the fast transients excited by a steep voltage increment of the PWM inverter. A specific coil structure is proposed and a high frequency (HF) equivalent circuit able to compute the turn-to-turn voltages during transients. A finite element based method for determining magnetic couplings between turns, is proposed.