Partial Discharge Resistance Research Articles

Electrical Characterization of Boron Nitride-Filled Insulation for Aerospace and Avionics Applications

The environmental challenges associated with high-power, high-voltage electrified aircraft require a targeted approach with regard to the development of next-generation aerospace electrical insulation. This study reports findings on polyphenylsulfone (PPSU) as a matrix material based on its unique thermal, mechanical, and dielectric properties, filled with hexagonal boron nitride (h-BN) with micron- and nanoscale particulates. The inorganic ceramic filler was selected for its thermally conductive and electrically insulating performance in extreme environments. The main goal was to investigate the dielectric strength and electrical resistance (endurance) to partial discharges (PDs). Since PDs are a leading accelerated degradation phenomenon causing premature failure in organic electrical insulation, the capability of an insulating material to endure PD-induced degradation for the whole (or part of) its design life is of paramount importance. It was observed that incorporation of h-BN micro fillers can significantly improve the PD resistance, even in comparison with insulating materials typically used for electrified transportation, such as corona-resistant Kapton. It was also observed that a suitable combination of micro and nano fillers can also be used as a viable solution to increase the electrical performance and reliability of the avionics insulation components.

Shielding Strategies for Electric Field Minimization in Current Transformers: A Finite Element Combined Design of Experiment Approach

The internal electric field distribution is a key factor to characterize the partial discharge and voltage resistance of current transformers (CTs), and the conical current transformer has a special structure with complex electric field distribution. Therefore, it is more necessary to study, analyze and optimize the electric field distribution of CTs in the design process. In this paper, a new type of current transformer is taken as the research object. A simulation model is established by using finite element software, and the electric field distribution under the test of power-frequency withstand voltage is investigated. Then, a scheme is proposed, and the response surface is used to optimize the scheme. Experimental verification is conducted to validate the results. In this study, the finite element combined design of experiment approach can serve as a rapid and efficient approach for identifying an optimal solution to minimize the electric field strength within a current transformer.

Dielectric, Mechanical, and Thermal Properties of Crosslinked Polyethylene Nanocomposite with Hybrid Nanofillers

Crosslinked polyethylene (XLPE) nanocomposite has superior insulation performance due to its excellent dielectric, mechanical, and thermal properties. The incorporation of nano-sized fillers drastically improved these properties in XLPE matrix due to the reinforcing effect of interfacial region between the XLPE-nanofillers. Good interfacial strength can be further improved by introducing a hybrid system nanofiller as a result of synergistic interaction between the nanofiller relative to a single filler system. Another factor affecting interfacial strength is the amount of hybrid nanofiller. Therefore, the incorporation amount of hybridising layered double hydroxide (LDH) with aluminium oxide (Al2O3) nanofiller into the XLPE matrix was investigated. Herein, the influence of hybrid nanofiller content and the 1:1 ratio of LDH to Al2O3 on the dielectric, mechanical, and thermal properties of the nanocomposite was studied. The structure and morphology of the XLPE/LDH-Al2O3 nanocomposites revealed that the hybridisation of nanofiller improved the dispersion state. The dielectric, mechanical, and thermal properties, including partial discharge resistance, AC breakdown strength, and tensile properties (tensile strength, Young's modulus, and elongation at break) were enhanced since it was influenced by the synergetic effect of the LDH-Al2O3 nanofiller. These properties were increased at optimal value of 0.8 wt.% before decreasing with increasing hybrid nanofiller. It was found that the value of PD magnitude improvement went down to 47.8% and AC breakdown strength increased by 15.6% as compared to pure XLPE. The mechanical properties were enhanced by 14.4%, 31.7%, and 23% for tensile strength, Young's modulus, and elongation at break, respectively. Of note, the hybridisation of nanofillers opens a new perspective in developing insulating material based on XLPE nanocomposite.

Partial Discharge Current Measurements With Small Discharge Gaps Over Polyimide Film

Partial discharge (PD) characteristics obtained with small gaps are very important to determine the PD resistance of polymers in power equipment. Particularly, PD characteristics of polymers used in small-sized power equipment, such as the power module of an electric vehicle instead of a gasoline engine, have become very important. Among polymer insulating materials, polyimide (PI), which is widely used for circuit mounting, is selected as our target insulating film sample. To understand PD mechanisms in depth, we measure nanosecond PD pulse current waveforms instead of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\varphi $ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${q}$ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${n}$ </tex-math></inline-formula> characteristics, which have been the mainstream of PD studies. Although numerous studies have used the amount of PD charge integrated from the PD pulse current, few studies have measured the high-speed nanosecond PD pulse current itself, which is easily buried in noise. In this study, we measure PD waveforms under an ac peak voltage of 2000 V and more at 50–1000 Hz to clarify the waveforms to understand low-voltage PD characteristics. The electrode system is a simple needle-plane electrode with small discharge gaps of 0, 75, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$150 ~\mu \text{m}$ </tex-math></inline-formula> . The current direction from the high-voltage electrode to the PI film is determined as a “positive current.” We found that the positive current magnitude is almost twice the negative one, whereas the negative current forms have almost half the duration time of that of the positive ones at almost all applied voltage frequencies. The waveform difference between positive and negative pulse indicates charge origin difference as electrons and ions. This study contributes to the understanding of PD mechanisms.

Enhancement of Partial Discharge Resistant Characteristics of XLPE Nanocomposites Using Plasma Treatment Technique

Polymer nanocomposites are well-known for their superior insulation properties over the existing polymer insulating material due to the existence of nanoparticles. However, the agglomeration of the nanoparticles within the polymer matrix is the main factor that restricts the enhancement of insulation characteristics because the nonuniform dispersion of nanoparticles reduces the interfacial area and creates weak polymer-nanofiller interfacial bonds. Thus, the main contribution of this work is conducting a comprehensive technique of nanoparticle surface modification using atmospheric pressure plasma (APP) to improve the surface compatibility between nanoparticles and polymer matrix, consequently enhancing insulation properties. In this study, the APP with the homogeneous and stable discharge was used in treating the surface of silicon dioxide (SiO2) nanoparticles to enhance its compatibility with cross-linked polyethylene (XLPE) matrices. In comparison with unfilled XLPE, the most effective formulation of XLPE nanocomposites was shown by the sample with 3 wt% of plasma-treated SiO2 nanoparticles with a reduction of partial discharge (PD) magnitude up to 62.85% and the reduction of PD numbers up to 26.70%. Plasma has proven to be a comprehensive technique to improve the PD resistance of XLPE nanocomposites by exciting the formation of more substantial interfacial regions through forming interfacial bonds and reducing the size and number of agglomerated clusters.

Investigation of partial discharges in non-woody kenaf based pressboard under influence of moisture

The most crucial parts that decide the transformer’s lifetime are the solid insulation of the power transformer, especially the pressboard and kraft paper. The life of the insulation is significantly influenced by the presence of water in the insulation. This paper presents a study on partial discharge (PD) on the existing normal pressboard (NP) and the newly developed Kenaf-polypropylene pressboard (KPP). Also, the moisture content of the pressboard varied between 0%, 1%, and 3% by the percentage weight of different methods. After the initiation of PD, the surface deterioration analysis was performed by using scanning electron microscopy (SEM). The results from the study revealed that KPP shows superior performance in mitigating PD. At 0%, 1% and 3% moisture contents, KPP showed 89%, 83% and 25% reductions in average PD magnitude, respectively. Overall, the kenaf composite pressboard has better PD resistance, which is one of the things to think about when insulating a transformer.

Improvement of partial discharge resistance of polypropylene under AC voltage by blending elastomer

This paper reports on the partial discharge (PD) erosion characteristics of polypropylene (PP)/elastomer blends where ethylene-octene copolymer elastomer (EOC) and propylene-based elastomer are involved. The PD erosion is performed through a pair of needle-to-plane electrodes by applying 5 kV AC voltage for 2 h. A high-frequency current transformer, optical recorder, and ozone sensor are used to capture the information released during the PD erosion process. In addition, a 3D optical profilometer is employed to record the erosion profile, from which the erosion depth and the surface roughness can be extracted. Carrier trap distribution is derived from the isothermal surface potential decay measurement. The influences of elastomer type and content on the PD resistance are analyzed. The results show that the resistance is improved with the addition of elastomer, and the blend containing EOC of 20 wt% has the best PD resistance among all samples, which is 61.9% higher than that of the pure PP. It is proposed that the carrier trap characteristics, the property of elastomer, and the free volume in the material play important roles in the improvement of the PD resistance. This work provides a potential method to enhance the PD resistance of PP by blending elastomer with proper type and content.

Effects of nanofiller and voltage stabilizer on partial discharge resistance of polypropylene/elastomer blends: A comparison study

AbstractThis paper reports on the individual and synergistic influence mechanisms of nano‐silica (SiO2) and voltage stabilizers on partial discharge (PD) resistance of polypropylene blended with ethylene‐octene copolymer elastomer. The SiO2 nanoparticles and three types of voltage stabilizers, that is, benzoin, 4,4′‐dimethoxybenzil, and 3‐aminobenzoic acid are selected as fillers to prepare samples. PD is initiated in a rod‐to‐plane electrode system with an alternating current voltage of 5 kVrms. PD characteristics are captured with multi‐sensors, and the erosion profile of the test sample is measured using a three‐dimensional (3D) optical profilometer. Carrier trap distribution is extracted with isothermal surface potential decay measurement to assist the analysis of PD eroding material. Fourier transform infrared spectrum, scanning electron microscopy, X‐ray diffraction spectrum, and differential scanning calorimetry analysis are performed to reveal the change in material structures caused by the fillers. Test results indicate that the PD resistance of the blend can be improved by the addition of nano‐SiO2 and voltage stabilizers individually and synergistically. The PD resistance of PO is increased by 71.2% at most in the sample with 3 wt% nano‐SiO2 addition. The sample filled with SiO2 exhibits better PD resistance than that with the voltage stabilizer or co‐added, which should be ascribed to the introduction of deep traps, the formation of the packaged layer, the suppression of oxygen diffusion of the nanofillers, and the good compatibility between additives and the polymer matrix.

Research on Improving the Partial Discharge Initial Voltage of SiC/EP Composites by Utilizing Filler Surface Modification and Nanointerface Interaction.

SiC/EP composites are promising insulating materials due to their high thermal conductivity, stable chemical properties, and nonlinear electrical conductivity. However, the compatibility of micron-sized SiC particles with the organic polymer matrix is poor, and defects such as air gaps may be introduced at the interface, which reduces the partial discharge resistance of the composite materials. In order to improve the partial discharge initial voltage (PDIV) of SiC/EP composites, in this paper, SiC/EP composites with different proportions were prepared by surface modification of filler and compound of micro/nano particles. Firstly, a method of secondary modification of SiC particles was proposed, which was first modified by alkali washing and then silane coupling agent KH560, and the effectiveness of the modification was verified. Therefore, the interface bonding ability between the filler and the matrix was improved, the air gap defects at the interface were reduced, and the PDIV of the composite material was improved. When the filling ratio is 10 wt%, the PDIV was enhanced by 13.75%, and when the filling ratio was further increased, the improvement was reduced. In contrast, the introduction of nanoparticles into the composites can effectively improve the PDIV of composite materials. In this study, nanoparticles were used to form a shell-core structure in epoxy resins to exert their huge specific surface area and active surface properties, thereby changing the overall crosslinking properties of the composites. Through experimental research, the optimal micro-nano particle compounding ratio was explored. Under the optimal mixing ratio, the PDIV of the composite material can be increased by more than 90%.

Plasma Treated Low-Density Polyethylene Nanocomposites: Investigation of Partial Discharge and Breakdown Strength

Polymeric insulating materials have been widely used in high voltage equipment, particularly in power cables, as insulating material, due to their excellent performances. This study investigates the significance of atmospheric pressure plasma (APP) treatment on silicon dioxide (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) nanoparticles in enhancing the partial discharge (PD) resistance and breakdown strength of low-density polyethylene (LDPE) nanocomposites. The duration of plasma treatment was manipulated for 15 and 30 minutes to identify the effects of treatment duration on their dielectric properties. The loading of fillers was varied into 1, 3, and 5 wt% to identify the promising formulations. The results exhibited that the dielectric properties of LDPE nanocomposites have improved as the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles were treated, anticipated due to the surface activation via functionalizing hydroxyl group on the fillers as ultimate oxidation agent, resulting in reduced size of agglomerated clusters. The PD resistance and breakdown strength have increased up to 47% and 70% of the unfilled samples, respectively, as the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanoparticles were treated using plasma. Plasma treatment was found to be an alternative technique for improving the filler-polymer surface interaction, at once promising the better dielectric properties of LDPE nanocomposites, potentially prolonging the lifetime of the insulating materials.

AC Breakdown Voltage and Partial Discharge Activity in Synthetic Ester-Based Fullerene and Graphene Nanofluids

This paper deals with the study of the AC breakdown voltage (BDV) and partial discharges (PDs) activity of synthetic ester-based nanofluids (NF) with two kinds of carbonic nanoparticles (NPs), namely graphene (Gr) and fullerene (C₆₀); the synthetic ester (SE) being Midel 7131. The BDV measurement was achieved at various concentrations of NPs and different electrodes gap distances, while the partial discharges activity was studied only at the optimal concentration that gave the best improvements of BDV. First, a detailed improved procedure for preparing our NFs is presented. Then, the zeta potential measurements are performed on these NFs, and their stability is checked. After the preparation and characterization of samples, the BDVs and PDs parameters are measured according to IEC 60156 (modified gap distance) and IEC 60270 standards, respectively. Finally, conformity of the experimental data with Normal and Weibull distributions is examined, and the BDV at cumulative probabilities of 1&#x0025; and 50&#x0025; are then deduced. It is shown that BDV outcomes for all studied liquids obey both Normal and Weibull distributions, and the BDVs at cumulative probabilities of 1&#x0025; and 50&#x0025; are improved. Moreover, adding Gr and C₆₀ nanoparticles at different concentrations enhances the BDV values for investigated electrode gaps (0.1 to 2.0mm). The best improvement is obtained with a concentration of 0.4 g/L for 0.5mm and 0.7mm electrode gap with fullerene and Graphene nanoparticles, respectively. For a 2mm gap distance, the best improvements are of about 12.67&#x0025; and 16.64&#x0025; with 0.4g/L of C₆₀ and 0.3 g/L of Gr, respectively. It is also shown that the addition of C₆₀ significantly reduces the activity of partial discharges compared to pure SE, while the addition of Gr destroys the partial discharges resistance of pure SE.

Effects of Plasma Treated Alumina Nanoparticles on Breakdown Strength, Partial Discharge Resistance, and Thermophysical Properties of Mineral Oil-Based Nanofluids.

Mineral oil has been chosen as an insulating liquid in power transformers due to its superior characteristics, such as being an effective insulation medium and a great cooling agent. Meanwhile, the performance of mineral oil as an insulation liquid can be further enhanced by dispersing nanoparticles into the mineral oil, and this composition is called nanofluids. However, the incorporation of nanoparticles into the mineral oil conventionally causes the nanoparticles to agglomerate and settle as sediment in the base fluid, thereby limiting the improvement of the insulation properties. In addition, limited studies have been reported for the transformer oil as a base fluid using Aluminum Oxide (Al2O3) as nanoparticles. Hence, this paper reported an experimental study to investigate the significant role of cold plasma treatment in modifying and treating the surface of nano-alumina to obtain a better interaction between the nano-alumina and the base fluid, consequently improving the insulation characteristics such as breakdown voltage, partial discharge characteristics, thermal conductivity, and viscosity of the nanofluids. The plasma treatment process was conducted on the surface of nano-alumina under atmospheric pressure plasma by using the dielectric barrier discharge concept. The breakdown strength and partial discharge characteristics of the nanofluids were measured according to IEC 60156 and IEC 60270 standards, respectively. In contrast, the viscosity and thermal conductivity of the nanofluids were determined using Brookfield DV-II + Pro Automated viscometer and Decagon KD2-Pro conductivity meter, respectively. The results indicate that the 0.1 wt% of plasma-treated alumina nanofluids has shown the most comprehensive improvements in electrical properties, dispersion stability, and thermal properties. Therefore, the plasma treatment has improved the nanoparticles dispersion and stability in nanofluids by providing stronger interactions between the mineral oil and the nanoparticles.

Application and Suitability of Polymeric Materials as Insulators in Electrical Equipment

In this paper, the applications of thermoplastic, thermoset polymers, and a brief description of the functions of each subsystem are reviewed. The synthetic route and characteristics of polymeric materials are presented. The mechanical properties of polymers such as impact behavior, tensile test, bending test, and thermal properties like mold stress-relief distortion, generic thermal indices, relative thermal capability, and relative thermal index are mentioned. Furthermore, this paper covers the electrical behavior of polymers, mainly their dielectric strength. Different techniques for evaluating polymers’ suitability applied for electrical insulation are covered, such as partial discharge and high current arc resistance to ignition. The polymeric materials and processes used for manufacturing cables at different voltage ranges are described, and their applications to high voltage DC systems (HVDC) are discussed. The evolution and limitations of polymeric materials for electrical application and their advantages and future trends are mentioned. However, to reduce the high cost of filler networks and improve their technical properties, new techniques need to be developed. To overcome limitations associated with the accuracy of the techniques used for quantifying residual stresses in polymers, new techniques such as indentation are used with higher force at the stressed location.

액상실리콘고무/나노 실리콘카바이드 복합체의 부분방전 저항성 특성

For the development of HVDC cable connector, Nano SiC was corroded in H₂O₂ to form Si-OH . On the basis of SiR, Nano SiC was chemically treated with vinylsilazane. Samples were prepared by homogeneously dispersing the modified Nano SiC in silicon according to the doping level content (0, 1, 3, 5, 7, 9 wt%). It is to develop a controllable material with nonlinear conductivity that can homogenize electrical stress in HVDC cable connectors. In addition, in order to develop a material with strong partial discharge resistance and thermal conductivity, high voltage stress was applied for 500 hours in a 5kV/720Hz environment. As a result, the erosion depth of the surface was measured. Heat conduction was measured and evaluated to investigate the effect of high voltage stress on heat conduction.

The effect of silica content to partial discharge characteristic of low-density polyethene and natural rubber blend as the electrical insulator

The dielectric properties of low-density polyethylene natural rubber (LDPE-NR) biopolymeric insulating materials can be improved by adding the silica nanoparticles in a certain percentage of weight (w%). In the present study, four types of bio-nano polymeric samples were prepared. To each sample, the nanosilica particles with wt% 1.5%, 3%, 4.5% and 6%. As one characteristic of dielectric, the partial discharge (PD) characteristics, each sample has been tested for 1 hour under AC high voltage field, and the pulses were counted for each sample and grouped into positive and negative pulses. The PD pattern was also plotted based on X-Y axes, namely Φ-q-n pattern. It was found that the number of positive and negative partial discharge (PD) pulses for each silica sample after 60 minutes of testing varied for all samples. It is also found that samples with a higher percentage of nanosilica had fewer PD pulses. The PD pattern in lower w% of silica was identified in the 90 degrees mostly in containing This indicates that w% of nanosilica particles can improve the PD resistance or the insulation quality of LDPE-NR insulation materials.

Electrical Treeing and Partial Discharge Characteristics of Epoxy/Silica Nanocomposite under Alternating Current

The hydrophilic surface of fumed nanosilica was modified to a hydrophobic surface by treating it with a trimethyl silane coupling agent, and epoxy nanocomposites were prepared by mixing the modified nanosilica (0 phr, 1 phr, 3 phr, 5 phr, and 7 phr) in an epoxy matrix, where the unit phr means the parts per one hundred grams of epoxy base resin. To apply the nanocomposites to heavy electrical equipment, the effects of the modified nanosilica on the long-term treeing phenomena and the partial discharge (PD) resistance were studied under high voltage alternating current (HVAC) conditions. The bonding of trimethyl silane on the nanosilica surface was confirmed by the appearance of new peaks for the CH2 and CH3 groups in Fourier-transform infrared spectroscopy analysis. To observe the even dispersion of the modified nanosilica particles in the epoxy matrix, a transmission electron microscope was employed, and it was found that 1 phr of the modified nanosilica was uniformly dispersed; however, as the nanosilica content was increased, its aggregation became somewhat severe. The longest HVAC treeing breakdown time was found in an epoxy nanocomposite with 1 phr of alkyl-modified nanosilica, and the time was 17,412 min, which was 143.9 times longer than the 121 min required for a neat epoxy system. In a nanocomposite with 5 phr of modified nanosilica, PD resistance was found to be 12.5 times higher than that of the neat epoxy system.

Effect of AC stressed aging on partial discharge, thermal and tensile performance of silicone rubber-based composites

In this paper, partial discharge characteristics of the multi-stressed aged and un-aged high temperature vulcanized silicone rubber (HTV-SR) samples with several concentrations of alumina trihydrate (ATH) and silica are studied. This is to elucidate whether the addition of nano/micro fillers of silica and ATH in silicone rubber enhances the resistance against partial discharges and aging behavior under different weathering conditions. Further, performance assessment is made by thermogravimetric analysis, differential scanning calorimetry and through measurement of tensile strength. Using IEC (b) electrode system, partial discharge measurements are performed according to IEC 60270. From these experimental measurements, it has been observed that by adding filler contents, the multi-stress aging performance improved and partial discharge resistance is enhanced up to 40% as compared to the HTV-SR without any filler. Moreover, through analysis of data obtained by thermogravimetric, indicate that nano doping increases the physical and chemical cross-linking points which confine the motion at the particle-matrix interface. As a result, the enhanced thermal stability of the composites. Considerable improvement in the stress-strain behavior of test samples is also observed with the addition of silica and ATH.

Investigation of Electrical Tree Growth of XLPE Nano Composites using Time–Frequency Map and Clustering Analysis of PD Signals

Failure of underground cables due to electrical treeing phenomena, i.e. formation of electrical discharges in the imperfections of cable insulation, is a major problem faced by electrical utilities. Many research works on nanocomposites are being carried out to improve the electrical treeing resistance of the XLPE cable insulation material. Technological advancements in communication and data analytic systems have shown the way for implementing online continuous partial discharge (PD) monitoring systems for high voltage apparatus. Hence collection of PD database of XLPE nanocomposites in the laboratory during entire electrical tree growth process is important for implementing efficient condition monitoring systems and relatively little work has been published in this area. In this work, PD characteristics of XLPE nanocomposites with 1, 3, 5 and 10 wt% silica were investigated. Electrical tree growth and corresponding phase resolved PD (PRPD) pattern were analysed with respect to time. Cluster analysis of equivalent time–frequency mapping of PD signals was carried out with respect to tree growth time period. Statistical analysis was performed for the entire set of PD data. Results show that cluster analysis of T–F map of PD data is useful in estimating early failure of insulating material due to treeing. Addition of silica nano fillers in the range of 3–5 wt% concentration significantly improves the PD resistance and breakdown time of XLPE material.

PVC nanocomposites for cable insulation with enhanced dielectric properties, partial discharge resistance and mechanical performance

The current study aims to develop polyvinyl chloride (PVC) nanocomposites with enhanced electrical and mechanical properties by incorporating titanium oxide (TiO2) nanoparticles within PVC chains. Different loading of nanoparticles and different nanoparticle surface states were considered. The surface states are unfunctionalised, functionalised using vinyl silane and functionalised using amino silane. The choice of a most suitable surface state was a critical factor that guarantees a good dispersion of nanoparticles and consequently enhances the compatibility between TiO2 and PVC matrix. The process followed in the PVC/TiO2 nanocomposites preparation, loaded with different wt.% of TiO2 nanoparticles, was the solvent method. The dielectric properties measured here were the relative permittivity (ɛr), dielectric loss (tanδ), breakdown strength (AC and DC under uniform field) and the internal partial discharges (PDs) within insulation cavity. All measurements have been performed under room temperature and at frequency ranged from 20 to 1.0 MHz. Furthermore, the mechanical properties of the samples like elongation, elasticity modulus and tensile strength were also studied. Vinyl silane showed better improvements in both electrical and mechanical performances compared to the amino silane, especially in cases of high weight fractions of TiO2. This is because of the improvement in the PVC-TiO2 interfacial region arise from the similarity of polarity and surface tension values of vinyl silane with that of PVC matrix and TiO2 nanoparticles.

Effect of micro and nano-size boron nitride and silicon carbide on thermal properties and partial discharge resistance of silicone elastomer composite

This study introduces silicone elastomers with micro and nano-sized boron nitride (BN) and silicon carbide (SiC) particles with various doping levels to improve thermal properties and partial discharge resistance. The effect of micro and nano-fillers on thermal conductivity, coefficient of thermal expansion (CTE), and thermal stability are investigated. Polarization and depolarization current and partial discharge are measured to investigate the non-linear conductivity, trap energy density distribution, and partial discharge resistance. Experimental results show higher thermal conductivity, lower CTE, and better thermal stability than the original silicone elastomer. Large size fillers dominate the thermal conductivity when the doping level is low, whereas the composite microstructure plays a significant role in the thermal conductivity when the doping level is high. The combination of different filler type and size has less effect on thermal stability and CTE compared to the effect of the doping level. According to the depolarization current, the composite's trap depth is generally shallower than that of the original silicone elastomer. With increased doping level, the shallow trap density increases, providing hopping sites for carriers, whereas the deep trap density decreases, reducing the number of trapped charges. The partial discharge inception voltage is higher than that of the original silicone elastomer, and it increases with the doping level, which may be because the electrostatic field generated by diffused charges reduces the local electric field near the high voltage electrode.