THERMALLY-STIMULATED CURRENT AND DIELECTRIC LOSS MEASUREMENT OF POLYPROPYLENE AND TEFLON-FEP FILMS IMMERSED IN DIARYLETHANE

Some properties of oil/PP (biaxially stretched polypropylene) and oil/ FEP (Teflon FEP) composite insulators have been investigated with TSC (thermally stimulated current) techniques. The oil/PP system showed th ree TSC peaks originating from carriers captured in the swollen surfac e region of the PP. The TSC spectra depended strongly on the polarity of the poling voltage and on the impregnating temperature. Their analy sis yielded information on the carrier traps existing near the PP surf ace in the oil/PP interface region. On the other hand, the TSC spectru m of the oil/FEP system has a small impregnating temperature dependenc e and a small effect of the poling voltage polarity. The difference in TSC between oil/PP and oil/FEP systems is closely related to the diff erence in the oil-polymer interaction. The TSC is a useful method for investigating carrier traps in the surface region and their change due to the oil-polymer interaction. To investigate further the relation b etween the carrier traps and tandelta, collecting bias TSC was measure d on a specimen to which an ac voltage was applied. The results indica te that the decrease in tandelta during the ac voltage application dep ends on the amount of trapped carriers near the polymer's surface or, the decrease in carriers in the oil.