Insulating paper used in oil-filled transformer could suffer from oxidation, hydrolysis, and pyrolysis, which would cause the reduction of degree of polymerization, distortion of mechanical strength and eventually cause insulation failures. Alkoxy silane is widely used in textile and cotton products to enhance their thermal resistance and tensile strength, since alkoxy silane could form a three-dimensional film through condensation polymerization of Si-O-Si bond after hydrolysis. Inspired by this function, we try to immerse the insulating papers into three types of alkoxy silanes with different modification groups, to form thin films with specific modification group on the insulating papers, aim to enhance their insulation, mechanical and dewatering performance.
  In order to improve the anti-aging performance of insulating paper impregnated in oil-filled transformer, three kinds of silane coupling agents were selected to modify the pristine paper samples by immersing. The as-prepared sample were subsequently placed in environmental chamber with predefined temperature of 130℃ for 35 days to perform standard accelerating thermal aging experiment following IEC 62332. The specimens were periodically sampled, and the parameters of tensile strength, permittivity and breakdown voltage were regularly measured. Through the analysis of surface elements and infrared spectroscopy, it is confirmed that the alkoxy silanes could cover the surface of the insulating paper completely by the combination of hydrogen bond and cellulose cells, which protect the insulation paper from being damaged during the ageing process. In addition, the adding of amino bond could reduce the diffusion coefficient of water molecules inside the cellulose molecules, which would retard the invasions of water molecules. Amino bond would also react with water molecule ahead of cellulose molecules, which would minus the impact of water to cellulose. Consequently, the mechanical, dielectric and breakdown strength of the insulating paper would be significantly improved. All the three types of selected silane coupling agents could improve the anti-ageing performance of insulating paper. Particularly, it is noted that the insulating paper modified by (3-Aminopropyl) triethoxysilane preserved the original three-dimensional network structure of cellulose and exhibited optimal mechanical strength, dielectric properties, and breakdown strength during the whole accelerating ageing process.
 

Insulating paper,Transformer,Silane coupling agent,Thermal aging,Breakdown voltage