对国产200 kV挤塑绝缘交联聚乙烯直流电缆进行切片热老化研究,通过空间电荷测试分析热老化对电缆空间电荷特性的影响.试验结果表明:未热老化试样表面靠近电极区域出现大量异极性空间电荷,导致试样内部电场发生严重畸变.这些异极性空间电荷主要源于电缆制造过程中的交联副产物,因制造过程中脱气不充分而残留在电缆绝缘内部.热老化初期,试样表面区域的异极性空间电荷快速消失,这可能是由于热老化过程中的高温加速了交联副产物的释放,降低了异极性空间电荷量,试样内部的电场畸变得到有效抑制.热老化后,试样表面区域的空间电荷由异极性电荷转变为同极性电荷,且同极性空间电荷量大致随热老化时间的增加而缓慢增加,表明XLPE材料经历了较缓慢的老化过程.
A 200kV extruded XLPE HVDC cable made in China was performed thermal ageing experi-ment, and the influence of thermal ageing on the space charge characteristics was analyzed by testing its space charge. The experimental results indicate that a large number of hetero-charges are accumulated near the surface area of the unaged sample, leading to severe field distortion of the sample. The hetero-charges mainly originate from the cross-linking byproducts of cable, which left in the insulation because of insufficient degassing during manufacturing process. In the initial stage of thermal ageing, the hetero-charges disappear suddenly. This is because the high temperature during thermal ageing process accelerates the release of cross-linking byproducts, resulting in the decrease of hetero-charges amount, making the field distortion be suppressed. When the sample is thermally-aged, the hetero-charges changes into homo-charges, and the amount of homo-charges increase slowly with the increase of thermal ageing time, which indicate that the XLPE experiences a rather slow ageing process.
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