10 kV交流XLPE电缆加速热老化后交直流绝缘特性分析

Effect of thermal aging on AC and DC insulation characteristics of 10 kV AC XLPE cables

通过对比110℃加速热老化后10 kV交流交联聚乙烯电缆试样交直流绝缘特性的差异,采用不同温度下宽频介电谱、交直流击穿、直流电导率和空间电荷测试,结合有限元仿真,研究了不同热老化时间作用下10 kV交流XLPE电缆绝缘的交、直流电气特性,以及改为直流运行后电缆绝缘的电场分布。结果表明:随着热老化时间的延长,XLPE试样的复介电常数实部先增加后增速减慢,高频区介质损耗逐渐增加;试样的电流密度先减小后增加,空间电荷积累阈值场强则呈相反变化趋势,且试样内的空间电荷积累逐步由异极性转变为同极性。随着测试温度的增加,同一老化时间下XLPE试样的介电常数实部减小,介质损耗增加;试样的电流密度增加,阈值场强减小,试样内部空间电荷积累量有所增加,交直流击穿场强下降。直流电压下,绝缘层在靠近缆芯处电场高,电场差值随绝缘试样活化能的减小而增加。长期热老化后,电缆绝缘层的直流电场分布更均匀,且空间电荷积聚问题得到改善,有利于提升10 kV交流电缆改为直流运行的可靠性。

By comparing the AC and DC insulation characteristics of 10 kV AC cross linked polyethylene(XLPE) cable samples after accelerated thermal aging at 110 ℃, through broadband dielectric spectroscopy, AC and DC breakdown, DC conductivity, and space charge experiments at different temperatures, combined with finite element simulation, the AC and DC electrical characteristics of 10 kV AC XLPE cable insulation with different aging times, and the electric field distribution of cable insulation after changed to DC operation were studied. The results show that as the aging time increases, the real part of the complex permittivity of the XLPE sample increases first and then slows down, and the dielectric loss in the high-frequency region gradually increases. The current density of the sample first decreases and then increases, while the electric field threshold showed the opposite trend, and the space charge in the sample gradually changed from hetero-charge accumulation to homo-charge accumulation. With the increase of the test temperature, the real part of complex permittivity and the dielectric loss of the XLPE sample decreases and increases respectively. Meanwhile, the current density increases and the threshold field decreases, and the amount of space charge accumulation has increased. In this way, the AC and DC breakdown field strength decreases. Under DC voltage, the insulation layer has a higher electric field near the cable core, and the electric field difference increases as the decrease of the activation energy of the insulation samples. After long-term thermal ageing, the DC electric field of the cable insulation is more uniformly distributed and the problem of space charge accumulation is ameliorated, which contributes to the reliability of the 10 kV AC cable under DC operation.