Electro-Thermal Aging Characteristics and Dielectric Properties of Silicone Rubber for High Voltage Applications

Silicone rubber is extensively employed in power equipment, due to its excellent temperature resistance, elasticity and electrical insulation properties. However, long-term electrothermal coupling stress is prone to trigger the degradation of its molecular chain, leading to the deterioration of macroscopic properties. This paper systematically shows the performance evolution law of silicone rubber under the effect of electrothermal aging, and reveal the correlation between microstructure and performance. The accelerated aging tests were conducted under coupled electro-thermal stresses, with temperatures set at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$120^{\circ} \mathrm{C}, 150^{\circ} \mathrm{C}$</tex>, and 180° C combined with electric fields of 6,10, and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$14 \text{kV} / \text{mm}$</tex>, respectively. The results show that under low electric field, the aging of silicone rubber is dominated by thermal mechanism. In the early stage of aging, thermal degradation induces the rearrangement of molecular chains and the slight improvement of dielectric properties. Under high electric field, the electric-thermal synergistic effect is significant. The breakdown strength decreases from 25.69 <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{kV} / \text{mm}$</tex> to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$24.69 \text{kV} / \text{mm}, 23.51 \text{kV} / \text{mm}$</tex>, at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$120{ }^{\circ} \mathrm{C}, 150{ }^{\circ} \mathrm{C}$</tex> respectively. This study elucidates the molecular structure evolution of silicone rubber under the action of electric field and heat and the dielectric properties correlation mechanism.