3D nonlinear transient finite element analysis of eddy currents in the stator clamping system of large hydro generators

Purpose ? An accurate calculation of eddy current losses in the stator clamping parts of large hydro generators is a matter of particular interest with the initial design and the design optimization because they can reach high values and produce local thermal hot-spots due to the non-linear magnetic behaviour of the clamping plate. Design/methodology/approach ? With a fully 3D approach of the generator pole pitch, both time-harmonic and non-linear transient finite element analyses are carried out for the eddy currents using a magnetic vector potential formulation. Findings ? With the introduction of a novel modelling strategy for the non-linear clamping plate, the total eddy current losses evaluated from both analysis methods show a good agreement. Nevertheless, the time-harmonic solution in comparison with the non-linear transient solution yields different local eddy current distributions in particular with the clamping plate. Research limitations/implications ? The presented analyses use only the fundamental harmonic in the end region field. Further research will need to be carried out for the influence of the higher harmonics in the end region field and again the comparison of both analysis methods. Practical implications ? With the intention of including the numerical analyses with design review and design optimization of the generators, the results obtained from both analysis methods are compared regarding the total eddy current losses as well as their local distributions. Originality/value ? With a fully 3D approach of the generator pole pitch, second order pentahedral and hexahedral edge elements are introduced with both time-harmonic and non-linear transient eddy current finite element analyses.