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The thermal degradation behavior of glass fiber reinforced polymer (GFRP) in nitrogen atmosphere was studied in the present work by thermogravimetric analysis (TGA). The changes of GFRP during the thermal degradation process were characterized from both chemical composition and micro physical structure points of view by using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). The steps of thermal degradation of GFRP in nitrogen were investigated in detail by analyzing the residues at different set temperatures, then the temperature ranges for the disappearance of methyl and aliphatic structure and the appearance of carbonyl and polyaromatic structure were determined with a temperature resolution of 20 °C. The changes of micro physical structure of GFRP during the thermal degradation in nitrogen involved the softening, melt, shrinkage, appearing of twisted and shrink lines, debonding of interface between glass fiber and epoxy resin matrix and releasing the pyrolyzed gas consecutively. Based on the results, the entire process of thermal degradation of GFRP from initial intact to final deterioration in nitrogen up to 800 °C was characterized, the present work is helpful for better understanding of the thermal degradation behavior of GFRP used in high voltage composite insulator as well as in other industry applications involving the temperature rising condition.

The abnormal heating of high voltage composite insulator seriously affects the safe and stable operation of the overhead transmission line. In order to understand and avoid such accidents, the thermal degradation behavior of glass fiber reinforced polymer (GFRP) core deserves special attention. In the present work, the thermogravimetric analysis (TGA) was used to simulate the thermal degradation process of GFRP materials. The non-oxidative environment (nitrogen) and oxidative environment (air) were both used for comparing the difference of thermal degradation of GFRP in these conditions. The changes of GFRP during the thermal degradation process were characterized from both chemical composition and micro physical structure points of view by using Fourier transform infrared (FTIR) and scanning electron microscopy (SEM). By comparing the final residues of GFRP after thermal degradation in nitrogen and in air up to 800 °C, it was found that the chemical reactions during thermal degradation of GFRP contains auto-oxidation, aliphatic structure scission and formation of polyaromatic. Based on the results, the entire process of thermal degradation of GFRP from initial intact to final deterioration was characterized, the present work is helpful for better understanding of the thermal degradation behavior of GFRP used in high voltage composite insulator as well as in other industry applications involving the temperature rising condition.

Dielectric response provides an effective method to investigate the microstructure and charge dynamic of dielectrics. In the present research, the single relaxation process or conductivity process is expressed equivalently as an electrical component, in terms of micro physical structure, these electrical components can be electrically connected to form an equivalent circuit characterizing the dielectric response feature. In general there are five types of electrical components that can be inserted in an equivalent circuit: (1) a loss peak component; (2) a quasi-dc component (QDC) component; (3) a charge diffusion component; (4) a frequency independent capacitance component; and (5) a dc conductivity component. The equivalent circuit method can represent a quantitative analysis of the dielectric response, reflect the relationship between microstructure of dielectric and the measured dielectric response. The present work is helpful for understanding the Equivalent circuit and providing a theoretical analysis method of detecting the microstructure of dielectric.

The pollution on the surface of high voltage insulator including a composite insulator, ceramic insulator and glass insulator may lead to the pollution flashover of electrical outdoor insulation, thus, the characteristics of pollution on the surface of high voltage insulator deserve detail investigated. In the present work, the characteristics of saturation pollution on high voltage insulator in North China were analyzed in terms of pollution particle size analysis, pollution particle morphology and chemical component analysis. Firstly, the equivalent salt deposit density (ESDD) was measured according to the IEC 60815, the results showed that the ESDD for composite insulator was larger than the ESDD for ceramic and glass insulators. Secondly, the particle size analysis showed that the distributions of pollution particle size on ceramic and glass insulators were almost the same, however, the distribution of pollution particle size on composite insulator was quite different from the former two, more specifically, the pollution particle with lager size can be observed on the surface of composite insulator. It should be noted that due to the diffusion of LMW and the interaction between the LMW and pollution, the ESDD on composite insulator was larger and the particle size on composite insulator was alas larger than that on ceramic insulator and glass insulator, therefore, the evaluation on the pollution performance of high voltage insulator should be more comprehensive. The present study is a case study of the pollution and is helpful for better understanding of the pollution characteristics on high voltage insulator used in North China.