Enhancing Breakdown Strength of Epoxy Composites Under Polarity Reversal: Accelerated Interface Polarization by Diamond-Like Carbon Modification on Fillers

Epoxy composites face insulation challenges in DC transmission systems, primarily due to the hysteresis of interface polarization to polarity reversal. In this study, taking alumina fillers as an example, the effect of surface modification with varying sp<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>/sp<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ratios of diamond-like carbon (DLC) on the breakdown strength of the composites was investigated. The results showed that sp<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>-rich DLC modification can enhance the breakdown strength under polarity reversal from 81.2 kV/mm to 97.3 kV/mm. The polarization and depolarization current (PDC) studies showed that both the sp<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>-rich and sp<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>-rich DLC modifications accelerated all the polarization branch, decreasing their time constant to 63.0%~78.5% and 38.8%~56.5%, respectively. Further Kelvin probe force microscopy (KPFM) studies revealed that the sp<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>-rich DLC modification decreased time constants of the interface polarization from 1465 s to 955 s, which explained the enhancement of the breakdown strength under polarity reversal by charge-induced breakdown theory. This method for insulation enhancement facilitates the miniaturization of electrical equipment.