The construction of a thermal model of a fully air cooled turbine generator stator with taking into account gas dynamics is considered. The complete mathematical model includes various physical subsystems with multiphysical relationships. The study is based on accurate 3D models with the use of the modern and proven COMSOL Multiphysics software, in which the finite element method is used for calculation. The equivalent thermal conductivity of the gap between the winding bar copper conductors and stator iron is studied. The gap in question consists of the winding bar main insulation and a gap filled with additional semiconducting gaskets or similar materials. The above-mentioned physical parameter has a strong influence on the temperature distribution, because the main part of the heat releasing in the bar is transferred to the stator core through these elements. The optimal minimum equivalent thermal conductivity coefficient is analyzed and selected. A model of a turbine generator stator symmetric element together with a turbulent cooling air flow is developed and analyzed. The development of such integrated models will make it possible not only to simplify the design process, but also to analyze various insulation systems. For example, air-cooled turbine generators initially use the Global VPI insulation system; however, after replacing---for economic reasons---the stator winding, another insulation system is used, namely, the Resin Rich system. For correctly making a transition to another insulation system, integrated calculations, including thermal ones, should be carried out. In practice, after changing the insulation system, which may entail certain thermal limitations, it may be necessary to decrease the turbine generator rated power output for its further operation without overheating the stator winding, which can be obtained on the basis of simulation. In this regard, the equivalent thermal conductivity coefficient also plays an important role; its value can be preliminarily analyzed to select the necessary materials in terms of their thermal properties, and their filling factor to retain the turbine generator nominal parameters after its rewinding.
Stator Winding Second-Order Thermal Model including End-Winding Thermal Effects
