Performance of liquid silicone rubber exposed to acid fog under DC stress

With excellent electrical properties high performance under wet and polluted conditions, wide operation temperature range and simple processing, liquid silicone rubber have been extensively used as an insulating material in power transmission and distribution system. However, in recent years, `acidic attack' is becoming a matter of concern to the reliability of silicone rubber outdoor insulation. There are indications that the root cause for the cracking or hydrophobicity loss on some silicone rubber outdoor insulation is a combination factor of electrical (corona), environmental (UV, acid rain), mechanical stresses and other effects. In order to further understand the effect factors, a new lab-scale chamber with combined acidic attack and electrical stress has been constructed. In this paper, the performance of two types of liquid silicone rubber, energized with DC 1.85 kV voltage (corresponding to a specific creepage distance of 43 mm/kV), has been tested under a 1000 h acid fog test. The leakage currents along the surfaces were continuously monitored during the 1000 h test. The hydrophobicity, surface morphology (by SEM), infrared spectroscopy and hardness of the virgin samples and samples aged after 250 h, 500 h, 750 h, and 1000 h have been evaluated. The experimental results indicated that two types of LSR rubber maintained their hydrophobic surface properties, which was also in agreement with the low leakage currents level throughout the test. For all the samples, the infrared spectra were almost unchanged during the whole 1000 h acid fog test, but the hardness increased around 20%. Moreover all the initial (before ageing) and 1000h-aged samples passed AC4.5 kV tracking and erosion tests. It was seen that LSR rubber present good performance in the acid fog environment under DC stress, no obviously indication of `acidic attack' has been observed.