高压直流XLPE电缆绝缘的介电性能研究

Study on Dielectric Properties of HVDC XLPE Cables

交联聚乙烯中副产物的存在会对其绝缘性能产生影响,而脱气后的直流电缆中副产物含量分布不均匀,使绝缘性能产生差异。为了研究绝缘位置不同造成的介电性能差异,将直流电缆环切成厚度约为0.2 mm的薄膜,利用三电极电导率测试系统、直流击穿测试系统及空间电荷测试系统对绝缘内层、中层、外层进行测试。实验结果表明:3层绝缘的电导率在低温低场下没有明显差别,但在高温高场下,外层电导率值最小,内层最大;内层击穿场强最小,外层击穿场强最大,中层击穿场强与外层差别较小;在40 kV/mm场强下,内层试样在两电极附近有明显的异极性电荷积聚,中层试样内部有少量的同极性电荷积累,外层试样空间电荷分布曲线平缓。研究发现高压直流交联聚乙烯电缆内层绝缘性能最差;因此在脱气生产及性能测试中,应以内层试样作为最低要求,以确保整个绝缘都具有良好的介电性能。

The presence of by-products in cross-linked polyethylene(XLPE)affects its insulation properties,and uneven distribution of by-products for the degassed DC cable makes a difference in insulation properties.To study the difference caused by insulation positions,the HVDC cable was cut into inner specimens,middle specimens and outer specimens with a thickness of about 0.2 mm.The cable samples were tested by a three-electrode conductivity test system,a DC breakdown system and a space charge test system.The conductivity test shows that there are no obvious differences between specimens at low temperature and low electrical field.While at higher temperature and electrical field,the inner has the largest conductivity and the outer has the smallest.The breakdown test shows that the breakdown filed strength of inner samples is the lowest while the outer largest and there is a little difference between the middle and the outer.From the space charge test,the obvious heteropolar charge accumulation near the two electrodes in the inner samples and a small amount of homopolar charge accumulation inside the middle samples at 40 kV/mm are found.While the space charge distribution curve for outer samples is gentle.The inner specimens have the worst dielectric properties.Therefore,in the degassing production and performance tests,it is suggested to take the inner insulation as the minimum requirement to ensure good performance for the entire cable insulation.