Investigation of the surface microstructure evolution of silicone rubber during corona discharge via slow positron beam and electrochemical impedance spectroscopy

Abstract

Silicone rubber is the outer dielectric material of the composite insulator used in high‐voltage transmission lines. A study of the microstructure evolution during corona discharge could provide a new understanding of catastrophic fracture in composite insulators. In this paper, the corona degradation process of silicone rubber is divided into three stages based on the data obtained by slow positron beam and electrochemical impedance spectroscopy. In stage I, the S parameter decreases slightly in the low‐energy range, suggesting a crosslinking process in the polymeric “skin,” and the silicone rubber holds its high value of resistance, Rpore. In stage II, the organic sample surface is gradually transformed into an inorganic one. Further cracking of the surface layer contributes to a dramatic increase in the sample porosity. At the beginning of water immersion, the Bode phase angle remains approximately goodbreakinfix−50∘ at low frequency, and a diffusion‐dependent Warburg impedance is observed. In stage III, a massive number of polar groups and inorganic particles are generated and the sample fails to repel water. The increase in the sample porosity is the main factor that leads to an ingress of water and failure of the material, while the generated polar groups are the secondary factor.

Effect of aluminum hydroxide (ATH) content on free volumes and water barrier property of silicone rubber

“…The corona equipment used a needle plate electrode, and the entire unit was placed in an environment with a temperature of 23 • C and a relative humidity of 45 % RH. Then, each sample was submitted to corona discharge at 10 kV for 48 h. For further details on the sample preparation and corona instrument can be found in our previous works [22,23].…”

Review of the Performance of High-Voltage Composite Insulators

“…The silica layer so formed impacts the porosity of the material, affecting moisture absorption, which is considered as the main factor contributing to material failure due to corona discharges [ 78 ]. The increased porosity which helps the moisture ingress into silicone rubber by providing diffusion pathways also contributes in reducing its hydrophobic performance [ 79 ]. Zhang and co-workers [ 80 ] presented results indicating that the saturated water absorption ratio and the relative content of Si and O elements are significantly correlated with operating time.…”

Influence of Crosslinking Extent on Free Volumes of Silicone Rubber and Water Diffusion after Corona Discharge

“…The adding of ATH particles improves the thermal conductivity and fire retardance of silicone rubber which can enhance thermal stability [ 21 , 22 , 23 ]. Wang et al investigated the influence of corona discharge time and different inorganic filler contents on the water repellency of silicone rubber [ 24 , 25 ]. In conclusion, current studies have focused on the influence of inorganic fillers to the water repellency of silicone rubber.…”