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The presented paper aims to highlight the role of filler-polymer interface on the DC erosion resistance of silicone rubber (SiR) outdoor insulators. SiR composites filled with nano-sized boron nitride and fumed silica have been prepared in this study. Electrical and thermal experimental tools of the inclined plane tracking-erosion test, simultaneous thermogravimetric- differential thermal analyses, and thermal conductivity measurements are used to analyze the prepared nanocomposites. The analysis primarily investigates whether the composite’s enhancement of thermal conductivity or filler interface would be more influential on erosion suppression. Literature reports that the boron nitride filler improves SiR’s thermal conductivity, whereas fumed silica provides an exceptional interaction with SiR at the filler interface. SiR was filled with boron nitride at 5wt% (percent by weight) and 10wt%, while fumed silica was loaded with 5wt% and used as a reference composite in the study. The obtained results clearly indicate a superior erosion resistance of the silica filled SiR over the boron nitride filled one. An observation which seemingly could give more significant role of the filler-polymer interface on the erosion resistance of SiR used for high voltage DC outdoor insulators., IEEE 2020 International Conference on Dielectrics, 6-31 July, Virtual Edition, Valencia, Spain

This paper investigates the erosion suppression effects of the water of hydration in alumina tri-hydrate and magnesium hydroxide fillers in silicone rubber during the AC and DC dry-bad arcing. Simultaneous thermogravimetric and differential thermal analyses show the hydrated filler type, level and size affecting erosion. Water of hydration in alumina tri-hydrate is shown to be released before the depolymerization of silicone rubber; whereas, the water of hydration in magnesium hydroxide is released during the depolymerization. As such, alumina tri-hydrate could promote a stronger shield of residue against dry-band arcing as compared to magnesium hydroxide, which could further suppress erosion. Increasing the hydrated filler loading raises the amount of the water of hydration released, which could dilute the silicone rubber in the gas phase and suppress combustion. However, insignificant effect on the suppression of depolymerization is obtained at higher levels of the hydrated filler, possibly due to the lack of filler-polymer interactions tethering silicone rubber chains. Internal oxidation promoted with lower sizes of alumina tri-hydrate could promote a radical-based crosslinking, leaving a stronger shield of residue against dry-band arcing. However, hydrolysis may take place and insignificant improvement is shown for the erosion performance with internal oxidation.

The Effect of the type, size and level of organoclay nanoparticles on the dielectric properties of polypropylene nanocomposites is investigated at different temperatures. Two types of nanoclay, synthetic and natural, are added to polypropylene at different levels. The incorporation of nanoclay into polypropylene is shown to increase the dielectric losses. Unlike the unfilled polypropylene, both real and imaginary part of the permittivity increases at low frequencies with the increase in the clay level. Such a finding can be related to the effect of the interface between the nanoclays and the host PP matrix. The effect of compatibilizer added, i.e maleic anhydride, on the losses at very low frequencies is more recognizable at 80 °C. This could be due the conductive nature of the maleic anhydride at higher temperatures. Lower losses were measured for the polypropylene filled with 2 wt% synthetic nanoclay as compared to polypropylene filled with 2 wt% of natural nano clay. This finding can be attributed to the effect of the size (aspect ratio) of the platelets., IEEE Conference on Electrical Insulation and Dielectric Phenomena, October 22-25, 2017, Worth, TX, USA

The following topics are dealt with: electric breakdown; permittivity; filled polymers; partial discharges; space charge; transformer oil; ageing; power cable insulation; nanocomposites; power transformer insulation., 2018 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), October 21-24, 2018, Cancun, Mexico

This paper investigates the erosion of silicone rubber composites filled with various fillers. The fillers under study are alumina tri-hydrate, magnesium hydroxide and silica in a liquid silicone ru bber. The inclined plane tracking and erosion test was used to compare the erosion of the composite materials at 50 wt% filler level and at 4.5 kV. Simultaneous thermogravimetric and differential thermal analyses are reported which shows various mechanisms by which the fillers can su ppress the dry­ band arcing erosion. The effect of water of hydration in the alumina tri-hyd rate and magnesium hydroxide is investigated and its effect on the suppression of the dry-band arcing erosion is reported for the composites filled with alumina tri-hydrate and magnesiu m hydroxide., 2017 IEEE Conference on Electrical Insulation and Dielectric Phenomenon (CEIDP), 22-25 October 2017, Fort Worth, TX, USA

International audience; A power transformer outage has a dramatic financial consequence not only for electric power systems utilities but also for interconnected customers. The service reliability of this important asset largely depends upon the condition of the oil-paper insulation. Therefore, by keeping the qualities of oil-paper insulation system in pristine condition, the maintenance planners can reduce the decline rate of internal faults. Accurate diagnostic methods for analyzing the condition of transformers are therefore essential. Currently, there are various electrical and physicochemical diagnostic techniques available for insulation condition monitoring of power transformers. This paper is aimed at the description, analysis and interpretation of modern physicochemical diagnostics techniques for assessing insulation condition in aged transformers. Since fields and laboratory experiences have shown that transformer oil contains about 70% of diagnostic information, the physicochemical analyses of oil samples can therefore be extremely useful in monitoring the condition of power transformers.

Frequency Domain Spectroscopy (FDS) is an effective tool allowing assessing the condition of oil-paper insulation system in power equipment. However, results from these measurements are known to be greatly influenced by various parameters, including insulation aging, moisture content, and insulation geometry/volume, together with environmental condition such as temperature. In this contribution, a series of experiments have been performed under controlled laboratory conditions. The dielectric response of the oil impregnated paper, along with the degree of polymerization and moisture content, were monitored. Since dielectric parameters are geometry dependent, poles (independent of the geometry) which depends on resistivity and permittivity, were considered to assess the condition of the insulation. From the investigations performed on new and aged samples, it is shown that poles (P) can be regarded as insulation aging indicator. It is also shown that a per unit value based on the Dielectric Dissipation Factor (DDF), measured in the frequency range from 1 to 1000 Hz can be correlated to moisture content in the insulation paper.