The thermal model of a turbogenerator rotor with intermediate system of ventilation worked out basing on the finite difference method is presented in the paper. It takes into account power losses generated by the main and higher harmonics of the magnetic flux density distribution in the stator-rotor gap occurring at asymmetrical short circuits as well as their various depth of penetration in the slot wedges and tooth heads. Table 1 presents the losses occurring in the 30 MW turbogenerator rotor at the asymmetrical short-circuit (the backward component of the armature current ) and the penetration depth of the losses generated at the rotor surface. The equivalent thermal diagram (Fig. 2) corresponds with the system of differential equations of heat conduction. Calculations of the temperature fields in the 30 MW turbogenerator rotor in thermal transient states after the occurrence of a short circuit have been performed by means of the developed computer program. Basing on the thermal calculation results (Figs. 3 and 4) the rules of choice of thermal protection adjustments protecting the turbogenerator rotor against the results of asymmetrical short circuits have been given.