Evaluation of Dielectric and Mechanical Properties of LSR Composite Under Thermal Aging

The application of liquid silicone rubber (LSR) in dry-type transformers has attracted more attention due to its high temperature resistance and recyclability. In this paper, dielectric and mechanical properties of LSR after thermal aging at 250 °C with different time of 24, 48, 96, 168 and 336 h, are investigated to evaluate the impact of thermal aging on the performance of the LSR. The experimental results reveal that the breakdown strength is reduced by 11.41% after 336 h thermal aging. The DC conductivity, loss factor and integration charge Q(t) decrease in the early stage of thermal aging (0-48 h), then begin to increase in the later stage (48-336 h), which are attributed to the competition process between the re-crosslinking and fracture reaction during thermal aging, as evidenced by the SEM and FTIR characteristics. In addition, the tensile strength and the elongation at break are decreased by 29.2% and 50% after 336 h thermal aging, respectively. Finally, the aging mechanism of the liquid silicone rubber is discussed, which could provide a theoretical basis for evaluating the insulation state of LSR under thermal aging.