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Thermal conductivity enhanced by the addition of inorganic fillers such as, natural silica has been shown as critical factor improving the erosion performance of silicone rubber filled with micro-sized silica in the inclined plane tracking and erosion test (IPT). In this research, different thermal characteristics of SiR composites filled at 50 w% with natural silica of different median particle sizes (2, 5 and 10 μm) are investigated in both the condensed and gas phases. The thermal conductivity was shown to decrease from 0.5905 W/m.K with 10 μm silica to 0.5230 W/m.K with 2 μm silica, despite the interaction promoted between the 2 μm silica and the polymer. Accordingly, the improvement in the thermal conductivity of SiR by the addition of micro-sized natural silica was elucidated from different perspective than the filler-SiR interaction. The suppression of depolymerization was more evident with 2 μm silica due to the enhanced interaction between the filler and the polymer as indicated by the thermogravimetric and differential thermal analyses., 2020 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), Oct. 18-30, 2020, East Rutherford, New Jersey (Held Virtually)

This paper investigates the influence of nano sized alumina trihydrate and fumed silica fillers on suppressing the DC erosion of hybrid silicone rubber composites containing micron-sized alumina trihydrate filler. Fumed silica was found to be more influential on enhancing the thermal conductivity of the composites compared to nano alumina trihydrate, which is possibly a result of the better filler dispersion of the former. Thermogravimetric analysis suggests the effectiveness of fumed silica in suppressing depolymerization of silicone rubber as a result of silica's favourable interaction with the silicone polymer. Furthermore, the thermal analyses outcomes indicate a significant absorbed moisture content in nano alumina trihydrate which could have adversely impacting the residue characteristics and poorly suppressed silicone rubber depolymerization. In addition, a high temperature endotherm for micro sized alumina trihydrate filler was found indicating the possible decomposition of boehmite to release water molecules promoting the internal oxidation of silicone rubber at high temperature. Outcomes of the +DC inclined plane tracking erosion test correlate with those of the thermal analyses indicating a more influential role for fumed silica's interface in enhancing the DC erosion performance of silicone rubber despite the silica hybrid composite having a lower thermal conductivity than micro alumina trihydrate filled silicone rubber., 2021 IEEE Electrical Insulation Conference (EIC), June 7-28, 2021, Denver, Colorado [Virtual Event]

In this letter a deep learning-based model is proposed for online inspection of silicone rubber outdoor insulators. The inclined plane tracking and erosion test is used as per ASTM D2303 in order to simulate standard erosion on silicone rubber insulation composites. Photos taken for the tested composites are used as training and testing inputs for a convolutional neural network topology in the proposed deep learning model, thereby classifying the degree of erosion damage into light, moderate and severe. The remarkable classification accuracy obtained shows the potential of utilizing the proposed framework for online monitoring of outdoor silicone rubber insulators in the transmission and distribution grid.

This paper investigates the effect of ground and fumed silica fillers on suppressing DC erosion in silicone rubber. Fumed silica and ground silica fillers are incorporated in silicone rubber at different loading levels and comparatively analyzed in this study. Outcomes of the +DC inclined plane tracking erosion test indicate a better erosion performance for the fumed silica filled composite despite having a lower thermal conductivity compared to the ground silica composite. Results of the simultaneous thermogravimetric and thermal differential analyses are correlated with inclined plane tracking erosion test outcomes suggesting that fumed silica suppresses depolymerization and promotes radical based crosslinking in silicone rubber. This finding is evident as higher residue is obtained with the fumed silica filler despite being filled at a significantly lower loading level compared to ground silica. The surface residue morphology obtained, and the roughness determined for the tested samples of the composites in the dry-arc resistance test indicate the formation of a coherent residue with the fumed silica filled composite. Such coherent residue could act as a barrier to shield the unaffected material underneath the damaged surface during dry-band arcing, thereby preventing progressive erosion. The outcomes of this study suggest a significant role for fumed silica promoting more interactions with silicone rubber to suppress DC erosion compared to ground silica fillers.

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.

Outdoor insulators have been widely recognized as backbone components installed in the power system in order to maintain a reliable power supply. The ability of outdoor insulating materials to withstand different weathering conditions in different outdoor environment high voltages has been an important task defined for both suppliers and users of outdoor insulators in the power industry. The use of standard material screening methods is an essential step conducted in order to qualify outdoor insulating materials for their targeted high voltage applications. Various standard guides have been developed, but the need remains to update or create new guides addressing new challenges in the power system. The main aim of this technical committee is to develop IEEE guides on evaluation methods of high voltage insulation materials in the outdoors. The following objectives can be highlighted in achieving this aim: • Providing a scheduled forum such as workshops, special sessions and meetings, addressing new challenges in the industry. • Conducting technical activities such as round robin testing and state-of-the-art literature surveys on recent advances. • Publishing review articles, position papers and special issues in the journals of DEIS.

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

This paper analyzes silicone rubber housing materials that have been aged in service in 200 kV and 400 kV transmission line systems in the Gulf region. Non-uniform discoloration with traces of white residue are more evident across the upper and lower sides of the 400 kV as compared to the 200 kV sheds located near both the energized and the ground ends of the insulators. Scanning electron microscopy (SEM) showed an increase in the roughness for all the surfaces of the materials analyzed as compared to the bulk. Surface oxidation was indicated by the increase in the Oxygen/Carbon (O/C) ratio determined using energy dispersive X-ray (EDX) and the existence of the silanol groups (Si-OH) as detected in the Raman spectroscopy. The effect of electric field causing surface discharges oxidizing the surface was more evident on the 400 kV as compared to the 200 kV materials, particularly on the lower side of the sheds located near the energized end of the insulators. The effect of photo-oxidation due to ultra violet radiation appears to be increasing as compared to the electric field enhancement on the upper side of the sheds, particularly for those located near the ground end of the insulators. Thermogravimetry analysis is found useful in indicating the relative amount of alumina tri-hydrate filler and the polymer in the silicone rubber housing composition. Both O/C ratio determined using EDX and the silanol groups detected using Raman spectroscopy are proposed as reliable aging indicators to assess the condition of the silicone rubber surfaces that have been aged in service under relatively light polluted conditions. Raman spectrometry has the additional advantage as portable Raman spectrometers can be used to conduct field measurements on site.

Evaluating the electrical tracking and erosion resistance of polymeric housing materials is an essential task performed in the development of outdoor insulators. “Tracking” means the formation of a surface carbonaceous path, and “erosion” means weight loss of the housing material. An absolute measurement of the tracking and erosion resistance is not possible; only relative ranking of composites can be achieved using the standard tracking and erosion tests. During the early use of organic insulating materials, failure due to tracking was a major concern, and therefore standard screening methods were proposed to evaluate the tracking rather than the erosion resistance. Erosion has become more important following the development of tracking resistant composites containing high levels of inorganic fillers.

Ghunem, Refat/0000-0002-0951-4775 WOS: 000337137900017 In this paper, a novel selection algorithm of wavelet-based transformer differential current features is proposed. The minimum description length with entropy criteria are employed for an initial selection of the mother wavelet and the resolution level, respectively; whereas stepwise regression is applied for obtaining the most statistically significant features. Dimensionality reduction is accordingly achieved, with an acceptable accuracy maintained for classification. The validity of the proposed algorithm is tested through a neuro-wavelet-based classifier of transformer inrush and internal fault differential currents. The proposed algorithm highlights the potential of utilizing synergism of integrating multiple feature selection techniques as opposed to an individual technique, which ensures optimal selection of the features.

The paper describes a study into understanding the mechanism by which alumina tri-hydrate suppresses dry-band arcing erosion of silicone rubber under DC. Commercial silicone elastomers filled with alumina tri-hydrate to 25 and 58 wt% are exposed to the inclined plane tracking/erosion tests while simultaneously monitoring surface temperature. During the early stages of testing, a surface residue is formed, which promotes stable dry-band arcing. An earlier inception of the stable discharge, thus initiation of deep erosion at a temperature approaching 400 °C, is obtained with 25 wt% alumina tri-hydrate. A lower temperature rise is obtained for the 58 wt% filled specimens as compared to the 25 wt% filled specimens. Differential scanning calorimetry shows a larger enthalpy of dehydration for 58 wt% alumina tri-hydrate filled samples. To verify the role of dehydration on reducing the surface temperature and erosion, the erosion of liquid silicone rubber specimens is compared for samples filled with alumina tri-hydrate and silica, both at 30 wt%. As a measurement parameter, the time-to-erosion is compared between the specimens showing a reduced time for the silica filled specimens as compared to the alumina tri-hydrate filled specimens, thereby verifying the influence of the water of hydration to suppress surface temperature and erosion. The paper provides an experimental approach by which the suppression of erosion by alumina tri-hydrate can be investigated, employing simultaneous leakage current and temperature measurements., 2013 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP 2013), October 20-23, 2013-10-23, Chenzhen, China