tHigh resolution X-ray computed tomography is used to reconstruct the interior of a sample of aninsulation system based on mica-paper tapes impregnated with polyester imide resin that is used inground-wall insulation of a.c. motor – and generator – windings rated 11 kV and above. The tomographicvolume is post-processed to identify the presence of minute voids, air-bubbles and very low-densityzones that can bring-on partial discharges and material deterioration critical for the operative life of therotating machines. The tomographic volume is segmented into different materials and a computationalmesh is built on it. The electrostatic field is simulated under suitable boundary conditions at the copperconductors and at the ground side. The numerical model allows predicting the maximum intensity of theelectric field in critical zones and spotting points above the 2.2 kV/mm threshold, as derived from exper-imental partial discharge inception voltage carried out on the coil, yielding an indirect pre-evaluation ofthe insulating material that can guide the improvement of the manufacturing process (i.e. impregnationtaping).
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