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Influence of the air gap length on the magnetic core loss in large hydro generator

The electromagnetic modeling and simulation of existing hydro electrical generators in operation always requires a large number of variables to carry out an accurate study and to be able to properly validate the different test results. Simulation can be affected by many parameters, such as: The air gap size (the design air gap is always different from the operation air gap due to the thermal expansion) and its uniformity. In this paper, a sensitivity analysis taking into account the air gap length and the excitation current was performed. The sensitivity analysis based on finite element simulation results was performed on an existing large hydro generator of 122.6 MVA, 13.8 kV, 60 Hz, 60 poles with 504 slots, 120 rpm. The obtained results were compared to the certain measured parameters such as the air gap flux density, line current and magnetic core losses.