Effect of Combining Nano- and Microfillers for the Assessment of Thermal Class of Glass Fiber-Reinforced Epoxy Composites for Outdoor Insulation

The present work was taken up with the objective to develop a compact and reliable hybrid composite insulation, investigate the thermal properties of the developed composites, and correlate the experimental data with the results of mathematical modeling. A composite material made of unidirectional glass fibers reinforced with epoxy resin and containing silica, alumina, and aluminatrihydrate fillers was fabricated using the pultrusion technique. Thermogravimetric analysis (TGA), thermal conductivity, and coefficient of thermal expansion (CTE) were conducted on the developed composites. The energy of activation was estimated from the thermograms using mathematical models to assess the thermal class of the composites. Though the G-E composite is typically classified under class-F insulation, the study has established that the unique filler combination has a higher temperature index ranging between 156 °C and 166 °C. The improvement in thermal performance was observed when each filler is present in a weight percentage of 10%. The hybrid composites have excellent thermal conductivity (0.43 W/mK), a low CTE (
$22.1~\mu \text {m}/\text {m}\cdot ^{\circ }\text{C}$
), and hence useful for high-temperature insulation applications such as circuit breakers, vacuum interrupters, transformers, and switching gears.