In order to study the effect of evolutions in the lamellar periodic structure of cross-linked polyethylene(XLPE)insulation for high-voltage DC cables on the DC dielectric properties under thermal aging,the thin slice samples of XLPE insulation layer of 500 kV DC cable are subjected to accelerated thermal aging at 135℃.The size of the lamellae/amorphous interphase,lamellae,and the long period of lamellae are analyzed by using small angle X-ray scattering(SAXS).The changes of DC conductance and breakdown characteristics under thermal aging are also analyzed.The experimental results show that the interphase thickness of lamellae/amorphous area,lamellar thickness and lamellar long period size increase slightly first and then gradually decrease with aging time,and the maximum value occurs when aging for 336 h,which has a similar change rule to the threshold field strength and DC breakdown strength.But it is opposite to the variation of the carrier mobility and the variation of the amorphous region size between lamellae.The effects of periodic structure of lamellae changes on DC breakdown strength are analyzed based on trap-controlled threshold field strength and free volume breakdown model.Comprehensive analysis shows that short-term thermal aging helps to improve the microcrystalline structure of XLPE,thereby improving the DC breakdown strength.
关键词
交联聚乙烯/过渡界面/片晶长周期/阈值场强/直流击穿
Key words
cross-linked polyethylene/transitional interphase/lamellar long period/threshold field intensity/DC breakdown
维普
万方数据