Moisture absorption characteristics of silicone rubber and its effect on dielectric properties

In a high humidity environment, the composite insulating material will absorb moisture from the air, the dielectric properties of the material may change consequently, thus accelerating degradation of mechanical and insulating properties. High-temperature vulcanized (HTV) silicone rubber, commonly used as composite insulators shed and housing materials, has been investigated for their moisture absorption characteristics and dielectric properties during the moisture absorbing process. New and operated silicone rubber materials are stored at 90% relative humidity, moisture contents and dielectric parameters are measured periodically. The diffusion coefficient and maximum moisture content of silicone rubber based on Fick´s diffusion law are calculated. Differences of water absorption and dielectric properties between silicone rubber materials before and after operating are discussed. Theoretical analysis and experimental studies have shown that moisture absorption characteristics of silicone rubber material are in good agreement with Fick´s law, and at a constant ambient humidity the diffusion coefficient and maximum moisture content of new silicone rubber are less than that of the operated. With the contents of moisture increasing, the dielectric properties of silicone rubber materials change simultaneously, and significantly differ between silicone rubber materials before and after operating. Intrusion of moisture may change the dielectric properties of silicone rubber material, and dielectric loss factor and conductivity trends exactly coincide with the moisture content. Moisture may play a crucial role in degradation of silicone rubber composite insulators, which needs further verification.