Formation of Degradation Layer on Silicone Rubber Used for Insulators

Silicone rubber (SiR) insulators have been increasingly used for transmission and distribution systems. However, it is concerned that performance and property of SiR insulator in operation are degraded due to multiple stresses. We now aim to develop a diagnosis technique of degradation degree of SiR insulator exposed to the multiple stresses. In order to investigate the degradation characteristics and establish the diagnosis technique, aged specimens are required. However, it is difficult to collect a lot of aged SiR insulators used for more than several decades. Therefore, we tried to fabricate the artificial degradation surface, which is similar to ones obtained from actual fields. To analyze the surface degradation of actually aged SiR insulators, hydrophobicity class (HC) of 22kV-SiR insulators arranged for 10 and 20 years in coastal areas was first evaluated. Next, considering the multiple stresses, the degradation surface was fabricated by red clay, UV ray irradiation and surface heating. Aged SiR specimens and artificially degraded SiR spmecimens were characterized by using a contact angle meter, a scanning electron microscopy (SEM), and an attenuated total reflectance-Fourier transform infrared spectrometer (ATR-FTIR). The hydrophobicity of artificially degraded SiR specimen can be decreased due to red clay adhesion/surface pollution on its surface as the similar condition as actually aged SiR specimen. It was also found that Si-O bond, Si-CH3 bond and C-H bond can be controlled by UV irradiation and the heating temperature.