Migration of vinyl acetate from semiconductive to insulation of power cables

Semiconductor compounds based on ethylene vinyl acetate (EVA) copolymers were used along with ultraclean insulation to form an ideal interface for diffusion studies. The interface was analyzed before and after diffusion at different temperatures, using micro-Fourier-transformed infrared spectroscopy. Migration of vinyl acetate species was detected at these interfaces using their characteristic absorptions at 1742, 1240, and 1025 cm/sup -1/. The results were verified for semiconductive formulations with different carbon blacks and different EVA copolymers and for actual cable samples. The diffusion profile was obtained for an ideal case by choosing an antioxidant system other than the phenolic and thio esters for the insulation. Low-molecular-weight EVA was found to migrate across the interface between the semiconductives and cross-linked polyethylene (XLPE) of power cables. A correlation is established between the tree counts and EVA detected at the interface between the conductor shield and the XLPE of a 15-kV-rated power cable.<
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