A Comparative Study of Moisture and Temperature Effect on the Frequency Dielectric Response Behaviour of Pressboard Immersed in Natural Ester and Mineral Oil

Abstract

It is important to investigate the dielectric behaviour of natural ester-paper insulation as the number of transformer choosing natural ester as its insulation oil is increasing. A comparative study of the influence of moisture and temperature on the frequency dielectric response of pressboard immersed in natural ester and mineral oil was provided. X-Y model simulation was used to indicate the difference between the frequency domain spectroscopy (FDS) characteristics of transformer main insulation system using natural ester-pressboard and mineral oil-pressboard, respectively. Compared to the mineral oil impregnated pressboard with lower moisture content, the natural ester impregnated pressboard with lower moisture content has higher E'r and tan? values in the lower frequency region at various temperatures. While there is no significant difference existing in the E'r and tan? curves of mineral oil impregnated pressboard and natural ester impregnated pressboard with higher moisture content in the lower frequency. X-Y model simulation results show that the dielectric loss difference between natural ester-paper insulation system and mineral oil-paper insulation system with the lower moisture content is more obvious at higher temperature.

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