The global economic crisis has made it impossible to timely update the electrical equipment of thermal power plants, including turbogenerators (TGs). Only their modernization is carried out. Increase of TG power is always carried out during modernization; at the same time installation and connecting dimensions should not be changed. The fulfillment of these conditions allows the usage of the old foundation and supporting systems. In the world's practice TGs with a capacity of up to 300-350 MW forgo the hydrogen cooling of the machine internal volume in favor of air cooling.

A prerequisite for such modernization (increasing power while maintaining dimensions and transition to air cooling) is to ensure sufficient heat removal from all units of the TGs due to the intensification of cooling systems and methods, [1]. All researchers note that the stator winding is the most heated element of the TG. The heating temperature depends on the mode of operation (load currents) and the conditions of heat removal; therefore, it is sufficient to have accurate data on the thermal state of this node, [1,2]. Such results can be obtained only during the TG operations. But if the results are unsatisfactory, then such a mistake will lead to a crash, which is unacceptable because of the high cost of the TG. Accurate data on the thermal state of the stator winding rods can be obtained by three-dimensional modeling of the temperature field of the stator core (core with a winding that is laid in the slots). According to the results of this simulation, we can develop proposals to improve the reliability of the TG.

The maximum load of the TG is determined by the permissible materials operating temperatures of the active parts (conductors and winding insulation, laminated steel), [3].

The program Solid Works and the finite elements method were used for the simulation, the advantage of which is rather high accuracy. The calculations were carried out for TGs that were made at the SE «Plant «Electrotyazhmash»: TGV-200 and TGV-250. Some of the data used for modeling DVT-250 is given in Table 1. To simulate the temperature distribution, not the entire stator core was considered, but one segment with a part of the winding laid into the groove.

The results of the distribution of the thermal field in the stator segments in TGV-200 and TGV-250 when cooled with hydrogen and air are presented in Fig. 1. As a result, it was found that while simultaneously increasing the power of the TG and replacing hydrogen with air, the temperature exceeded the limit value set at the plant «Electrotyazhmash» (+90 °C).

Calculations have shown that it is necessary to increase the speed of air passing through the TG from 3.7 m/s to 5.0 m/s, which is technically possible. It is also possible to revise the boundary normative value of heating, up to the permissible one at heat resistance class F (+155 °C).