500 kV海缆接头绝缘恢复对XLPE工频击穿和晶相结构的影响

Effects of 500 kV Submarine Cable Factory Joint Insulation Recovery on Power Frequency Breakdown and Crystalline Morphology of XLPE

高压交联聚乙烯(crosslinked polyethylene,XLPE)绝缘海底电缆工厂接头绝缘恢复工艺对接头绝缘和近接头电缆绝缘材料的晶相结构及介电性能影响的研究,对于提升工厂接头技术具有重要意义。通过研究500 kV高压交流海缆本体、工厂接头、近接头电缆绝缘的工频击穿性能以及交联度和晶相结构的分布特征,获得了工厂接头绝缘恢复工艺对近接头电缆绝缘击穿和晶相结构的影响规律。结果表明:工厂接头和电缆本体绝缘的工频击穿场强相近,并且工厂接头绝缘的结晶度较小,内部绝缘晶体表面能较低,晶面间距较大;与电缆本体绝缘相比,近接头电缆绝缘的工频击穿场强降低,交联度增加,结晶度减小,晶体表面能降低,晶面间距增大,这可能是由于近接头电缆绝缘再加热过程而发生二次硫化所致,同时消除了近接头电缆绝缘中工厂脱气形成的热历史。因此,建议在工厂接头绝缘恢复工艺中采用降低交联温度,增长交联时间等手段保证工厂接头绝缘与电缆本体绝缘性能的一致性,同时应注意近接头电缆绝缘再加热过程的温度控制。

The effect of factory joint insulation recovery technology on the crystal morphology and dielectric properties of insulation in joint and cable near joint is of great significance to promote the factory joint technology for high voltage crosslinking polyethylene submarine cable.Therefore,we investigated the power frequency breakdown performance,crosslinking degree and distribution of crystal morphology of cable insulation of the cable bulk,factory joint and cable near joint respectively in a 500 kV high voltage AC submarine cable.The effects of factory joint insulation recovery on the breakdown and crystal morphology of cable insulation near joint were obtained.The results show that the power frequency breakdown strength of factory joint insulation is similar to that of cable bulk insulation.The factory joint insulation possesses smaller crystallinity,larger spacing of crystal plane and lower surface energy of inner insulation.Compared with cable bulk insulation,the power frequency breakdown strength of cable insulation near joint is slightly lower,the crosslinking degree slightly increases,the crystallinity reduces,and the surface energy declines,while the spacing of crystal plane increases.The reason may be that re-vulcanization occurs in the cable insulation near joint during the factory joint insulation recovery process and it may eliminate the thermal history in cable insulation near joint caused by factory degassing.Therefore,it is recommended to apply the methods of reducing crosslinking temperature and increasing crosslinking time in the factory joint insulation recovery process to ensure the consistency of insulation performance in cable bulk and the factory joint.And in the meantime,attention should be paid to the temperature control during reheating process in the cable near joint.