Abstract
Epoxy/alumina composite materials are widely used in support insulators in air/SF6 switchgear. However, epoxy resin is difficult to be recycled or repro- cessed because of its cross-linked structure. With the worldwide promotion of net-zero strategy, it is necess- ary to investigate suitable replacement for the epoxy resin. For this purpose, this article investigates the applicability of several thermoplastic alternatives in support insulators and selects an optimal material for future research. The first study is the comparison of basic electrical and mechanical properties among several typical thermoplastics, in which the standardized material requirements for solid insulators were used as a reference. Subsequently, polycarbonate (PC), polyoxymethylene (POM), and polyamide 66 (PA66) were selected for the detailed evaluation on dielectric properties, i.e., electrical conductivity and broadband dielectric spectra (BDS). Electrical conductivity was measured in <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$- 40\,\,^{\circ }\text{C}$ </tex-math></inline-formula> to 125 °C temperature range and 1 to 8 kV/mm electric field range. BDS were tested under the identical temperature range. Results on electrical conductivity indicate that the PC has the lowest value among three studied materials, which varies slightly with electric field. An Arrhenius study was carried out to understand the variation mechanism of the conduction process. For dielectric spectra, the results of PC show little temperature dependence, whereas the other material has significantly increased dielectric loss when operating under high temperature ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$> 65~^{\circ }\text{C}$ </tex-math></inline-formula> ). The fitting results of the Havriliak–Negami (HN) model reveal the mechanism of dielectric spectra variation for the investigated thermoplastics. These results suggest that the PC has lower conductivity, lower dielectric loss, and less temperature and field dependence than the other thermoplastics, making it a potential, environmental-friendly replacement for epoxy resin in support insulators.
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