On the Dielectric Properties of Liquid Silicone Rubber under Different Thermal Aging State for Dry-type Transformer

In this paper, different accelerated thermal aging test of liquid silicone rubber is designed to explore the influence of thermal aging about the insulation characteristics of liquid silicone rubber in dry-type transformers. The thermal aging mechanism of liquid silicone rubber is discussed by measuring its physical, chemical, and dielectric properties before and after aging. The results show that with the rise of aging time, the rougher the surface of liquid silicone rubber is, the larger the void is. The weight loss of silicone rubber increase with the increase of aging time. After aging, the breakdown strength of liquid silicone rubber materials first increase and then decrease. This is because silicone rubber molecules mainly undergo re-crosslinking reaction in the early stage of aging, so the number of carriers and mobility decrease. In the later aging period, the molecular chain cleavage reaction mainly occurs, which would increase the free volume and carrier mobility. Due to the above reasons, the conductivity and loss factor first decreased and then increased with the increase of thermal aging time. The polarity of silicone rubber molecules increase with the aging degree, so the dielectric constant increased. This provides a theoretical basis for the evaluation of liquid silicone rubber insulation status of drytype transformers.