Degradation Monitoring of Silicone Rubber Used for Insulators

Electrical insulation equipment such as insulators contributes to reduction of electrical fault owing to overvoltage. Polymeric material such as silicone rubber (SiR) is gradually replacing porcelain. However, in Japan the application of polymeric material is limited because there are concerns about the hydrophobicity degradation and the decrease of insulation performance. Therefore, it is important to investigate not only pollution effect on the insulation performance but also the long-term reliability of polymeric material. Additionally, it is desired to establish an easy diagnostic technique which can grasp the degree of degradation of polymeric material. To evaluate the degradation degree of SiR of insulators arranged for a long period of time in the coastal area, we first characterized the surface of aged SiR specimen cut out from a line post insulator arrange for 20 years in the coastal area by using the attenuated total internal reflection Fourier transform infrared spectroscopy (ATR-FTIR). Next, we repeatedly performed a salt fog aging test against SiR specimens. Then, the surface hydrophobicity and the leakage current were evaluated. From the ATR-FTIR analysis, it was found that the reflectance peaks due to Si-CH3 symmetric bending of aged specimen decreases in comparison with those of unused specimen. The continuous salt fog aging test investigated that a required time for recovering hydrophobicity is a good index for degradation diagnosis because the required times for recovering hydrophobicity of SiR used for 20 years are much longer than that of unused SiR.