Search

This article investigates the filler barrier effect on suppressing the erosion of silicone rubber composites during the dc dry-band arcing, by supplementing main microfillers in silicon rubber, i.e., ground silica and micro-sized alumina trihydrate, with fumed silica and nano-sized alumina trihydrate fillers. A study framework employing simultaneous thermogravimetric-differential thermal analyses (TGA-DTAs), the inclined plane tracking and erosion test, and the dry-arc test is employed. Fumed silica in silicone rubber increases the amount of the crosslinked residue and suppresses silicone rubber depolymerization, whereas nano-sized alumina trihydrate releasing water of hydration may adversely impact the residue coherence and promote combustion. The viability of the filler barrier effect is synergistically achieved by adding fumed silica to the main ground silica filler, thereby maintaining the residue integrity. The inclined plane-tracking erosion test confirms the importance of the filler barrier effect of fumed silica in supplementing the volume effect of ground silica in the suppression of the dc dry-band arcing. These filler effects appear to mainly govern the erosion resistance, with insignificant effect shown for thermal conductivity under dc. The dry-arc resistance test is shown as a useful method to simulate a stable dry-band arcing and obtain reproducible surface erosion patterns that correlate with the outcomes of the dc inclined plane tracking and erosion test.

The aim of this paper is to present a review of the development and application of superhydrophobic insulation for outdoor high voltage applications. The methods of preparing insulation exhibiting superhydrophobic properties in order to mitigate the pollution problem under high voltages in the outdoors are explored. In addition, existing evaluation techniques at the material development stage are reviewed and potential new modifications are discussed. The self-cleaning and anti-icing properties, the electrical performance and prospects of superhydrophobic insulators are also addressed. Although superhydrophobic insulators may show promising behavior in small-scale laboratory conditions that do not employ electrical stress, the effect of surface micro-nano structure responsible for the superhydrophobicity on performance under the actual outdoor and weathering conditions under voltage remains to be fully understood and verified. Therefore, there is a need to verify the feasibility of superhydrophobic insulators for outdoor high voltage applications with a solid evaluation protocol, while employing material screening methods in the laboratory, and with reference to field experience.

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 study investigates the role of filler interface on suppressing the erosion of room temperature vulcanized silicone rubber composites filled with fumed silica, nano alumina trihydrate and sub-micron hexagonal boron nitride fillers during DC dry-band arcing. Simultaneous thermogravimetric-differential thermal analyses indicate a superior effect for fumed silica in suppressing the depolymerization of silicone rubber and promoting radical based crosslinking. This can be attributed to favorable interactions at the fumed silica-silicone interface tethering the siloxane chains. At low filler loading of alumina trlhydrate, water of hydration has insignificant effects on suppressing depolymerization compared to that influenced by fumed silica's interface at equal filler loading. Similarly, incorporating thermally conductive boron nitride filler in silicone rubber does not show improvement in the depolymerization rate compared to that influenced by fumed silica. These findings correlate with the +DC inclined plane tracking and erosion test outcomes indicating superior erosion performance for the fumed silica filled composite. This accordingly supports the influential role of the filler interface over the water of hydration and thermal conductivity enhancement in suppressing the DC erosion of silicone rubber composites under the test conditions of this study. A statistical boxplot analysis technique is introduced to elucidate the inception of the stable dry-band arc in terms of the change in leakage current randomness during the +DC inclined plane tracking and erosion test. The boxplots reveal a slow inception of the stable dry-band arc with the fumed silica filled composite delaying the erosion of silicone rubber during the test. This finding confirms the influence of the filler interface over composite thermal conductivity in suppressing erosion of silicone rubber under DC dry-band arcing.

In this paper, a stochastic framework is proposed for optimizing replacement strategies of aged XLPE cables in the electric power distribution network. The proposed framework facilitates realizing an economic value for the risk of unplanned outages, thereby shifting the paradigm of replacing aged XLPE cable from a technical decision that is solely based on diagnostic measurements to a techno-economic strategy. The proposed framework constitutes of three main phases: (1) obtaining a distribution for the aging process of XLPE cable due to water-trees, (2) modeling the replacement of the aged XLPE cable as a Markov decision process, and (3) applying a linear programming algorithm in order to solve for the optimal replacement policy. Based on the proposed framework, a critical health index is defined for optimum replacement, depending on the installation costs of a new cable and the unplanned outage cost.

With growing environmental concerns, biodegradable insulating fluids are being investigated as alternatives to petroleum-based mineral insulating oil in power transformers. In order to optimize their use, decomposition studies of these alternative fluids are therefore of ultimate importance. This paper investigates the thermal decomposition kinetics of mineral oil and two vegetable-based ester fluids, using the thermogravimetric analyses. The initial and maximal decomposition temperatures are determined using thermal analyses. In addition, the Arrhenius activation energy is calculated for the fluids under study using the Ozawa-Flynn-Wall iso-conversional method. In addition, TGA studies are extended to mineral and natural ester impregnated paper, with the aim of assessing their impact on the thermal decomposition of insulation paper. It is found that the level of mono-unsaturated acids in esters is important for enhancing the thermal stability. The enhanced thermal stability of the esters has advantageously contributed to the improvement of the thermal performance of the insulation paper., IEEE Conference on Electrical Insulation and Dielectric Phenomena (IEEE CEIDP 2021), December 12-15, 2021, Vancouver, Canada

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 residue formed on silicone rubber filled with natural silica in the inclined plane tracking and erosion test under AC and DC voltages. Simultaneous thermogravimetric and differential thermal analyses reveal residue formation dependent on volatilization and crosslinking in silicone rubber. Thermo-oxidation of volatiles yields silica-based residue protecting the surface during dry-band arcing; whereas, crosslinking leaves carbonaceous residue leading to more severe dry-band arcing. Volume fraction of natural silica replacing silicone rubber is shown to be a main source of silica residue suppressing carbonaceous residue, thus preventing failure in the inclined plane test. More severe erosion under the equivalent +DC voltages as compared to standard AC and equivalent - DC voltages of the inclined plane test is attributed to more severe dry-band arcing heat promoted by carbonaceous residue. Silicone rubber filled with lower particle sizes of natural silica is demonstrated to deteriorate erosion performance, possibly as result of filler-polymer interactions or lower particle size reducing the integrity of the protective silica residue. The following paper highlights the importance of using critical AC and DC voltages during the inclined plane tracking and erosion tests.

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.

This paper aims to investigate the effect of nano-sized alumina tri-hydrate on the DC erosion resistance of silicone rubber, using the inclined plane tracking and erosion test. Silicone rubber composite containing nano-sized alumina tri-hydrate is comparatively analyzed with reference to silicone rubber filled with fumed silica at loading level of 5 wt%. Moreover, commercial silicone rubber composites that contain micro-sized alumina tri-hydrate at high loading levels are used for reference. Thermal characterization of silicone rubber composites is presented using simultaneous thermogravimetric and differential thermal analyses. The results obtained indicate a correlation between the erosion resistance determined using the inclined plane tracking and erosion test under DC voltages and the level of interaction between the filler and the silicone rubber tethering the siloxane chains, thereby suppressing the depolymerization and promoting crosslinking of silicone rubber. It also appears that the loading level of nano-sized alumina tri-hydrate is an essential factor that needs to be considered in order to obtain an evident erosion suppression effect for the water of hydration., 2019 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), Oct. 20-23, 2019, Richland, Washington, USA

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.

Moisture in transformer paper insulation is one of the most important parameters to be monitored in order to assess the useful life of the transformer. Time domain spectroscopy based on polarization and depolarization current measurements is one of the methods that can be used for detection of moisture content in the transformer paper insulation. However, these measurements could be influenced by thermal transient during the application of voltage, which may lead to an inaccurate interpretation of the insulation condition. In this paper, a novel method is proposed in order to avoid this thermal transient effect by using the high frequency component of the of depolarization current acquired during the measurement. Preliminary results show a correlation between the high frequency component of the depolarization current waveform and the moisture content in the paper insulation within a moisture content range of about 3 %. At higher moisture content, a resistive leakage current seems to have a negative effect on the measured depolarization current., 2019 IEEE 20th International Conference on Dielectric Liquids (ICDL), June 23-27, 2019, Roma, Italy

This paper discusses the lessons learned about fillers that are added to silicone rubber insulation housing composites, in order to improve the erosion resistance against the dry-band arcing are presented and common perceptions. Common practices that employ alumina tri-hydrate are reviewed, including the additional influential effect of the water of hydration in the suppression of the dry-band arcing. The effect of the water of hydration is shown to be dependent on various factors, such as the hydrated filler level and the type of the hydrated filler. More recent paradigms in which hydrated fillers have not been employed are also reviewed. Volume and shield actions of fillers are essential aspects that need to be understood in the design of silicone rubber insulation housing composites for new applications such as HVDC. In addition, the thermal degradation mechanisms of silicone rubber and the corresponding suppression effects of the added fillers are summarized.

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

The paper reviews previous work on the DC inclined plane test and suggests equivalent DC voltage levels in parallel to AC voltage in the ASTM inclined plane tracking and erosion test. The aim of this work is to provide a basis for standardizing the inclined plane test for DC voltage. Round robin tests done in five laboratories on five specimens of a silicone rubber material were done with the purpose of establishing appropriate ratios by which the equivalent DC voltages can be determined with respect to the corresponding AC voltages. These levels were determined as 67% and 87%, for +DC and –DC respectively, of the AC initial tracking voltage, and for practical purposes, these levels are rounded to 70 and 90%.

This paper describes the suppression of dry-band arcing erosion of silicone rubber by alumina tri-hydrate and silica fillers in the DC inclined plane test, employing the wavelet based multiresolution analysis of leakage current. The third detail component of the leakage current as decomposed by the wavelet-based multiresolution analysis is shown to be an indicator of the effectiveness of the filler type in suppressing erosion by dry-band arcing. The addition of alumina tri-hydrate or silica filler to silicone rubber increases the thermal conductivity of the composites, retarding the development of the eroding temperature, and thus the evolution of the third detail. Additional effect is also obtained for the dehydration enthalpy, of alumina tri-hydrate in silicone rubber at a filler level of 30 wt%, in impeding the development of hot spots on the tested surface. A reduction in the magnitude of the third detail is evident with filler level, indicating that the increasing volume of silica or alumina tri-hydrate reduces the temperature of the dry-band arcing plasma. Comparable levels of the leakage current third detail is found between 30 wt% alumina tri-hydrate and silica filled composites which suggests the water of hydration plays a minor role in diluting the SiR but at 58 wt% an internal oxidation mechanism that produces gases diluting the arcing phase appears to suppress erosion.

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

The first polymer insulator for AC transmission lines was developed in the late 1950s. This insulator consisted of a flexibilized epoxy resin weathershed cast onto a fiberglass rod, and field trials on a 138-kV line took place in 1959. Insulators failed almost immediately on energization due to severe tracking and erosion of the bisphenol-A epoxy material, which was later, through inclined-plane tests, shown to be inherently unsuitable for use in outdoor insulation [1].

This paper describes an investigation into the dry-band arcing mechanism leading to erosion of filled silicone rubber in the DC inclined plane test. Good correlation is obtained between the formation of surface residue, hotspots and the eroding dry-band arcing. The hotspots detected by infrared camera correlates well with the temperature of degradation determined by thermogravimetric analysis and differential scanning calorimetry. To characterize the physical mechanism of dry-band arcing, wavelet-based multiresolution analysis up to seven levels of resolution is applied to the leakage current waveforms. The analysis shows that both stable and intense discharges characterize the eroding dry-band arcing. A time-to-eroding parameter is proposed to determine the relative resistance to the formation of residue. Faster accumulation of residue is evident under -DC than +DC. Earlier inception of erosion is obtained for the silica filled- as compared to the alumina tri-hydrate filled- silicone, in which the release of the water of hydration is postulated to suppress the residue formation.

The main objective of this study is to investigate the feasibility of using an RF antenna to detect and classify partial discharges on polymer insulation surfaces. The detected discharges are identified based on their originating sources, employing a cascade of feature extraction, feature selection and the standard artificial neural network classifier. Both statistical and spectral analyses have been used for feature extraction. Feature extraction is followed by a feature selection stage with a novel implementation of stepwise regression method in order to derive representative feature vectors, yet with minimum dimensionality. Suppression of redundant features is therefore achieved, thereby enhancing the classification reliability. Finally, classification is performed using a standard feed forward neural network with back propagation training algorithm. The proposed method is found to be successful in classifying different types of partial discharge with recognition accuracy exceeding 96%. The proposed method can be an essential stage towards overhead line inspection to assess the status of outdoor polymer insulators, where partial discharges could be initiated from surface discharges due to pollution and/or from corona discharges from energized ends.

In this paper, the performance of silicone rubber composites containing 0, 10 and 30 wt % loading of silica filler is investigated in the initial-tracking voltage test method of the inclined plane test under AC and DC showing the most inferior erosion class under +DC followed by -DC and then AC. DC as compared to AC dry-band arcing characteristics are analyzed by conducting leakage current measurements prior to and after the inception of dry-band arcing. At high test voltages, instability of the contaminant rivulet is found to be an important factor in the development of dry band arcing and, consequently, biasing the test outcomes when equal voltages of rms AC and DC are selected. The initial tracking voltage in ASTM D2303 is, therefore, proposed as a reliable approach by which +DC and -DC test voltages can be reliably selected. A coefficient of variation parameter is also proposed as a useful mean of selecting the equivalent DC voltages, and the validity of the parameter is verified experimentally using the initialtracking voltage test method. Erosion in the constant voltage method is investigated under DC by applying the equivalent voltages and compared to AC. Based on this methodology, it is suggested that an improvement in silicone rubber compositions is needed for DC. Moreover, the need to select the creepage distance of polymer insulators designed for AC, yet to be used under DC, with reference to tracking/erosion performance is highlighted.

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.

In this paper Raman spectroscopy is performed on silicone rubber housing materials that have been taken from 200 kV and 400 kV transmission line insulators, located in the Gulf region. The service areas of these insulators feature heavy depositions of sands and dusts yet with intermittent durations of fog and wetting on the surface. In addition, the creepage distances have been selected for heavily polluted conditions as per IEC 60815, thereby expecting light aging conditions for the analyzed housing materials. The increase in the Raman band intensity of Si-OH rationed to the Raman band intensity of Si-O-Si is found as a useful aging indicator for the analyzed surfaces. On the other hand, a careful analysis is required when using the Raman band intensity of alumina tri-hydrate rationed to the Raman band intensity of Si-O-Si in order to indicate the reduction in the polymer content due to aging. Ultra-violet radiation oxidizing the surface is the main factor reported to deteriorate the analyzed materials. An increased influential effect is also speculated for both the aging time in service for the 200 kV insulators and for electric field enhancement inducing surface discharges as approaching the energized side of the 400 kV insulators. Using Raman spectroscopy to assess the condition of service-aged silicone rubber insulators can be advantageous as, with a special apparatus, this method can be implemented on site., 2016 IEEE Conference on Electrical Insulation and Dielectric Phenomena (CEIDP), October 16-19, 2016, Toronto, ON, Canada

With the deregulation of the power system network, prioritizing capital investments and reducing operational costs while maintaining a reliable supply has become a priority for asset managers in utilities. A shift from a corrective-or time-based to a condition-based maintenance strategy for the utility infrastructure has therefore become an essential task. For example, a significant portion of the underground medium voltage XLPE cables in the electricity grid has been in service for periods longer than their nominal designed life, and therefore an asset management decision has to be taken to replace, refurbish or maintain these cables in service. Such a decision requires a reliable condition assessment method based on accurate diagnostic measurements that can determine the health index of the cable-under-test (CUT)., 2016 Conference on Precision Electromagnetic Measurements (CPEM 2016), July 10-15, 2016, Ottawa, ON, Canada

In this paper a prediction model is proposed for estimation of furan content in transformer oil using oil quality parameters and dissolved gases as inputs. Multi-layer perceptron feed forward neural networks were used to model the relationships between various transformer oil parameters and furan content. Seven transformer oil parameters, which are breakdown voltage, water content, acidity, total combustible hydrocarbon gases and hydrogen, total combustible gases, carbon monoxide and carbon dioxide concentrations, are proposed to be predictors of furan content in transformer oil. The predictors were chosen based on the physical nature of oil/paper insulation degradation under transformer operating conditions. Moreover, stepwise regression was used to further tune the prediction model by selecting the most significant predictors. The proposed model has been tested on in-service power transformers and prediction accuracy of 90% for furan content in transformer oil has been achieved.

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.

In this paper condition assessment of silicone rubber coating applied to high voltage insulators is proposed. Electrical, thermal and chemical measurement methods are used to evaluate the condition of silicone rubber coating. From an asset management perspective, hydrophobicity is shown to be the key indicator of aging, and thus the remnant life, of the coating material. The increase in the content of surface oxygen is an indicator of hydrophobicity deterioration under the power system stresses. In addition, detecting the diffusion of the low-molecular-weight siloxane from the bulk to the surface can be utilized to indicate the relative ability to recover hydrophobicity after aging.

In this paper a parametric study of the dry-band arcing characteristics in the inclined plane tracking and erosion test is conducted under AC and DC voltages. The standard inclined plane testing apparatus is modified to promote stable and intense dry-band arcing, thereby analyzing the characteristics of the eroding dry-band arcing. The behavior of the liquid contaminant, which may bias the dry-band arcing current under equal AC and DC voltages, is investigated for different flow rates to determine suitable testing conditions. The highest leakage current magnitude is obtained under +DC followed by AC and -DC voltages, and reduced resistivity for the dry-band arcing column is shown under the +DC and AC as compared to the -DC voltages. The reduction in resistivity is speculated to be the result of metallic ions from electrode corrosion under +DC as compared to -DC, with less significant difference between +DC and AC. In addition, the inception behavior of the discharge influencing the length of the dry-band arc is found to be dependent on the voltage type. Reduced dry- band arcing length is measured for DC as compared to AC, with further reduction shown under +DC as compared to -DC. Thermal analysis is accordingly conducted, showing higher hot spot temperatures with dry-band arcing of a shorter length.

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

The paper presents comparative inclined plane test results of high temperature vulcanized silicone rubber and EPDM elastomers filled with alumina trihydrate to 25 wt% under DC. Both the initial tracking voltage and the constant voltage test methods are employed to evaluate the relative tracking/erosion resistance of both elastomers. While insignificant differences between the tracking/erosion resistance of the two elastomers is observed, earlier failure occurs under -DC. A recognizable distinction is also found between the failure pattern and the corresponding dry-band arcing current. Shorter non-conduction periods in the leakage current are observed on the silicone rubber elastomer prior to failure, a result that indicates stable discharge activity, which is more evident under +DC than under -DC. Imbedded in the stable dry band arcing current are transient leakage current pulses due to probable ionization activity, which can be seen to enhance the intensity of the discharge. In contrast, intermittent dry band arcing current is found to be dominant for the EPDM elastomer.

In this paper the leakage current signature in the DC inclined plane test is examined for statistical indicators of the incipient erosion of silicone rubber. The mean, skewness and kurtosis are examined as useful indicators of the dry-band arcing current causing erosion. The moving window method is employed during the test to obtain an enhanced resolution in time. Simultaneous thermogravimetric-differential scanning calorimetry analysis is used to predetermine the temperature at which erosion begins, and temperature measurements taken during the inclined plane test are correlated to the leakage current leading to erosion. During erosion, more stable discharges as well as a recognizable change in the statistical distribution of the dry-band arcing current is recognizable through the analysis employed.

Insulation resistance (IR) or Megger test has been commonly performed in both preventive and corrective maintenance activities to verify power transformers' insulation condition. Other insulation diagnosis tests such as oil breakdown voltage (BDV), water content and dissolved-gas-in-oil analysis have been conducted along with the IR test. In this paper, a prediction model is developed to correlate IR measurements of the power transformer with its oil quality parameters, the concentration of its total dissolved combustible gases (TDCG), and its carbon dioxide to carbon monoxide concentration (CO 2/CO) ratio. Four models, based on feed-forward artificial neural networks with back-propagation, are trained on collected data of real measurements. Accuracy levels of 96%, 84%, 88%, and 91% are obtained for BDV, water content, TDCG, and CO2/CO ratio respectively. Utilizing the proposed model can reduce maintenance costs by preventing and shortening transformers' outage times using inexpensive test, i.e. using IR test only. 2012 IEEE. Scopus

In this paper erosion of silicone rubber loaded with 30 wt% ATH and silica is investigated in the DC inclined plane tracking/erosion test as per ASTM D 2303. Reduced equivalent DC voltages have been applied in order to compare with the erosion under AC. Hot spot temperatures are used for comparative analysis of dry-band arcing severity on the tested materials. Also, depending on the type of filler, initiation of stable and intense dry-band arcing is discussed. Based on the results it is proposed that the existing material formulation used for AC insulators are not suitable for DC insulators as the erosion is more severe and different.

The tracking voltage in the inclined plane test with AC is compared to the tracking voltage with DC, using the initial-tracking-voltage test method as per ASTM D2303 and a proposed coefficient of variation parameter. The severity of DC, as opposed to AC voltage, on RTV silicone rubber materials is confirmed using both strategies, where +DC is found to be the most severe voltage. The leakage current waveforms are found to consist of two components corresponding to wetting of the surface and to dry-band arcing. The mean value of the leakage current is a reflection of the wetting of the surface; whereas, the leakage current variation is a reflection of the dry-band arcing. Accordingly, a coefficient of variation parameter is proposed as an indicator of the relative severity of the dry band-arcing. Employing this coefficient of variation parameter, the ratios of the equivalent +DC and -DC to AC initial-tracking voltage are attained for 30 wt% silica filled two-part RTV silicone rubber. The results obtained using the coefficient of variation parameter have been verified experimentally using the initial-tracking-voltage in ASTM D2303.

The main objective of this study is to investigate the feasibility of using an RF antenna to detect partial discharges in outdoor insulators. Moreover, the study focuses on identifying the sources of partial discharge using artificial neural networks. In outdoor insulators, partial discharges could be initiated either from surface discharge due to pollution and/or from corona discharges from energized ends. Both statistical and spectral features have been used as an input vector to a feed forward neural network with back propagation training algorithm. The proposed method is found to be successful in classifying different types of partial discharge with a recognition accuracy of 93%. The proposed method can be used during overhead line inspection to assess the status of outdoor non-ceramic insulators.

The potential of having a more efficient and cost-effective source of power in the market has driven the incentive to inject distributed generation through smart grids. Distributed generation has been proposed to be a source of sustainable energy. However, the increased use of power electronic devices linking the distributed generation to the existing grid can produce a considerable amount of harmonics. Moreover, the use of power factor correction capacitors at the distributed generation interfacing the grid can amplify the harmonic distortion level due to system resonance. Thus, the injected frequency components to the grid can play a significant role in introducing enhanced stresses on the electrical insulation system on vital power system components; like transformers. In this paper, the effect of the harmonics' injection, as a consequence of the distributed generation interface to the grid, on the degradation of the transformer insulation system is studied. Experiments on degrading transformer paper insulation samples with harmonic-polluted voltages are performed. Dissipation factor increment ratio is used as a measure of the aging effect on insulation. It has been found that the dissipation factor increment ratio of the transformer paper insulation is significantly higher, when stressed with distorted voltage waveforms compared to the power frequency voltage stresses.

The concentration of furanic compounds in transformer's oil can be an effective measurement towards assessing the aging state of oil impregnated paper in the transformer. The rate of change of the concentration of furan content is vital for assessing the rate of deterioration of cellulose insulation and its severity. This promotes furan content as effective parameter in transformer oil for transformer condition assessment and accordingly asset management. In this paper the correlation between oil parameters and furan content is studied using artificial neural networks (ANN). A neural network is used for predicting the furan content based on different combinations of input parameters that are known to be correlated to cellulose paper degradation of the transformer. These input parameters are carbon monoxide (CO), carbon dioxide (CO2), water content, acidity, and break down voltage (BDV). Results on real data of forty transformers show that the proposed model is capable of predicting the furan content with an average accuracy of 90%. Consequently, this proposed model improves the efficiency of oil chemical tests and dissolved gas analysis (DGA) and their abilities to assess the condition of transformer solid insulation.