Mechanism of Accelerated Deterioration of High-Temperature Vulcanized Silicone Rubber under Multi-Factor Aging Tests Considering Temperature Cycling

High-temperature vulcanized silicone rubber (HTV-SR) employed for composite insulators is continuously subjected to a complex environment of alternating heat, corona discharge, humidity, etc. These stresses (especially alternating heat) complicate the aging mechanism of HTV-SR, which lacks systematic investigation. In this paper, a multi-factor aging platform considering temperature cycling, moisture, and corona discharge is established. Specifically, four temperature-cycling settings are employed, each of which lasts for 15 cycles. The surface morphology, hydrophobicity, and chemical, mechanical, and electrical properties of aged samples are methodically characterized. Experimental results show that the aging degree is correlated to the range of temperature cycling, which is attributed to diverse crosslink-degradation degrees with different temperature differences. Under a large temperature difference (70 °C), HTV-SR possesses a high crosslinking degree and a low degradation degree, making the material hard but easy to crack with alternating thermal stress. Then, severe defects and water condensation emerge on the HTV-SR surface, which promote the diffusion of corona products and water molecules into the material. The subsequent rise in crosslinking density caused by in-depth oxidation further exacerbates the aging of the material. Consequently, it brings about poor hydrophobicity, high interfacial polarization, and shallow trap energy levels in HTV-SR. This work provides a detailed analysis of the aging mechanism of HTV-SR in a simulated on-site environment.