ABSTRACT
Outdoors, moisture as rain, drizzle or in another form in combination with environmental pollution causes electrical discharges on polymer insulation that result in degradation in the form of electrical tracking and erosion. Even indoors, it is possible that this degradation can occur, although the phenomena take a longer time to evolve. In such cases, degradation is detrimental to the life of the insulation. In order to make the insulation more resistant to these discharges, inorganic fillers are added to polymeric materials which, at the same time, reduces material costs. Indeed, there are more than twenty reasons for including fillers in a polymer matrix. Microfillers have been used widely to modify physical properties and, consequently, the effects of this on the properties of the resultant composite are well known. However, in recent times, nanofillers are being
used increasingly in some formulations, in order to improve both mechanical and electrical properties. The main problem in using nanofillers is that the nanoparticles agglomerate easily, because of their high surface energy, such that conventional mixing techniques are unable to achieve effective dispersion. A secondary problem is the incompatibility of the hydrophobic polymer with the hydrophilic nanoparticles, which results in poor interfacial interactions. Nevertheless, if the nanoparticles are well dispersed, the electrical properties of these materials will be significantly improved.To improve nanoparticle dispersion, several techniques are available apart from mixing, which include surface modification of the nanoparticles by chemical and physical methods through the use of surfactants.To evaluate the erosion resistance of nanocomposites, several test methods, including laser ablation, corona resistance, arcing resistance, salt fog, and inclined plane tests are used. An example included in this chapter confirms that combinations of microfiller and nanofiller with a surfactant results in composites with improved erosion resistance to dry band arcing. In order to understand this mechanism, fumed nanosilica, natural nanosilica, and nano alumina were introduced into a silicone rubber (SiR) matrix and the thermally decomposed silicone and the residual char that is formed during laser ablation tests were examined. The formation of a continuous layer on the surface behaves as a thermal insulator, protecting the material underneath from further decomposition. 10.1 The Surface Erosion Issue in Insulation
SystemsIn general, any conductor at a high voltage requires electrical insulation and in all such applications, insulating properties must be retained up to a certain level of voltage. For example, in electrical generators and motors, the conductor used for the winding has to be insulated; in power lines it is necessary to insulate the high voltage from the ground side and, consequently, appropriate insulators are needed. However, outdoor high voltage insulation subjected to environmental factors such as any type
of moisture, UV, and pollution develops a small leakage current that can end in tracking and erosion of the surface. Usually, for high voltage silicone rubber insulators, the insulation thickness is 3 mm and over long times under polluted conditions, the leakage current can erode the complete thickness of the insulation cover (housing), as shown in Fig. 10.1. For windings in electrical machines, elevated temperatures, dust, and environmental moisture can similarly lead to erosion and tracking.
