Experience with model simplifications for making a large FEM calculation case computable

Today´s computing tools allow machine designers to perform powerful novel calculations. In the course of a joint research project the 3D-magnetic field within the end-winding region of a 300 MVA hydropower generator was calculated. Due to the large dimensions of the machine, complex end-portion design of the stator core and a fractional slot winding the calculation case became typically very large. Despite using most powerful FEM software the calculation could be realized only by applying appropriate simplifications and strategies for minimizing the number of finite elements. The paper describes the method for building up the 3D-FEM model of the generator and the simplifications applied. Since the quality of the calculation results is essentially determined by the simplifications incorporated into the calculation model the paper is focused on the experience with appropriate simplifications and their verification for making the case computable. Quite a few publications give the wrong impression that application of FEM methods unavoidably leads to correct results at least for large calculation cases. Quite often FEM calculation results are simply offered without disclosing the applied simplifications. However, due to our experience results become trustworthy only in case the simplifications applied are documented and justified.