冷却介质对低密度聚乙烯电树枝老化特性的影响

Influence of Cooling Medium on Electrical Tree Growing Properties of LDPE

低密度聚乙烯是电力电缆的主要绝缘材料,电树枝生长特性分析是评估电缆绝缘性能的基础。为此选用冰水、空气和硅油3种不同介质对聚乙烯进行淬火处理,采用针板电极设计出试样的电树枝生长实验系统,通过实时数字显微摄像系统对试样中电树枝生长过程进行了观测,采用差示扫描量热法分析了试样的结晶度和晶粒尺寸均匀性,采集了试样的局部放电数据并对数据进行了统计分析。试验与分析结果表明:硅油冷却聚乙烯电树枝增长速度与扩散系数均小于冰水、空气冷却试样;3种试样中,硅油冷却聚乙烯结晶度最高,晶粒尺寸分布最均匀,放电量与放电重复率较低;冰水冷却聚乙烯结晶度最低,放电量与放电重复率较高。

Low density polyethylene（LDPE） is a major type of insulation materials of power cables.Analysis of electrical tree growing properties in LDPE is the basis to evaluate insulation performances of such type of material.LDPE specimens used for electrical tree experiments were made through being cooled in ice water,air,and silicone oil.An experiment system of electrical tree growth was designed on the base of a needle-plate electrode.Electrical tree growing processes were observed by using a living microscope camera.Crystallinity and crystal grain size uniformity of LDPE specimens were analyzed through differential scanning calorimetry.Partial discharges（PDs） of specimens were measured and statistical analysis was executed to PD data.Experiment and analysis results show that growth rate and expansion coefficients of electrical trees in LDPE specimens cooled in silicone oil were smaller than those of electrical trees in LDPE specimens cooled both in ice water and in air.In the three type of LDPE specimens,the LDPE specimens cooled in silicon oil had the greatest degree of crystallinity,the most uniform size of crystal grains.The magnitudes and repetition rate of PDs in the LDPE specimens cooled in silicon oil were comparatively small.The LDPE specimens cooled in ice water had the lowest degree of crystallinity and the magnitudes and repetition rate of PDs in such specimens were comparatively great.