Technical advantages of an nanocomposite materials for a power equipment

为了解纳米氧化镁（MgO）/低密度聚乙烯（LDPE）纳米复合材料在电压作用下的基本电学性能，研究了其各种性能。主要结果概述如下。(1)与LDPE样品相比，含有MgO纳米填料（以下称为纳米复合材料）的样品具有更高的直流击穿强度。纳米复合材料中的正电荷随着平均电场的增加而增加，直到250 kV/mm，然后随着平均电场的增加而减少，直到击穿。在电场作用下，纳米复合材料样品的导电电流迅速增加，空间电荷减少。纳米复合材料样品中的局部加热刚好在击穿之前出现，而LDPE样品中的局部加热则没有。从这些结果来看，通过添加MgO纳米填料而增加的DC击穿强度可能是由于由空间电荷决定的传导电流的抑制效果，而不是电子雪崩的抑制效果。(2)在交流电压下的纳米复合材料样品也表现出优异的性能，如水树延迟和电树延迟相媲美的LDPE样品，以及在直流电压下。(3)提出了一种利用传导电流估算扩散系数的新方法。该方法使扩散系数的计算更加简便、实用。该方法也将导致在复合绝缘材料中的填料分散的估计。

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.