High voltage transformers and cables form integral parts of the electrical power distribution network and therefore their reliable operation is crucial to preventing costly outages. A liquid dielectric, typically mineral oil, is used in transformers whilst dodecylbenzene is gradually replacing mineral oil in paper/oil cable systems. As such, the oil serves as a convenient medium for sampling to assess plant health. In the current investigation, samples of dodecylbenzene cable oil were aged at 135 ºC under conditions where the oxygen diffusion into the oil was deliberately limited. The resulting aged samples were subjected to a battery of tests to determine changes in their physical, chemical and dielectric properties. Aging resulted in yellowing, oxidation, increased water content, increased dielectric loss, increased electrical conductivity and reduced electrical breakdown strength. Copper accelerates the aging process resulting in the formation of an insoluble precipitate; however, the inclusion of this material did not affect the electrical properties of the oil indicating that it is non-polar in nature. Instead, the deterioration of the dielectric properties was found to be correlated with the production of small polar molecular compounds which remain dissolved within the oil such as water, alcohols, ketones, carboxylic acid and aldehydes.

This dataset is intended to be used in conjunction with the journal publication;"The effects of Hydration on the DC Breakdown Strength of Polyethylene Composites Employing Oxide and Nitride Fillers"Authors: I. L. Hosier, M. Praeger, A. S. Vaughan and S. G. Swinglerto be published in IEEE Transactions on Dielectrics and Electrical Insulation (accepted for publication 27th April 2017)The excel file contains the raw data used to generate each figure on a seperate tab.Abstract: Particle dispersion, water absorption/desorption and electrical breakdown behavior were studied in a range of polyethylene composites having a common matrix morphology. Three different conditioning routes (dry, ambient and wet) were used to vary the absorbed water content. Systems employing oxide fillers (silica and alumina) were found to have poor or intermediate levels of particle dispersion and could absorb/desorb significant amounts of water. Consequently, they required drying to provide breakdown strengths comparable to that of the host matrix. Systems based on calcined silica exhibited reduced water absorption and provided improved breakdown strength after ambient conditioning, despite having an identical dispersion to those utilizing untreated silica. Composites employing nitride fillers (silicon nitride and aluminum nitride) were found to have good or intermediate levels of particle dispersion. These absorbed far less water and hence provided breakdown strength values comparable to that of the host matrix following ambient conditioning. Their breakdown strength was degraded after wet conditioning with both exhibiting similar breakdown strengths despite there being a large difference in the level of particle dispersion between the two fillers. In composites based upon a hydrophobic host matrix, water absorption is largely determined by particle surface chemistry and, although the above results are presented in terms of water absorption, we suggest that changes in this characteristic can be interpreted as a proxy for changed surface chemistry. The results suggest that surface chemistry is at least as important as particle dispersion in determining the electrical breakdown strength.

This dataset should be used in conjunction with the journal publication;"The effects of water on the dielectric properties of aluminum based nanocomposites"Authors: Ian L Hosier, Matthew Praeger, Alun S. Vaughan and Steve G Swingler in: IEEE Transactions on Nanotechnology, Vol. 16, no. 4, pp. 1-10, July 2017The excel file contains the raw data used to generate each figure on a separate tab.Note: The figure ExtraTGAwork.TIF is a graphic of the effects of wet and dry conditioning on water uptake. It is mentioned in the text of the paper but there was insufficient room to include it in the manuscript.Abstract: A series of polyethylene nanocomposites was prepared utilizing aluminum nitride or alumina nano-powders with comparable morphologies. These were subsequently subjected to different conditioning regimes, namely prolonged storage in vacuum, the ambient laboratory environment or in water. The effect of filler loading and conditioning (i.e. water content) on their morphological and dielectric properties was then examined. Measurements indicated that, in the case of aluminum nitride nanocomposites, none of the conditioning regimes led to significant absorption of water and, as such, neither the dielectric properties nor the DC conductivity varied. Conversely, the alumina nanocomposites were prone to the absorption of an appreciable mass of water, which resulted in them displaying a broad dielectric relaxation, which shifted to higher frequencies, and a higher DC electrical conductivity. We ascribe these different effects to the interfacial surface chemistry present in each system and, in particular, the propensity for hydrogen bonding with water molecules diffusing through the host matrix. Technologically, the use of nanocomposites based upon systems such as aluminum nitride, in place of the commonly used metal oxides (alumina, silica, etc.), eliminates variations in dielectric properties due to absorption of environmental water without resorting to the adoption of techniques such as surface functionalization or calcination in an attempt to render nanoparticle surface chemistry hydrophobic.

This dataset is intended for use in conjuction with the publication;On the Effect of Functionalizer Chain Length and Water Content in Polyethylene/Silica Nanocomposites: Part II - Charge TransportAuthors: M. Praeger, I. L. Hosier, A. F. Holt, A. S. Vaughan and S. G. Swinglerto be published in IEEE Transactions on Dielectrics and Electrical InsulationEach page of the worksheet corresponds to a seperate figure in the paperAbstract: The effects of functionalizer chain length and water content were explored in a series of polyethylene/silica nanocomposites. Silane molecules with differing chain lengths (propyl, octyl and octadecyl) were used to vary the nanoparticle surface chemistry, while vacuum drying and water immersion were used to extract water from or add water to samples previously equilibrated under ambient conditions. Electrical conductivity was found to be highly dependent upon water content as were the space charge distributions. Both interfacial conditions and the overall charge transport through the sample were strongly dependent on absorbed water and, as such, were found to vary with time through exchange of water with the sample’s environment. Changes to charge transport dynamics due to the functionalizer chain length were, however, subtle. The removal of surface hydroxyl groups appears to be the primary mechanism by which functionalization influences electrical behavior; this reduces water uptake and, as a consequence, modifies charge transport behavior.

This dataset is intended for use in conjunction with the publication;On the Effect of Functionalizer Chain Length and Water Content in Polyethylene/Silica Nanocomposites: Part I – Dielectric Properties and Breakdown StrengthAuthors: I. L. Hosier, M. Praeger, A. F. Holt, A. S. Vaughan and S. G. Swingler which was accepted for publication in IEEE Transactions on Dielectrics and Electrical Insulation on 8th February 2017Each page of the worksheet corresponds to a seperate figure in the paperAbstract: A series of nanoparticles was prepared by functionalizing a commercial nanosilica with alkylsilanes of varying alkyl tail length, from propyl to octadecyl. By using a constant molar concentration of silane, the density of alkyl groups attached to each system should be comparable. The effect of chain length on the structure of the resulting nanosilica/polyethylene nanocomposites was examined and comparison with an unfilled reference system revealed that, other than through a weak nucleating effect, the inclusion of the nanosilica does not affect the matrix structure. Since water interacts strongly with applied electric fields, water was used as a dielectric probe in conjunction with dielectric spectroscopy to examine the effect of the nanofiller and its surface chemistry on the system. Sets of samples were prepared through equilibrating under ambient conditions, vacuum drying and water immersion. While the water content of the unfilled polymer was not greatly affected, the water content of the nanocomposites varied over a wide range as a result of water accumulation, in a range of states, at nanoparticle interfaces. The effect of water content on breakdown behavior was also explored and, in the unfilled polymer, the breakdown strength was found to depend little on exposure to water (~13% reduction). In all the nanocomposites, the increased propensity for these systems to absorb water meant that the breakdown strength was dramatically affected (>66% reduction).

A series of polyethylene-based nanocomposites was prepared, utilizing silicon nitride or silicon dioxide (silica) nano-powders, and the effect of filler loading and conditioning (i.e. water content) on their morphology and electrical properties was examined. The addition of nano-silicon nitride led to systems that were free of obvious nanoparticle aggregates, whereas the nano-silica based systems showed evidence of aggregation up to the micrometer-scale. While the nano-silicon nitride composites remained essentially dry under ambient conditions, the nano-silica-based composites absorbed appreciable quantities of water from the ambient environment, indicating that interactions with water are dependent on the nanoparticle surface chemistry. Dielectric spectroscopy showed a broad relaxation peak due to adsorbed water at nanoparticle surfaces, which shifted to higher frequencies with increased water content. Similarly, the electrical conductivity was found to be highly sensitive to the presence of absorbed water, particularly for systems containing well dispersed nanoparticles. We conclude that, in nanodielectric applications, nanoparticle surface chemistry is important in determining macroscopic properties, and not just as a means of compatibilizing the filler and the matrix. Additional factors can be critical, here, as exemplified by interactions with water.Dataset to support: Hosier, Ian et al (2016). The effects of water on the dielectric properties of silicon based nanocomposites. IEEE Transactions on Nanotechnology (TNANO).