| Composite insulators are widely used in power systems because of their excellent flashover resistance.Due to long-term operation in high temperature and humidity climate,in recent years,the abnormal heating failure of composite insulators in southern China has occurred frequently,which seriously threatens the safe and stable operation of power grid.Firstly,this paper studies the influence of different types of typical defects on the abnormal heating of composite insulators,and analyses the reasons for the abnormal heating.Then,the hygrothermal aging experiments of silicone ruber sheds and fiber reinforced plastic(FRP)core of composite insulators are carried out to study their hygrothermal aging characteristics and hygroscopicity characteristics.The main research contents are as follows.The temperature rise experiments of 500 kV full-size composite insulators and short-string composite insulators with artificial defects were carried out respectively.The effects of sheds cover contamination,FRP core deterioration,hygrothermal aging,interface air gap and moisture intrusion on the abnormal heating of composite insulators were systematically discussed.The results show that there are two kinds of abnormal heating modes with different characteristics and mechanisms for composite insulators.The hygrothermal aging experiments of silicone rubber sheds and FRP core of composite insulators were carried out respectively.The samples of hygrothermal aging and operation aging were analyzed by means of scanning electron microscopy,fourier transform infrared spectroscopy,thermogravimetric analysis,frequency domain dielectric spectroscopy and thermal stimulation current test.The hygrothermal aging characteristics of sheds and mandrel were studied.The results show that the hygrothermal aging can significantly accelerate the aging process of sheds and core of composite insulators.,in which the degradation of PDMS occurs mainly in the process of wet-thermal aging of silicone rubber,and the degradation degree of polydimethylsiloxane(PDMS)of samples aged for 26 days is close to that of sheds operated for 10 years,while the degradation of epoxy resin and glass fiber of core aged by hygrothermal aging and operation aging occurs.The moisture absorption characteristics of silicone rubber sheds and core materials analyzed by weighing and diffusion models.It is pointed out that the moisture absorption process of silicone rubber and mandrel conforms to Fick diffusion model.The moisture absorption and diffusion coefficients of both materials increase with the increase of the hygrothermal aging time,and are positively and negatively correlated with the environmental temperature,respectively.The research results in this paper can provide theoretical and engineering references for the operation,inspection and replacement of composite insulators in high temperature and wetland areas of southern China,and guide the research and development of composite insulators with hygrothermal aging resistance. |
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