"An iron wire, 12000 feet in length, was suspended about five feet from the ground by silk cords; one end of it was connected to the globe of an electrical machine, and at the other a lead ball was hung in order to perceive when the matter reached it. After five or six turns of the wheel, the matter had passed along the whole wire and communicated its virtue to the ball, which instantly attracted and repelled light bodies. 2. As this ball was equally electrified with every part of the wire, it is probable that the electric matter would instantly pervade a wire of a still greater length, provided we had a proper apparatus for the purpose. 3. Several metals and other conductors were substituted in place of the ball, and all received the electricity in the same manner. The ball and touched with other non-conductors, :when' the finger, gave a luminous spark and as smart a shock as when the end of the wire next to 'the 'gTobe·vas touched. All these effects instantly ceased whenever .. any person not electrified touched any part of the wire and commenced again a few seconds after his hand was withdrawn. The same effects are produced, though with more difficultly, when hair or woollen ropes were substituted in place of the silk ones: But they were entirely stopped by hemp ropes or when the silk ones were wetted."

Polymeric insulators are now a common replacement for conventional porcelain and glass string insulators on overhead distribution and transmission lines. The use of this mature technology represents many advantages to the utilities; however, in polluted environments and those with high moisture levels in the environment, electrical discharges will develop on the surface of the insulation. In the long term, electrical discharges cause degradation of the polymer insulation in the form of electrical tracking and material erosion, and both are detrimental to the life of the insulation. Inorganic fillers are added to polymer materials to make the insulation more resistant to discharges, and at the same time, to lower the cost of the insulation. However, there is a limit to the amount of filler that can be added as the processability of the polymer compound becomes extremely difficult and expensive. Microfillers are extensively used to modify the physical properties of the polymeric matrix, and the properties of these composites are well known. On the other hand, nanofillers are being used in some insulating composites for reinforcement of mechanical properties; their electrical characteristics have shown inconsistency in the literature, and this is attributable to the non-uniformity of the filler dispersion. Most researchers agree that particle dispersion is critical in the development of nanocomposites for electrical insulation applications. If the nanoparticles are well dispersed, the electrical properties of these materials will be significantly improved. 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 break apart the nanoparticle aggregates. A secondary problem is the incompatibility of the hydrophobic polymer with the hydrophilic nanoparticles which results in poor interfacial interactions. In this thesis, the reinforcement of a silicone rubber matrix is successfully accomplished with the combination of microfiller, nanofiller, and a commercial surfactant. To improve particle dispersion, several techniques are available apart from mixing. This includes surface modification of the nanoparticles by chemical and physical methods by using surfactants. While surfactants are commonly applied to liquids, their use to disperse nanoparticles in compositions forming solid dielectric materials has not yet been reported. The findings in this thesis have shown that Triton X-100, a common surfactant, significantly aids in the dispersion of nanosilica and nanoalumina in silicone rubber. The main advantage of the surfactant is that it lowers the surface energy and the interfacial tension of the nanoparticles. This reduces agglomeration and facilitates the separation of the particles during mixing, thereby allowing improved dispersion of the nanofillers, as observed through Scanning Electron Microscopy (SEM). However, also shown in the thesis is that Triton X-100 cannot interact efficiently with all types of nanofillers. A high concentration of surfactant can also compromise the adsorption of the matrix polymer chains on the filler particles, so it is necessary to establish a balance between matrix adsorption and the dispersion of the particles. Mechanical properties such as the tensile strength, elongation at break, and hardness may also suffer from the use of excess surfactant. In addition, excess surfactant can lead to surface wetting properties different from composites containing none. Better wetting due to the migration of excess surfactant to the surface of the silicone may favour arcing in a wet environment. The current investigation shows that for a specific filler and concentration, an optimal concentration of surfactant provides good erosion resistance without adversely affecting the mechanical characteristics of the nanocomposite. Stress–strain and hardness measurements are done to investigate the surfactant’s effect on the mechanical properties of the composites. The effect of the surfactant on the surface of the composites is analyzed with static contact angle measurements. The heat resistance of nanofilled silicone rubber is explored using an infrared laser simulating the heat developed by dry-band arcing. Also, several industry standard test methods such as salt fog and inclined plane tests are used to evaluate the erosion resistance of the filled composites. The results of all three tests confirm that the combination of microfiller and nanofiller with surfactant results in composites with improved erosion resistance to dry band arcing, with the exception of the case where calcinated filler is used in the formulation. In this thesis, the thermal conductivity is measured using a standard ASTM method and calculated using several theoretical, semi-theoretical, and empirical models. A thermal model developed in COMSOL Multiphysics and solved using a finite element method (FEM) shows a temperature distribution in the modelled nanocomposites which is comparable to the temperature distribution measured with an infrared camera under laser heating. In addition, this investigation aims to define the mechanism by which the nanofillers improve the heat and erosion resistance of the silicone composites. In order to understand this mechanism, nano fumed silica, nano natural silica, and nano alumina are used in a silicone rubber (SiR) matrix in order to study the thermally decomposed silicone and the residual char that is formed during laser ablation tests. The white residue remaining after laser ablation on the surface of composites with fumed silica, natural silica, and alumina is analyzed in a number of ways. Scanning Electron Microscopy, Energy Dispersive X-ray analysis (EDAX), and X-ray diffraction (XRD) techniques are used to analyze the thermally decomposed silicone residue after laser heating indicating that the protective mechanism of the three analyzed nanofillers – fumed silica, natural silica, and alumina – appears to be the same. The formation of a continuous layer on the surface behaves as a thermal insulator protecting the material underneath from further decomposition.

Polymeric insulators are now a common replacement for conventional porcelain and glass string insulators on overhead distribution and transmission lines. The use of this mature technology represents many advantages to the utilities; however, in polluted environments and those with high moisture levels in the environment, electrical discharges will develop on the surface of the insulation. In the long term, electrical discharges cause degradation of the polymer insulation in the form of electrical tracking and material erosion, and both are detrimental to the life of the insulation. Inorganic fillers are added to polymer materials to make the insulation more resistant to discharges, and at the same time, to lower the cost of the insulation. However, there is a limit to the amount of filler that can be added as the processability of the polymer compound becomes extremely difficult and expensive. Microfillers are extensively used to modify the physical properties of the polymeric matrix, and the properties of these composites are well known. On the other hand, nanofillers are being used in some insulating composites for reinforcement of mechanical properties; their electrical characteristics have shown inconsistency in the literature, and this is attributable to the non-uniformity of the filler dispersion. Most researchers agree that particle dispersion is critical in the development of nanocomposites for electrical insulation applications. If the nanoparticles are well dispersed, the electrical properties of these materials will be significantly improved. 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 break apart the nanoparticle aggregates. A secondary problem is the incompatibility of the hydrophobic polymer with the hydrophilic nanoparticles which results in poor interfacial interactions. In this thesis, the reinforcement of a silicone rubber matrix is successfully accomplished with the combination of microfiller, nanofiller, and a commercial surfactant. To improve particle dispersion, several techniques are available apart from mixing. This includes surface modification of the nanoparticles by chemical and physical methods by using surfactants. While surfactants are commonly applied to liquids, their use to disperse nanoparticles in compositions forming solid dielectric materials has not yet been reported. The findings in this thesis have shown that Triton X-100, a common surfactant, significantly aids in the dispersion of nanosilica and nanoalumina in silicone rubber. The main advantage of the surfactant is that it lowers the surface energy and the interfacial tension of the nanoparticles. This reduces agglomeration and facilitates the separation of the particles during mixing, thereby allowing improved dispersion of the nanofillers, as observed through Scanning Electron Microscopy (SEM). However, also shown in the thesis is that Triton X-100 cannot interact efficiently with all types of nanofillers. A high concentration of surfactant can also compromise the adsorption of the matrix polymer chains on the filler particles, so it is necessary to establish a balance between matrix adsorption and the dispersion of the particles. Mechanical properties such as the tensile strength, elongation at break, and hardness may also suffer from the use of excess surfactant. In addition, excess surfactant can lead to surface wetting properties different from composites containing none. Better wetting due to the migration of excess surfactant to the surface of the silicone may favour arcing in a wet environment. The current investigation shows that for a specific filler and concentration, an optimal concentration of surfactant provides good erosion resistance without adversely affecting the mechanical characteristics of the nanocomposite. Stress–strain and hardness measurements are done to investigate the surfactant’s effect on the mechanical properties of the composites. The effect of the surfactant on the surface of the composites is analyzed with static contact angle measurements. The heat resistance of nanofilled silicone rubber is explored using an infrared laser simulating the heat developed by dry-band arcing. Also, several industry standard test methods such as salt fog and inclined plane tests are used to evaluate the erosion resistance of the filled composites. The results of all three tests confirm that the combination of microfiller and nanofiller with surfactant results in composites with improved erosion resistance to dry band arcing, with the exception of the case where calcinated filler is used in the formulation. In this thesis, the thermal conductivity is measured using a standard ASTM method and calculated using several theoretical, semi-theoretical, and empirical models. A thermal model developed in COMSOL Multiphysics and solved using a finite element method (FEM) shows a temperature distribution in the modelled nanocomposites which is comparable to the temperature distribution measured with an infrared camera under laser heating. In addition, this investigation aims to define the mechanism by which the nanofillers improve the heat and erosion resistance of the silicone composites. In order to understand this mechanism, nano fumed silica, nano natural silica, and nano alumina are used in a silicone rubber (SiR) matrix in order to study the thermally decomposed silicone and the residual char that is formed during laser ablation tests. The white residue remaining after laser ablation on the surface of composites with fumed silica, natural silica, and alumina is analyzed in a number of ways. Scanning Electron Microscopy, Energy Dispersive X-ray analysis (EDAX), and X-ray diffraction (XRD) techniques are used to analyze the thermally decomposed silicone residue after laser heating indicating that the protective mechanism of the three analyzed nanofillers – fumed silica, natural silica, and alumina – appears to be the same. The formation of a continuous layer on the surface behaves as a thermal insulator protecting the material underneath from further decomposition.

abstract: This thesis concerns the flashover issue of the substation insulators operating in a polluted environment. The outdoor insulation equipment used in the power delivery infrastructure encounter different types of pollutants due to varied environmental conditions. Various methods have been developed by manufacturers and researchers to mitigate the flashover problem. The application of Room Temperature Vulcanized (RTV) silicone rubber is one such favorable method as it can be applied over the already installed units. Field experience has already showed that the RTV silicone rubber coated insulators have a lower flashover probability than the uncoated insulators. The scope of this research is to quantify the improvement in the flashover performance. Artificial contamination tests were carried on station post insulators for assessing their performance. A factorial experiment design was used to model the flashover performance. The formulation included the severity of contamination and leakage distance of the insulator samples. Regression analysis was used to develop a mathematical model from the data obtained from the experiments. The main conclusion drawn from the study is that the RTV coated insulators withstood much higher levels of contamination even when the coating had lost its hydrophobicity. This improvement in flashover performance was found to be in the range of 20-40%. A much better flashover performance was observed when the coating recovered its hydrophobicity. It was also seen that the adhesion of coating was excellent even after many tests which involved substantial discharge activity. / Dissertation/Thesis / M.S. Electrical Engineering 2013

Cette thèse s’inscrit dans le cadre de l’amélioration du comportement électrique des isolateurs de lignes haute tension ; l’objectif est d’assurer une meilleure fiabilité et qualité d’alimentation en énergie électrique. Ce travail a été motivé par la nécessité de répondre à trois questions liées au comportement des isolateurs verre en zone polluée. La première porte sur la recherche d’une méthode permettant de calculer la tension de contournement des chaînes polluées selon le type d’isolateur et ses caractéristiques. La deuxième question concerne la différence de comportement entre les isolateurs en verre et les isolateurs en porcelaine de type « outerrib » ; ce type d’isolateurs présente une forme spécifique adaptée aux environnements à forte pollution. Les tensions de contournement ainsi que les trajectoires de l’arc sur les isolateurs en verre sont très différentes de celles observées avec les isolateurs en porcelaine. Et la troisième question est relative à la défaillance des isolateurs recouverts de silicone lors des essais en chocs (des impulsions de tension) à front raide. En effet, les isolateurs recouverts d’une couche de 0.3 mm (ou plus) de silicone hydrophobe explosent lorsqu’ils sont soumis à des impulsions de tension à front raide d’amplitude très élevée pendant un temps très court. Différents mécanismes pouvant être à l’origine de l’explosion/éclatement des isolateurs recouverts d’une couche de silicone sont discutés. Il ressort des différents tests et analyses que le mécanisme le plus probable semble être la fragmentation par plasma. En effet, suite à l’application d’une tension à front raide, d’amplitude très élevée, des canaux (fissures) microscopiques prennent naissance là où le champ électrique est le plus intense. L’application répétitive des chocs de tension conduit au développement de décharges dans ces canaux (rupture diélectrique de l’air) c’est-à-dire des arcs (canaux de plasma) qui se développent/propagent dans le volume de l’isolateur. La puissance déchargée (c’est-à-dire l’énergie stockée dans les condensateurs du générateur en des temps très courts) dans ces canaux à chaque choc étant très élevée, elle conduit à l’explosion de l’isolateur après quelques chocs (parfois 5 ou 6 suffisent): c’est la fragmentation par plasma. / This thesis deals with the improvement of the electrical behavior of insulators of high voltage lines; the objective is to ensure better reliability and quality of power supply. This work was motivated by the need to answer three questions related to the behavior of glass insulators in polluted areas. The first one concerns the search for method for calculating the flashover voltage of polluted chains according to the type of insulator and its characteristics. The second question concerns the difference in behavior between glass insulators and "outerrib" porcelain insulators; this type of insulator has a specific shape adapted to environments with high pollution. The flashover voltages as well as the trajectories of the arc on glass insulators are very different from those observed with porcelain insulators. And the third issue is the failure of silicon-coated insulators during shock tests (pulses) with a steep front. Indeed, insulators coated with a layer of 0.3 mm (or more) of hydrophobic silicone explode when subjected to very high amplitude steep-edge voltage pulses for a very short time. Different mechanisms that may be responsible for the explosion / puncturing of insulators covered with a layer of silicone are discussed. It appears from the various tests and analyzes that the most probable mechanism seems to be plasma fragmentation (cracking). Indeed, following the application of a steep front voltage, of very high amplitude, microscopic channels (fissures) originate where the electric field is most intense. The repetitive application of impulse voltages (shocks) leads to the development of discharges in these channels (breakdown of the air), i.e.; arcs (plasma channels) which develop / propagate in the volume of the insulator. The discharged power (i.e.; the energy stored in the capacitors of the generator in a very short times) in these channels (cracks) at each shock being very high, leads to the explosion of the insulator after some shocks (5 to 6 sometimes): it is the fragmentation by plasma or plasma cracking.