Study On The Corona Aging Characteristics And Mechanism Of HTV Silicone Rubber

Composite insulators have been widely used in power system due to some distinct advantages. With the prolonging of operating time, however, some incidents have taken place on composite insulators, ulteriorly, threatened the stability and reliability of all electric lines. So the aging of composite insulators are attracting more and more interests. The corona aging characteristics and mechanism of HTV silicone rubber have been studied in this paper, which is of considerable importance to understand the anti-corona aging mechanism of composite insulators and scientifically estimate their operation life.The trap characteristics, hydrophobicity and surface states for HTV silicone rubbers aged by different factor have been investigated. The influences of corona voltage, nitric acids and relative humidity on the aging characteristics of HTV silicone rubber have been studied in details. The estimation method based on trap characteristics for corona aging of composite insulators has also been researched.The main contributions are as follows:1. The hydrophobicity of HTV silicone rubber after exposed to different voltage level or after different corona duration has been investigated. Experimental results show that when the corona discharge ceased, the silicone rubber exposed to lower voltage level for shorter duration mostly recovered its hydrophobicity, while that exposed to higher voltage level for longer duration didn't get back its hydrophobicity. Meanwhile, the hydrophobicity recovery rates varied with the corona aging processing. The little holes firstly observed on the surface of silicone rubber promote the hydrophobicity recovery; the crystal layer subsequently formed hampers it; the cracking of crystal layer accelerates the hydrophobicity recovery again; the formation of crannies makes the hydrophobicity recovery rate become slower again, further, causes the hydrophobicity loss. The above results are helpful to estimate the corona aging degree of HTV silicone rubber when combing the hydrophobicity recovery characteristics and surface states.2. The hydrophobicity of HTV silicone rubber after exposed to corona under different relative humidity has been investigated. It was revealed that when the corona duration was shorter, the hydrophobicity was affected a little. Otherwise the hydrophobicity recovery became slower with the enhancement of relative humidity, as well as the surface states changed a lot. Comparing to the results of electric particles or nitric acids, it is confirmed the cooperated effect of electric particles and nitric acids are strengthened under higher relative humidity, further, more severe aging of silicone rubber is induced.,3. The aging of HTV silicone rubber have been investigated from the aspects of trap characteristics. Experimental results show that there was some relation between the trap characteristics and surface states: when there were little holes on the surface, the TSC peak value was lower than 50pA and the trap energy level corresponded to highest current peak was lower than 0.533eV, which is called low-grade aging; when the cracks occurred, the TSC peak value was lower than 90pA and the trap energy level corresponded to highest current peak was lower than 0.680eV, this is middle-grade aging; otherwise the crannies or ditches appeared, which is called high-grade aging. From this point of view, the trap characteristics can be used as an index to qualitatively evaluate the corona aging degree of composite insulators.4. The trap characteristics and hydrophobicity of HTV silicone rubbers aged by different factor have been systematically investigated. According to the experimental results, the TSC characteristics can be correlated to hydrophobicity recovery. Under corona discharge, when the trap energy level is deepened to 0.680eV, the hydrophobicity will lose completely. In other words, the hydrophobicity loss of silicone rubber can be quantified by the trap characteristics. In this way, the trap characteristics can be used as a criterion for estimating the operating life of composite insulators.