Residual Stress Assessment on Epoxy Insulators Using Thermo-Elastic Method

Residual stress is inevitable in epoxy insulators, which easily leads to small cracks and even insulation breakdown during the operation of GIL/GIS. This study proposes a non-destructive method to measure the residual stress on epoxy insulators using thermo-elastic effects. First, the laser-induced temperature rise of the epoxy <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Al}_{2} \mathrm{O}_{3}$</tex> composite was measured under different mechanical stresses to establish a relationship between the relative temperature rise (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta T / \Delta T_{0}$</tex>) and mechanical stress. Then, the residual stress distributions on fullsized insulator were reconstructed based on the stresstemperature relationship by scanning and measuring the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\Delta T / \Delta T_{0}$</tex> values at distributed points. The results show that the temperature rise of the epoxy <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Al}_{2} \mathrm{O}_{3}$</tex> composite is promoted by tensile stress but inhibited by compressive stress, reflecting the impacts of mechanical stress on the thermal properties of epoxy insulators. Compressive stress is present on the outer side, while tensile stress is concentrated on the inner side of basin-type insulator, with maximum values around 30 MPa. During curing, a higher temperature on the outer side of the mold leads to a faster curing rate of the insulator than the inner side. This, combined with the mismatch of thermal expansion coefficients between epoxy and aluminum, contributes to the generation of residual stress. The measurement results of residual stress are consistent with the theoretical analysis results, verifying the effectiveness of the proposed method and offering new insights into the measurement of residual stress.