预交联对XLPE直流电缆料空间电荷特性的影响

Effect of Pre-crosslinking on Space Charge Characteristics of XLPE DC Cable Materials

在交联聚乙烯(XLPE)电缆料的挤出过程中,当局部挤出温度高于交联剂的分解温度时,交联剂会提前热分解,从而导致材料发生低程度的预交联。为研究预交联对XLPE直流电缆料空间电荷特性的影响,本文在对XLPE直流电缆料进行高温交联前,先在不同温度(140、150、160℃)下进行低程度的预交联处理。通过X射线衍射、差示扫描量热分析和交联度测试等手段表征聚集态结构,并开展不同温度下的空间电荷特性研究。结果表明:预交联会阻碍XLPE高温交联过程的正常进行,导致其交联度与结晶度均有不同程度的下降。不完善的交联结构使得预交联XLPE试样内积累了大量由电极注入的同极性电荷,同时试样内残留的较多杂质分子还会随着温度的升高解离产生大量异极性电荷,导致电场畸变严重。结晶度的下降同时还造成试样内部晶区与无定形区界面处陷阱密度和深度的增加,限制了电荷的迁移和脱陷过程。

In the extrusion process of XLPE cable materials,when the local extrusion temperature is higher than the decomposition temperature of crosslinking agent,the crosslinking agent will be thermally decomposed in advance,resulting in a low degree of pre-crosslinking in materials.To study the effect of pre-crosslinking on the space charge characteristics of XLPE DC cable materials,the low-degree pre-crosslinking treatment at different temperatures(140℃,150℃,and 160℃)was carried out before high-temperature crosslinking of XLPE DC cable materials.The aggregated structure was characterized by X-ray diffraction,differential scanning calorimetry,and crosslinking test,and the space charge characteristics at different temperatures were studied.The results show that pre-crosslinking will hinder the normal crosslinking process of XLPE at high temperature,which leads to the decrease of crosslinking degree and crystallinity.Incomplete crosslinking structure makes the pre-crosslinked XLPE samples accumulate a lot of the same polarity of charges injected by electrodes.At the same time,more impurity molecules remaining in the sample will dissociate with the increase of temperature to produce large number of the different polarity of charges,which leads to serious electric field distortion.The decrease of crystallinity also leads to the increase of trap density and depth at the interface between the crystal region and the amorphous region,which limits the charge migration and detrapping process.