<p>Due to advancements in modern industry, typical high-voltage epoxy (Ep) insulation is inadequate for high temperatures and elevated voltages. To overcome this issue, Ep resin/strontium titanate (SrTiO₃) nanocomposites were synthesized to mitigate insulating flaws. Nano-SrTiO₃ was modified using the silane coupling agent KH550. The alterations in the molecular chain following the addition of modified nano-SrTiO₃ were assessed using FTIR. <i>T</i>_g confirms that Ep resin/(SrTiO₃) nanocomposites, at an appropriate filling level, reduces inter-particle distances and increase the amount of immobile Ep areas inside the nanocomposite, hence elevating the glass transition temperature. The incorporation of nano-SrTiO₃ has an obvious effect on both the dielectric constant and dielectric loss of composites. The DC breakdown strength improved with the addition of modified nano-SrTiO₃, which created deeper traps inside the bulk matrix. Furthermore, the rise in temperature leads to the creation of an electron avalanche, which diminishes charge suppression and hence reduces DC breakdown strength. The DC conductivity decreased after the addition of modified nano-SrTiO₃ into Ep resin. Moreover, the addition of modified nano-SrTiO₃ into Ep resin elevates the partial discharge initiation voltage, hence preventing discharge dispersion prior to reaching flashover. Additionally, reduced temperature significantly impacts the partial discharge inception voltage (PDIV) by lowering the kinetic energy of the charge, prolonging the de-trapping process along the surface and consequently increasing PDIV.</p> Graphical abstract <p></p>