Mechanism of the Effect on Partial Discharge Characteristics of Ep/Gf Composites by Cold-To-Hot Cycling Ageing

Epoxy/glass fiber (EP/GF) composites as the main insulation support material for dry-type air-core reactors is essential for the safety and stable operation of power systems. It is well known that the insulation degradation of EP/GF composites is greatly affected by the Cold-to-hot cycling ageing caused by faults, and sudden changes in ambient temperature. However, there is still a lack of reports about the effect of cold-to-hot cycling ageing on the insulation degradation of EP/GF composites. This work was performed with thermal aging at 180° C, and some samples were subjected to cold-tohot cycling aging <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(-45^{\circ} \mathrm{C}-150^{\circ} \mathrm{C}\right)$</tex> stresses after a limited time of aging. The functional groups, morphology and insulating properties of EP/GF composites were characterized using infrared spectroscopy, ultrasonic Ascan and partial discharge test, and the effects of cold-to-hot cycling ageing on their insulation degradation were analyzed. The results show that cold-to-hot cycling ageing does not lead to changes in the functional groups of EP/GF composites, but accelerates the development of microdefects. The deeper the aging degree is, the more obvious the accelerating effect of cold-to-hot cycling ageing on the development of micro-defects is, and for EP/GF composites with 360 hours of thermal aging, the effect can even reduce the reflected wave by more than one times, which in turn makes the partial discharge strength increase dramatically.