Development of a finite-element-model for transient thermal analysis of thermal cycle tests on stator bars for large rotating machines

This paper presents a three dimensional, full parameterized numerical model based on finite-element-method (FEM) to determine transient temperature distributions on real stator bar geometries. The model allows calculating the resulting timedomain thermal gradient across the insulation for internal (current) as well as external heating (oven) and therefore the comparison with measurements provided by thermal cycling tests (IEEE 1310-1990 / IEC 60034-18.34). FEM-results for simplified models of stator bar geometry are compared with the analytical results of the describing partial differential equations and advanced thermal lumped models. A detailed geometry of an exemplary generator stator bar (20 kV, 450 MVA) is modeled. This model takes several temperature depending material parameters into account. Furthermore the resulting convection, depending on cooling gas flow velocity, dynamic viscosity and temperature distribution on the stator surface, is calculated within this transient model. Finally several measurements are performed on two test-setups of generator stator bars for both situations, an internal current heating in the copper bar and external heating in an oven. The measurement and calculation results are evaluated and compared. As a result a very good correlation is obtained between theoretical and experimental investigations, which show the capability of the new developed numerical calculation model.