纳米粒子改性聚乙烯直流电缆绝缘材料研究(Ⅱ)

Modified Low Density Polyethylene by Nano-fills as Insulating Material of DC Cable(Ⅱ)

在电缆聚乙烯材料中添加一种新型纳米粒子可以有效改善材料中的空间电荷积聚,提高其直流击穿强度和体积电阻率。为深入了解此纳米粒子作用机理,基于电声脉冲法(PEA)和充电-放电电流法,分别测量了在不同温度下、不同纳米含量时聚乙烯纳米复合材料的极化/去极化特性。用PEA方法得到不同温度下材料的平均电荷体密度、视在迁移率和陷阱深度,结果表明,20～40°C下,纯聚乙烯及聚乙烯纳米复合材料试样内的陷阱以浅陷阱分布为主;80°C下,当聚乙烯中纳米粒子质量分数>3%时,会增加复合材料陷阱深度。用充电-放电电流法计算得到材料的迁移率,可知在20～60°C内,不同试样迁移率的变化主要由纳米粒子和温度共同作用产生,而在60～80°C内,迁移率的变化则是温度起主要作用。分析认为,电荷输运受到陷阱与温度的影响是导致电阻率变化的主要原因,而在温度梯度场下,聚乙烯纳米复合材料电阻率的正温度系数趋势是抑制材料内空间电荷积聚的主要原因。

Adding a novel nano filler in the insulation of high voltage direct current（HVDC） cable is proved to be capable of restricting space charge accumulation,and enhancing DC breakdown strength and volume resistivity of the low density polyethylene（LDPE）.In order to further study the working mechanism of the nano filler,the polarization and depolarization characteristics of pure LDPE and LDPE nanocomposites with different nano fillers under different temperatures were tested based on the pulsed electro-acoustic（PEA） method and charging /discharging current method,respectively.Parameters,including the mean volume density of space charge,apparent trap-controlled mobility and trap depth distribution,were achieved by the PEA method： shallow traps were dominant in pure LDPE and LDPE nanocomposites under 20-40°C;the trap depth increased under 80°C in nanocomposites with filler content more than 3%.Meanwhile,the carrier mobility in LDPE nanocomposites was calculated from the results of charging /discharging current method： the mobility variations were mainly attributed to both temperature variation and nano filler effect under 20-60°C,but only to temperature under 60-80°C.It is clarified from the results that the charge transportation,which is affected by trap and temperature,results in the variation of volume resistivity.Moreover,the fact that volume resistivity of LDPE nanocomposites is of positive temperature coefficient,which contributes to the restriction of space charge accumulation under temperature gradients.