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Graphene has attracted much attention due to its advanced properties. In previous work, the relationship between temperature and the conductivity of epoxy-based nanocomposite filled with graphene oxide has been experimentally studied. To understand the charge transport behaviour, the space charge characteristics at different temperatures and field...
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Space charge measurement accuracy is crucial when assessing the suitability of cables for high-voltage direct current (DC) systems. This study assembled state-of-the-art analysis technologies, including time-domain deconvolution, to mark electric field estimation accuracy, which the present techniques achieve. The pulse electroacoustic method was a...
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... The electric field-driven de-trapping and transport processes allowed certain amounts of space charge to reach gas-solid interfaces, forming surface charge accumulation. To explore the effect of space charge behaviors on surface charge distribution with regularity, ergodic simulation settings based on previous literature results [45][46][47][48][49][50] were considered, with trap density varying from 50 to 650 C m À3 and trap level changing from 1.00 to 1.15 eV, under an applied voltage of 10 kV at 40 C. As shown in Fig. 3(a), three homopolar potential peaks exist on the surface of the post insulator: negative potential peak I located near the ground electrode, positive potential peaks II and III near the high-voltage electrode. ...
Long-term operation of high voltage direct current at elevated temperatures can result in the accumulation of surface charges in DC gas-insulated transmission line (GIL) insulators. Such a phenomenon leads to localized electric field distortion, increasing the risk of surface discharge. The analysis of interaction behaviors between surface charge and space charge at interfacial domains of GIL insulators is a complex task, which requires a comprehensive understanding of physical mechanisms of the gas–solid interface charging. In this work, a two-dimensional bipolar charge transport and interaction (2D BCTI) model is established, with the consideration of both surface and space charge dynamics. Pulsed electroacoustic tests and surface potential measurements are conducted on DC GIL insulator materials under different electrical-thermal coupling conditions. Experimental results exhibit great consistency with the predictions from the 2D BCTI model. The local accumulation of space charge near interfaces has certain effects on surface potential distribution, which in turn influences charge injection behavior from electrodes. In comparison to traditional surface charge simulation models, the consideration of space charge–surface charge interaction behaviors proves to be essential for estimating the polarity and amplitude of surface potential distribution. This model holds promise for assessing charge characteristics in electrical equipment where direct measurement is challenging.
... When the filler content was 0.5 wt%, the breakdown strength increased by 32.1%. In addition to insulating fillers, semiconductive fillers (such as SiC) 14 and conductive fillers (graphene) 15 have also shown promising performance in reducing space charge accumulation and improving the breakdown strength. Besides, Zhao 16 studied the effect of SiO 2 particle size on charge transport and the breakdown strength of SiO 2 /EP epoxy nano-composite, and the results revealed that the amount of charge accumulated was positively correlated with the size of SiO 2 particles. ...
Thermal and mechanical properties of Al2O3/epoxy nano-composite, composed of bisphenol A diglygde ether (DGEBA) as matrix and 3,3-diaminodiphenyl sulfone (DDS) as curing agent filled with Al2O3 nanoparticles in spherical, cubic, or tetrahedron shapes, are investigated through molecular dynamics simulations. Constant temperature constant pressure ensembles and annealing cycles are utilized for modeling thermodynamic equilibrium systems in a wide temperature range. It is verified that all the three shaped Al2O3 nano-fillers can effectively improve heat-resistant and mechanical performances of epoxy polymer, in which sphere Al2O3 nano-fillers are the most significant in promoting mechanical stiffness and render an elevated glass transition temperature by 13.5 K. All three different shaped Al2O3 nano-fillers are capable of efficiently reducing thermal expansion coefficient and fractional free volume, accounting for the evident improvement in heat resistance, in which sphere and cubic Al2O3 nano-fillers are more preferential for decreasing thermal expansion coefficient by 13.92% and 12.66% respectively. Al2O3/epoxy nano-composite represents a substantial amelioration in elastic modulus, which is especially significant in the temperature range around glass transition temperature.
... Du et al. found that when there is the introduction of an appropriate amount of nano graphene oxide into low-density polyethylene materials, it will have more deep traps, thereby inhibiting the accumulation of space charge and the distortion of the electric field, but when the doping nanofiller content is high, the trap level becomes shallow [15,17]. Liu et al. studied the characteristics of single-layer and multi-layer graphene oxide doped epoxy composites and found that EP/GO composites not only inhibit charge transfer but also introduce deep traps [18]. It can be found that studies have shown EP/GO as the insulator material in gas insulation equipment has a good prospect. ...
Trapped space charges in epoxy composite distort the electric field, which will induce the failure of the insulation system, and nano graphene oxide may inhibit the curing behavior of epoxy resin matrix. This paper analyzes how the two interfaces affect the electron traps of epoxy resin/graphene oxide systems with different nanofiller contents. The electron affinity energy of epoxy resin matrix and nano filler molecules in the epoxy resin/graphene oxide system is calculated based on quantum chemistry. It is found that nano graphene oxide has a strong electron affinity energy and is easier to capture electrons. Then the influence of the interface formed by the epoxy resin matrix and the nano graphene oxide on the electron transfer ability is calculated. The epoxy resin matrix contains the electron transfer ability of interfaces formed by nano graphene oxide and the molecular chain is different from that of unreacted molecules. The results can provide a reference for the modification of epoxy resin/graphene oxide nanocomposites.
... 10 Gallot-Lavallée et al. 11 found that, at higher temperatures, hetero charges replace the homo charges. The space charge performances of the epoxy with multilayer graphene oxide (MGO) at different temperatures is investigated in 12 and showed that the space charge accumulation could be suppressed with the introduction of the MgO particles supported by the simulation results. For the epoxy composites filled with MgO, the homo charges are mainly found at low temperatures, whereas the hetero charges are observed at 120 C. 13 The least space charge accumulation was achieved from 0.5 wt% epoxy/SiO 2 nanocomposites due to the lowest imaginary part of the dielectric constant at high temperature. ...
This article investigates the high‐temperature space charge dynamics of epoxy composites consisting of micro and nano‐AlN fillers under a high electric field. The test temperatures are selected for the space charge measurement based on the glass transition temperature. An indigenously designed pulse electro‐acoustic system measures the space charge distribution up to 150°C. The stepwise‐increasing field is applied to the test samples from 20 to 100 kV/mm at the rate of 20 kV/mm. The epoxy hybrid composites show negligible space charge accumulation at room temperature and low electric fields, which increases at high temperatures and high electric fields. The hybrid composite with 1 wt% nanoparticle has a dielectric breakdown at 100 and 150°C under 100 kV/mm with an evident amount of accumulated charges. In the hybrid composites with 3 and 5 wt% nanofillers, the breakdown is observed under 80 and 100 kV/mm, respectively, at 150°C. Notably, the micro‐nano filler addition significantly improves the thermal conductivity of the epoxy resin. The uniform dispersion of the fillers affects the electrical and thermal properties of the epoxy. The charge dynamics‐related mechanism is proposed on the basis of morphological characterization and thermal properties of epoxy and its composites.
... Various studies have reported that nanofiller addition significantly enhances the electrical and thermal properties of EP, apart from thermal conductivity [6][7][8][9][10][11][12][13][14]. This issue was formulated by combining microfillers with nanofillers in the base material, referred as hybrid composites. ...
This paper investigates the electrical and thermal properties of the pure epoxy resin (EP) and its micro-nano hybrid composites (20 wt% micro-AlN fillers with 1 wt% and 3wt% nano-Al2O3 fillers; 50% micro-AlN with 3% nano-Al2O3 fillers) for the power electronic packaging application. The electrical properties such as space charge distribution, electrical conductivity and surface potential decay are measured. The thermal performance of the fabricated samples is estimated using the thermal analyzing devices. The hybrid composite consisting of 20 wt% micro-AlN and 1 wt% nano-Al2O3 fillers exhibit the least space charge accumulation, higher thermal conductivity and better thermal stability. However, the excessive addition adversely affects space charge and electrical conductivity properties. The micro-nano hybrid composites significantly exhibit higher electrical conductivity than pure EP. The microfiller addition from 20 wt% to 50 wt% significantly improves the thermal conductivity of the EP. The reduced space charge injection and accumulation in the hybrid micro-nano composites are attributed to the enhancement of the injection barrier and reduction of the charge carrier traps in these materials. A theoretical mechanism of the charge dynamics inside the samples under different test conditions is proposed to support the experimental results.
... In the existing literature, several investigations have been performed to understand the space charge behaviour in epoxy nanocomposites with different filler materials [15][16][17][18][19][20]. The space charge behaviour of epoxy-MgO nanocomposites were investigated in [15]. ...
... The effect of gamma radiation on space charge accumulation in epoxy-micro and nanocomposites were studied in [19]. Similarly, space characteristics of epoxy-graphene oxide nanocomposite were discussed in [20]. However, very few have investigated the charge trapping characteristics of the epoxyalumina nanocomposites. ...
In this study, the relationship between thermal ageing and charge trapping properties of epoxy-based nanocomposites has been investigated. With ageing, any dielectric material undergoes thorough degradation. This degradation significantly affects the space charge accumulation and charge trapping behaviour of the dielectric, which are very important parameters for insulation health under high-voltage direct current (HVDC) environment. In this work, an improved model based on the isothermal relaxation current (IRC) has been developed to study the charge trapping behaviour of pure epoxy and epoxy alumina (Al(2)O(3)) nano-composites at different ageing conditions. A methodology based on polarisation–depolarisation current (PDC) measurements has been proposed to identify the current component due to a dipolar relaxation in measured total IRC. This will help to identify the trap distribution characteristics more accurately compared to conventional IRC measurements. It was experimentally observed that the addition of nanoparticles significantly reduces trapped charge formation and reduces thermal degradation. It is observed that aging leads to the generation of deeper traps, while the addition of Al(2)O(3) nanoparticles mainly enhances the density of shallow traps. Results presented in this work indicate that epoxy–alumina nanocomposites are very much suitable in HVDC applications from the perspective of trapped charge accumulation.
... It is pointed out in [25], that the GO filler has the large number of functional groups on the GO surface. These groups will become unstable and be dissociated into ions under high electric field, which may result in more heterocharges accumulation leading to the enhancement of local electric filed strength [26]. On the other hand, the higher DC conductivity as shown in Figure. ...
Field grading within the dry-type bushing insulation presents a major challenge for DC applications due to the highly temperature-dependent conductivity of the epoxy resin insulation. An electric field regulation method based on the epoxy/graphene oxide (EP/GO) nanocomposites with the reduced temperature coefficient of conductivity is proposed and investigated in this paper. DC conductivity of EP/GO nanocomposites with different loadings of 0, 0.05, 0.1 and 0.5 wt% at various temperature are investigated. Trap level distributions are characterized by the isothermal discharge current (IDC) method to clarify the conduction mechanism. Obtained results show that more shallower traps are introduced and the thermal activation energies of the nanocomposites are reduced by the GO nanoparticles, indicating that the temperature coefficient of conductivity of the nanocomposites is reduced. The improvement of electric field distribution within the bushing insulation under operating voltage is verified when the EP/GO nanocomposite with an appropriate content is employed, based on an established 1800 kV valve-side bushing for a converter transformer. However, more defects will be introduced by the GO fillers with excessive content (0.5 wt%), resulting in an obvious reduction of the DC breakdown strength.
... Previous studies have shown that space charge has a great influence on the breakdown characteristics of nanocomposite dielectrics [16,17] . However, it seems not much research has been conducted with respect to the influence of nano fillers on the molecular structure of the matrix in the process of breakdown. ...
The wide application of nanocomposites in the insulation system has greatly contributed to the performance improvement of power equipment. However, nano fillers are not omnipotent for improving the properties of composite dielectrics. In some situations, nano-modified materials are in fact a compromise of improving some performance features while sacrificing others. In this work, the breakdown characteristics and time-to-failure of polypropylene film with nano-clay fillers have been evaluated under combined thermal stress and AC electric fields. Experiments on plain polypropylene (PP) samples have also been carried out under the same test conditions as control. Test results indicated that the time-to-failure of the samples with nano-clay filler was shorter than those without nano filler, which is different from the previous experience. SEM and EDS analyses were conducted to study how the failure mechanism had taken place in both plain polypropylene and the nano-clay filled polypropylene. The failure phenomenon in these materials can be explained by molecular thermodynamics. The main reason for the premature thermal breakdown of PP nanocomposite is essentially due to the weak coupling between nano-clay filler and polymer matrix. Finally, suggestions are proposed for nano modification methods and lifespan prediction models of composite dielectrics.
... Du et al have found that certain content of GO nanoparticles could introduce large quantities of deep carrier traps in LDPE/GO [19]. S. Zhang et al have found that epoxy resin filled with GO has lower apparent mobility, deeper trap depth and larger number of trapped charges compared to pure EP [20]. GO is an oxide of graphene, while graphene has an enormous specific surface area of 2630 m 2 •g -1 , thereby GO retains the advantages of large specific surface area of graphene [21]. ...
Surface charge accumulation under DC stress is a critical factor in reducing the insulation performance of epoxy-based nanocomposite. Surface coating has been used to inhibit the charge accumulation, but the inhibition mechanism of the coating material is still unclear. In this paper, graphene oxide (GO) and silicon carbide (SiC) have been selected as fillers to prepare the coating material with epoxy as the base material. The role of GO on surface charge inhibition performance of epoxy/SiC coating has been estimated. The test results showed that the charge inhibition performance increased with the growth of nano-SiC content from 1 wt% to 5 wt% in the epoxy/SiC coating. As regards the epoxy/(SiC+GO) coating, the charge inhibition performance reduced as the SiC content increased. It is suggested that the charge inhibition performance of epoxy/SiC coating can be improved with a low content addition of GO. The variation of trap distribution in the coating material caused by the GO should be responsible for the enhanced charge inhibition behavior.
