Polymer dielectrics have been used as insulation for long. Many Properties have drawn researches' attention in different occasions. Generally, these topics are usually interdisciplinary while requiring necessary professional knowledge of electrical system. Potential readers may find some ideas and methods mentioned in this book hard to understand if they are not quite into the modern high voltage power system. People may want to learn some basic principles and concepts in the area of polymer insulation. To this end, this chapter provides the introduction of methods and concepts which concern with the content of this book. It is hard to be all-sided, but the introduction is sure to be helpful to understand these topics better.
TopModification Of Polymer
Modern power system is developing fast, becoming large-scaled, ultra-high voltage, distributed, flexible and hybrid. The insulation materials are now required to be multifunctional to match the operation of smart grid. Traditional materials such as silicon rubber, epoxy resin and low-density polyethylene are of great insulation, but the defects are also quite obvious, especially when the working condition or the ambient influences are quite extreme. For example, insulation in transformer usually suffers from temperature much higher than cables while super-conduction system works in cryogenic environment. Hence the insulation materials are thought to be not only insulating, but also adaptive to different external factors. However it is usually a costly and long-term project to develop a brand new material from initial study to actual use. Considering this, researchers prefer to modify traditional insulation materials instead of invented a new one from zero. The following two methods are widely applied in both industry and research. They are also included in this book.
Nanocomposite
Nanocomposite has become a very hot topic since the concept was first put forward by T. J. Lewis (1994). Nanocomposite usually consist with polymer matrix and nano-scale filler. It has been proved that nanocomposite shows better resistance to corona, electric erosion, particle discharge and breakdown. Recent researches have also presented its property of space charge and electrical treeing suppression. The ingredient of nanocomposites is quite flexible since most polymer insulation material can be applied as matrix.
The properties of nanocomposites are greatly influenced the filler. To summarize, there are three kind of filler:
In this book, different kinds of fillers are applied to achieve different function. In chapter 8, BN nano-particle is mixed with matrix to improve the thermal conductivity. In chapter 2, nano Al2O3 is used to improve the breakdown property of insulation. In occasion such as the cable accessary, space charge accumulation is a serious problem. In Figure 1, recent research has also presented the effect of nonlinear SiC particle in silicon rubber contributing to nonlinear conductivity which accelerates the dissipation of space charge (Du et al., 2016).
Figure 1. Relationship between the conductivity and the electric field
The dispersion of filler is another factor that matters. A widely used compounding method is called melt compounding. Nanocomposites in this book are most produced in this way. To examine the dispersion of filler, the scanning electron microscope (SEM) is routinely used (in Figure 2). There are also other advanced method such as transmission electron microscopy (TEM) and a Quadrat-based method put forward by Kim in 2007 (Kim et al., 2007).
Figure 2. Eaxample: SEM observation of SiR/SiC composites, (a) 10 wt%, (b) 30 wt%, (c) 50 wt%, and (d) 100 wt%