Technical advantages of an nanocomposite materials for a power equipment

为了了解纳米氧化镁(MgO)/低密度聚乙烯(LDPE)纳米复合材料在电压作用下的基本电性能，对其各种性能进行了研究。主要研究结果如下：(1)与LDPE样品相比，含有氧化镁纳米填料(以下简称纳米复合材料)的样品具有更高的直流击穿强度。纳米复合材料的正电荷随平均电场的增大而增加，最高可达250kV/mm，然后随平均电场的增大而减小，直至击穿。在电场作用下，纳米复合样品中的导电电流迅速增大，空间电荷减小。纳米复合材料样品在击穿前观察到了局部加热，而LDPE样品则没有。这些结果表明，纳米氧化镁的加入提高了样品的直流击穿强度，这可能是由于空间电荷决定的传导电流的抑制作用，而不是电子雪崩的抑制作用。(2)纳米复合材料样品在交流电压下也表现出了与LDPE样品和直流电压下样品相比的优良的水树延迟和电树延迟等性能。(3)提出了一种新的利用传导电流来估算扩散系数的方法。该方法可使扩散系数的估算更加简便、实用。该方法还可用于复合绝热材料中填料分散度的估算。

To understand basic electric properties of nano-sized magnesium oxide (MgO)/low-density polyethylene (LDPE) nanocomposite under voltage application, various properties were investigated. The main results are summarized below.(1) Compared to that of the LDPE sample, the sample containing a MgO nanofiller (hereafter, called a nanocomposite) had a higher DC breakdown strength. The positive charge in nanocomposite increased as the average field increased up to 250kV/mm, and then decreased with the average field until the breakdown. The conduction current in the nanocomposite sample increased rapidly at the field bringing the decrease of the space charge. The local heating in nanocomposite sample was obverted just prior to the breakdown while their in the LDPE sample did not. From these results, The increase in the DC breakdown strength by the addition of a MgO nanofiller is probably due to the suppression effect of the conduction current determined by the space charge rather than the suppression effect of an electronic avalanche.(2) The nanocomposite sample under an AC voltage also exhibited the excellent properties such as water tree retardation and electrical treeing retardation compeered to that of the LDPE sample as well as those under a DC voltage.(3) A new method for assessing the diffusion coefficient using the conduction current was proposed. This method could bring the assessing the diffusion coefficient more easily and practically. This method also would lead to the estimation of the filler dispersion in the composite insulating materials.