Study On The Degradation Characteristics Of The Core Of Composite Insulators Under Hygrothermal Environment

In recent years,phenomena of abnormal fracture and abnormal heat occurred on composite insulators in several 500kV AC lines,which seriously threatened the operation safety of transmission lines.The corrosion of the core in the fault zone is the common feature and main cause of the abnormal fracture and partial abnormal heating of composite insulators.The core of the running composite insulator may be in the humid and hot environment which the core is very susceptible to.Therefore,it is suggested that the combined effect of damp and heat may be the inducement for the deterioration of the core of composite insulators.Accordingly,the hygrothermal aging test was carried out in the water bath environment at 50,80 and 100?.Then the aging samples were taken for appearance inspection,moisture absorption performance test,temperature rise test and physical and chemical properties test,to analyze the deterioration characteristics of core material.Finally,the comparison of the hygrothermal aging sample and the field decay core was carried out,to reveal the effect of heat and moisture on deterioration of the core rod in the field.Appearance inspection showed that the appearance of the core changed under the environment of moisture and heat,such as the color from green to brown,soft texture and pulverization of core material after dissection.Moisture absorption and temperature rise test showed that moisture absorption of the core enhanced after hygrothermal aging and temperature rise appeared on the surface of the core under 9kV voltage.With the increase of aging time and temperature,the moisture absorption and temperature rise increased.The physical and chemical properties test showed that humid and hot environment made the interface crack between epoxy resin and glass fiber,lead to the formation of pores in the core,and caused the hydrolytic reaction of the Si-O-Si bond in the glass fiber and the ester group in epoxy,which reduced the content of epoxy resin and eroded glass fiber in the core.In addition,hygrothermal aging caused occurrence of ion exchange reaction in the glass fiber,destroyed the glass fiber body,and made the glass fiber worse and broke up.In short,the core seriously deteriorated under the environment of moisture and heat,and the higher the aging temperature was,the worse the deterioration wasThe degradation characteristics of hygrothermal aging samples were in good agreement with the field core.Hygrothermal aging can simulate the decay characteristics of color yellowing and loose texture.Simulate the phenomena of'enhancement the moisture absorption and temperature rise on the core surface.Simulate the degradation of the epoxy resin of the field corrosion mandrel,the decrease of the content and the exposure of the glass fiber.Simulate the decrease of ester and Si-O-Si bonds and the increase of hydroxyl in the field corrosion core.However,the hygrothermal effect can't completely reappear the characteristics of the field corrosion core.This is because the hygrothermal aging only considered the combined effect of heat and moisture,and did not consider the role of partial discharge under high voltage.Based on the above analysis,it was known that hygrothermal environment were the important reasons for the deterioration of the core rod in the field,and played essential part in the process of decay fracture and abnormal fever of composite insulators.