Thermal aging of silicone oil aromatic polyamide insulation systems

The thermal degradation behavior of silicone oil/aromatic polyamide insulation system was studied. It was found that the flash and fire points decreased due to the formation of low molecular weight by-products of such cyclic siloxane oligomers as D/sub 3/, D/sub 4/ and D/sub 5/. The gel permeation chromatography (GPC) and high performance liquid chromatography (HPLC) analysis clarified that the depolymerization of siloxane molecules happened during the thermal aging, resulting in the high- and low- molecular by-products formation. The thermal stability index (TGI) index obtained by the thermogravity (TG) measurements and cyclic oligomer detection could be used for the insulation diagnosis.