电声脉冲法研究热老化对160kV直流电缆绝缘材料陷阱特性的影响

Influence of Thermal Stress on the Traps Energy Properties of 160kV HVDC Cable Insulation Material Based on Pulsed Electro-Acoustic Method

交联聚乙烯(XLPE)老化会引起内部陷阱特性的变化,进而造成空间电荷分布的变化,威胁直流电缆的安全运行。对160k V直流电缆切片进行了90℃和135℃不同程度的热老化试验,并利用电声脉冲法(PEA)探究了热老化对直流电缆空间电荷分布的影响。通过分析空间电荷的衰减规律并结合等温松弛理论,提出了利用PEA法分析绝缘材料陷阱特性的方法,并对老化前后试样内的陷阱特性进行了分析研究。研究结果表明,90℃热老化前期由于后交联反应,试样部分深陷阱转为浅陷阱,直流电缆内部空间电荷消散特性变好;但随着老化时间的进一步增加,试样内的陷阱深度及密度均有一定程度的增长,空间电荷积累量也随之增加。试样在135℃高温热老化情况下,内部发生强烈的热氧反应,结晶形态遭到严重破坏,陷阱能级及密度均大大增加。

The ageing of XLPE insulation can cause the change of trap energy properties, and further affect the distribution of space charge in the bulk of insulation. It would threaten the security of HVDC. In this paper, the slices from a 160kV DC cable were stressed at 90℃ and 135℃, respectively.The space charge distributions of the samples were measured by the pulsed electro-acoustic (PEA) method. And then the space charge decay model was established. Combined with the isothermal relaxation theory, a method to analyze the trap energy properties of the insulation materials based on the PEA method was proposed. The results showed that due to the post-crosslinking in the 90℃ thermal process, parts of the deep electron traps were converted to shallow traps, which would benefit the dissipation of the space charge. However, as the aging time further increased, the density and level of the electron traps both had a certain degree of growth, resulting in the increase of the amount of space charge. Under the 135℃ thermal stress, not only the crystalline morphology of the XLPE is greatly destroyed, but also the density and depth of the electron traps increased greatly because of the intense thermal oxidative degradation in the XLPE insulation.