Curing kinetics and residual stress modelling of gas-insulated transmission lines tri-post insulators

Abstract

The tri-post insulator is a core component within the gas-insulated transmission lines (GIL), providing both electrical insulation and mechanical support. Typically, it is high-temperature cured through vacuum casting of a mixture of epoxy resin, curing agent, and alumina fillers. In recent years, frequent incidents of mechanical cracking and breakdown of tri-post insulators have been reported, which are attributed to residual stress concentration. However, the formation mechanism and distribution characteristics of the residual stress remain unclear. This study focuses on the curing kinetics and residual stress modelling of GIL tri-post insulators. It is verified that the epoxy resin/alumina reaction system follows the autocatalytic curing kinetic model by differential scanning calorimetry tests, and the model fitted by Malek's method corresponds well with the experimental results. Based on the Cure Hardening Instantaneously Linear Elastic model and the density inhomogeneity, it is found that a tensile stress concentration with a maximum value of 58.9 MPa at the edge of the insulator/sleeve interface, due to the mismatch of chemical and thermal shrinkage effects. Besides, the filler sedimentation can decrease the coefficient of thermal expansion and suppress the residual stress concentration. The investigation would help with the visualisation of the residual stress distribution in GIL tri-post insulators and provide some guidance for their processing treatments.