Coming Unglued: Dielectric insulation degradation of epoxy resin under stress

Excellent insulation and mechanical properties make epoxy resin almost omnipresent in electric power systems equipment, such as transformers, circuit breakers, and insulators. But these applications can be harsh on adhesive coating, wearing down its insulative properties and posing serious hazards. “Electrical tree breakdown” — when tree-like channels form in solid insulation — is quite common and indicative of equipment insulation lifespan.

To better understand dielectric insulation degradation of epoxy resin under electrical stress, Sun et al. distinguished two types of electrostatic trees: conductive and non-conductive trees. The researchers also discovered a “pseudo-breakdown” phenomenon in non-conductive trees, whereby the tree structure physically contacts the ground electrode, yet the material temporarily retains its insulating capability.

“We wanted to understand degradation characteristics of insulating materials under various conditions to support improved electrical equipment insulation performance,” said author Hao Sun. “The two types of electrical trees we found exhibit distinct differences in morphology, growth rate, and partial discharge signal characteristics; and their impact on the insulation performance inevitably varies.”

The researchers employed a phase-field model approach to simulate development of electrical trees under varying voltages, aiming to provide a theoretical explanation from an energy perspective for the emergence of two phenomena. Results indicated that growth of electrostatic trees in epoxy resins is driven by total free energy density: conductive trees only form when electrostatic energy density exceeds a threshold; non-conductive trees form when degradation energy does not exceed that threshold.

“We hope this work encourages more research into the mechanisms of insulation degradation in materials from multiple perspectives and helps give scholars a more comprehensive understanding of material properties,” said author Xuandong Liu.

Source: “Analysis of pseudo-breakdown phenomena and phase-field simulation during epoxy resin insulation degradation,” by Hao Sun, Yifan Zhou, Dingqian Yang, Gaoyi Shang, and Xuandong Liu, Journal of Applied Physics (2025). The article can be accessed at: https://doi.org/10.1063/5.0301757 .