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Space charge accumulation in the cable insulation will cause local electric field distortion, and accelerate the aging of the material. The inner semi‐conductive layer as an important structure of cable will affect the charge injection characteristics in the insulation layer. This work intended to explore the method of modifying the semi‐conductive layer with the Nitrogen‐doped graphene (NG) to suppress the charge accumulation utilizing the super‐smoothness of graphene and electron adsorption of N element. First, the NG is prepared using N‐modified graphene, and the semi‐conductive layer with different NG content is fabricated. Second, the physical and chemical properties of the semi‐conductive composite are carried out, then the charge accumulation characteristics in the insulation layer under the effect of the semi‐conductive layer are characterized. The results showed that an appropriate amount of NG doping can significantly inhibit the charge accumulation in the insulation layer. The surface roughness decreased by about 32.13% when the doped NG content is 0.5 phr. With the increase of NG content from 0 to 1 phr, the accumulation charges inside the insulation layer decreased by about 36.84%. This research provided a new approach for suppressing space charge accumulation in the insulation material of high voltage cable. [ABSTRACT FROM AUTHOR]

The great potential of K 1/2 Bi 1/2 TiO 3 (KBT) for dielectric energy storage ceramics is impeded by its low dielectric breakdown strength, thereby limiting its utilization of high polarization. This study develops a novel composition, 0.83KBT-0.095Na 1/2 Bi 1/2 ZrO 3 -0.075 Bi 0.85 Nd 0.15 FeO 3 (KNBNTF) ceramics, demonstrating outstanding energy storage performance under high electric fields up to 425 kV cm -1 : a remarkable recoverable energy density of 7.03 J cm -3 , and a high efficiency of 86.0%. The analysis reveals that the superior dielectric breakdown resistance arises from effective mitigation of space charge accumulation at the interface, influenced by differential dielectric and conductance behaviors between grains and grain boundaries. Electric impedance spectra confirm the significant suppression of space charge accumulation in KNBNTF, attributable to the co-introduction of Na 1/2 Bi 1/2 ZrO 3 and Bi 0.85 Nd 0.15 FeO 3 . Phase-field simulations reveal the emergence of a trans-granular breakdown mode in KNBNTF resulting from the mitigated interfacial polarization, impeding breakdown propagation and increasing dielectric breakdown resistance. Furthermore, KNBNTF exhibits a complex local polarization and enhances the relaxor features, facilitating high field-induced polarization and establishing favorable conditions for exceptional energy storage performance. Therefore, the proposed strategy is a promising design pathway for tailoring dielectric ceramics in energy storage applications., (© 2024 Wiley‐VCH GmbH.)

In this article, space charge and partial discharge (PD) behavior and the breakdown strength of silicone rubber under ac and dc voltages are tested in high magnetic field. In the case of ac voltage, the effects of high magnetic field on promoting air gap breakdown result in the decrease in PD inception voltage. Polarization of specimens with higher speed and lower air gap breakdown voltage result in the increase in PD frequency and eventually causes the decrease in breakdown strength. In the case of dc voltage, energy level splitting due to Zeeman effects results in lower interface barrier, considering both the increase in electron affinity and the increase in density deference between donor-like and acceptor-like surface traps. The decrease in interface barrier causes more space charge injection. The electric field distortion caused by local space charge accumulation leads to the decrease in breakdown strength in high magnetic field. [ABSTRACT FROM AUTHOR]

This study compares different polymer-nanofiller blends concerning their suitability for application as insulating thermoplastic composites for High Voltage Direct Current (HVDC) cable application. Two polymer blends, PP/EOC (polypropylene/ethylene-octene copolymer) and PP/PP-HI (polypropylene/ propylene - ethylene copolymer) and their nanocomposites filled with 2 wt.% of fumed silica modified with 3-aminopropyltriethoxysilane were studied. Morphology, thermal stability, crystallization behavior dynamic relaxation, conductivity, charge trap distribution and space charge behavior were studied respectively. The results showed that the comprehensive performance of the PP/PP-HI composite is better than the one of the PP/EOC composite due to better polymer miscibility and flexibility, as well as lower charging current density and space charge accumulation. Nanosilica addition improves the thermal stability and dielectric properties of both polymer blends. The filler acts as nucleating agent increasing the crystallization temperature, but decreasing the degree of crystallinity. Dynamic mechanical analysis results revealed three polymer relaxation transitions: PP glass transition (β), weak crystal reorientation (α1) and melting (α2). The nanosilica introduced deep traps in the polymer blends and suppressed space charge accumulation, but slightly increased the conductivity. A hypothesis for the correlation of charge trap distribution and polymer chain transition peaks is developed: In unfilled PP/EOC and PP/PP-HI matrices, charges are mostly located at the crystalline-amorphous interface, whereas in the filled PP/EOC/silica and PP/PP-HI /silica composites, charges are mostly located at the nanosilica-polymer interface. Overall, the PP/PP-HI (55/45) nanocomposite with 2 wt.% modified silica and 0.3 wt.% of antioxidants making it a promising material for PP based HVDC cable insulation application with a reduced space charge accumulation and good mechanical properties.

In high voltage direct current (HVDC) cable systems, study of electric field distortion created by space charge accumulation is very important for examining insulation performance. Therefore, in this paper the influence of space charge on short-time breakdown characteristics of cross-linked polyethylene (XLPE) are studied. Trap energy distribution is an important factor affecting space charge behavior in dielectrics. Dielectrics with various thicknesses exhibit different space charge phenomena due to various trap distribution characteristics, which regulate the injection, migration and accumulation processes of charges. Consequently, trap characteristics can affect many parameters, such as charge accumulation depth and injection barrier. XLPE with thickness less than 100 μm show lower density of deep traps which can accumulate homogeneous bulk charges as compared to thick XLPE with thickness greater than 100 μm. This phenomenon determines the internal field strength distortion rate which is 20% larger for thin XLPE and it is much higher than that for thick XLPE. The external factor which is considered for analysis is applied field strength and it shows a linear proportional affect on the electric field distortion. A quantitative relationship model between applied field strength and distortion field strength of XLPE with different thicknesses was established. Linear extrapolation was used to obtain the trend of applied, distortion, and actual field strengths at different XLPE thicknesses when breakdown occurred. When the thickness of XLPE is less than 100 μm, distortion field strengths is higher than 50kV/mm and increases with decreasing thickness, resulting in a significant effect on the breakdown phenomenon and breakdown strength increases with increasing thickness. And when the thickness of XLPE is greater than 100 μm, the distortion field strengths is less than 50 kV/mm which also confirms the volume effect on breakdown phenomenon and breakdown strength decreases with increasing thickness.

Oil-paper insulation as an irreplaceable insulation system in the electrical power transformer is inevitably suffering the water intrusion on working condition, which will make dielectric performance degraded and insulation aging accelerated. In high interest of explaining the deterioration effect of absorbing moisture on the dielectric properties of oil-paper insulation system and corresponding mechanism, the space charge and trap level characteristics are investigated for the specially prepared oil-impregnated pressboards with different moisture contents. The Pulsed Electro Acoustic and Isothermal Surface Potential Decay experiments are performed to test the space charge distributions and evaluate the trap level depths, respectively. It is indicated that the polarity of injected space charges is alternated with the decaying rate being raised when the absorbing moisture is aggravated in oil-impregnated pressboards. The charge carriers are more prone to be captured by the shallow-level traps that have been introduced by water permeation near pressboard surface than the intrinsic deep-level traps inside pressboard. The captured charge carries accounts for the significantly exacerbated space charge accumulation as manifested by the surface charges of oil-impregnated pressboards.

New potential High Voltage Direct Current (HVDC) cable insulation materials based on nanocomposites are developed in this study. The nanocomposites are produced by blending of polypropylene (PP), propylene-ethylene copolymer (PP–HI) and a modified fumed silica (A-silica) in a concentration of 1 and 2 wt %. The A-silica is successfully modified with (3-aminopropyl)triethoxysilane (APTES) via a solvent-free method, as proven by infrared spectroscopy, thermogravimetry and transmission electron microscope mapping.A-silica in the polymer matrix acts as a nucleating agent resulting in an increase of the crystallization temperature of the polymers and a smaller crystal size. Moreover, the silica addition modified the crystals morphology of the unfilled PP/PP-HI blend. The composite containing A-silica with 2 wt% contains bigger-size silica clusters than the composite filled with 1 wt%. The composite with the higher A-silica concentration shows lower space charge accumulation and a lower charge current value. Besides, much deeper traps and lower trap density are observed in the composite with 2 wt% A-silica addition compared to the one with a lower concentration. Surprisingly, the presence of silica clusters with dimensions of more than 200 nm exhibit a positive effect on reducing the space charge accumulation. However, the real cause of this improvement might be due to change of the electron distribution stemming from the amine-amine hydrogen bond formation, or the change of the chain mobility due to the presence of occluded polymer macromolecules constrained inside the high structure silica clusters. Both phenomena may lead to a higher energetic barrier of charge de-trapping, thus increasing the depth of the charge traps.

In the past few decades, immense contributions have been put in by researchers to measure the accumulation of space charge in dielectric materials. At the same time, the direct measurement of the amount of space charge in materials has been completely neglected, probably due to the difficulties in measuring currents at high-voltage (HV) electrode. Although the amount can be measured indirectly with the available methodologies, the measured results suffer from accuracy issue. Also, indirect measurements involve complex, post measurement mathematical analysis such as deconvolution and filtering to get the amount of accumulated charge. Keeping the lacunas in mind and contrary to the basic approach of the present methodologies, a novel wireless system is developed which separately monitors the ultralow, volumetric, electrode currents flowing into and out of the material at both HV and ground electrodes. The obtained current data are further processed to observe the accurate temporal variation in the accumulated charge using the fundamental concept of charge conservation law. Some more parameters have also been identified which unmistakably determine the presence of the packet-like-charge phenomenon in dielectric materials such as low-density polyethylene. Furthermore, for comparing the results of the proposed electrode system, space charge measurements have been done using pulsed electroacoustic system. Based on the comparison of the results, it is concluded that the newly developed electrode system monitors the charge accumulation closely but with less effort and complexity. [ABSTRACT FROM AUTHOR]

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.

High permittivity materials are currently in use for mitigation of electrical stress in high-voltage apparatus and energy storage systems. In this work, epoxy-based high permittivity nanocomposites with Barium titanate (BaTiO(3)) nanofillers are considered, for the purpose of stress mitigation. Uniform dispersion of the fillers in the polymer up to 10% by volume is achieved. Apart from the use of as-received fillers, the effect of using surface-functionalised nanoparticles (with 3-glycidoxypropyltrimethoxy-silane) before use is also investigated. The nanocomposite is characterised in terms of its complex permittivity, DC conductivity, short-term AC breakdown strength and space charge accumulation, to gauge its suitability for use in high-voltage insulation. Complex permittivity is measured using broadband dielectric spectroscopy over a broad frequency range of 1 mHz to 1 MHz. DC conductivity is studied from polarisation–depolarisation current measurements. Short-term AC breakdown strength tests are performed at power frequency (50 Hz). Space charge density along the sample thickness is obtained using pulsed electro-acoustic technique. A computational case-study is presented to show the feasibility of using the high permittivity nanocomposite for electric stress control in high-voltage equipment (viz., at mounting flanges of 69 kV bushings).

Saturable reactor insulation is currently stressed by an exponential decay pulse voltage under normal operating conditions. The partial discharge (PD) characteristics of epoxy resin under an exponential decay pulse voltage were studied here and were compared at 25 and 110°C. In addition, this study compares these PD characteristics with those under a sinusoidal voltage to better measure the insulation design margin of the saturable reactor under an exponential decay pulse voltage. Finally, this study explains the PD mechanism based on the three-capacitor circuit model and space charge accumulation. Compared with the sinusoidal voltage, a higher amplitude, a higher inception voltage and fewer PDs are obtained under the pulse voltage. The reason may be related to the accumulation of space charge. Due to the duality of the space charge effect, the promotion effect of space charge accumulation on the PD under the pulse voltage is dominant, and an increase in temperature will weaken the promotion effect. In contrast, the inhibitory effect of space charge accumulation on the PD under the sinusoidal voltage is dominant. The experimental results can provide a basis for the optimal design of saturable reactor insulation under an exponential decay pulse voltage.

The Maxwell–Wagner model and bipolar charge transport model both aim at describing the charge transport behaviours in dielectrics. The Maxwell–Wagner model performs well in calculating the polarisation current and electric field distribution, but it is too macroscopic to describe the microscopic behaviours of space charges. The bipolar charge transport model can well simulate the space charge accumulation, but it cannot quantitatively relate the microscopic transport behaviours with the macroscopic conductivities of dielectrics. Considering the shortages of the above two models, an improved charge transport model, named carrier dynamic equilibrium model, was proposed in this study to simulate the polarisation process of the low-density polyethylene/ethylene propylene diene monomer bi-layer dielectric by introducing a source term of carrier dynamic equilibrium. Effects of carrier mobility and non-equilibrium carrier lifetime on the simulation results were explored, and a comparison among the results of measurement and different models was also made. Compared with the Maxwell–Wagner model and bipolar charge transport model, the improved model has the best coincidence with measurements, which can provide an accurate reference for the design of high-voltage direct current insulation systems.

Layered dielectric materials are currently in use for electric field stress control, but are limited by charge accumulation at the dielectric–dielectric interfaces. The current work uses micrometric particles to modify the effective permittivity of epoxy resin samples. Two broad kinds of samples are considered: discrete layered material (DLM) samples and functionally graded material (FGM) samples. DLM samples are obtained by bonding layers of epoxy resin with different filler loadings such that abrupt variation in permittivity might occur along the sample thickness. FGM specimens are prepared by hot pressing a comparatively large number of very thin layers of micro‐filled epoxy resin with very small differences in permittivity one over the other, thus creating a gradual spatial permittivity gradation. Dielectric properties of FGM and DLM specimens are compared in this study. Space charge accumulation is studied using the pulsed electroacoustic method; the accumulated charge density is seen to be lower in FGM. The uniformity of electric field distribution under applied electric stress is computed, and the field utilisation factor in FGM is seen to have a higher value. Also, the dissipation factor is lower and the short‐term breakdown strength is higher in FGM than in DLM samples, providing reason to prefer FGM for insulation to control electric stress. [ABSTRACT FROM AUTHOR]

Epoxy nano–micro composite specimen prepared with micro silica and ion trapping nanoparticle, by shear mixing process, was exposed to gamma radiation and its performance for space charge and charge trap characteristics were analysed. The threshold for space charge accumulation of epoxy nanocomposites reduces and rate of space charge accumulation increases with an increase in dosage of gamma irradiation. The average growth of space charge density during poling and charge decay rate during depoling are relatively higher for gamma-irradiated specimens than the virgin specimen. The initial surface potential has a marginal reduction with increase in the dosage of gamma radiation, but the surface potential decay rate has increased significantly. Trap distribution characteristics indicate more number of shallow traps and increase in charge mobility after irradiation. The relative permittivity and loss tangent of the specimens have high impact due to gamma irradiation. The activation energy calculated from DC conductivity by Arrhenius law reduces with increment in radiation dose. Laser-induced breakdown spectroscopy reflected no change in elemental composition with gamma-irradiated specimen. The variation in plasma temperature and ion line to atomic line intensity ratio with dosage of gamma radiation have direct correlation to the Vickers hardness number of the specimens.

The dielectric properties of oil-paper insulation degrade due to moisture ingression and ageing. This degradation significantly impacts the space charge accumulation and charge trapping behaviour in the insulation, which are vital parameters for insulation health under the high-voltage direct current environment. In this work, an improved model based on the isothermal relaxation current (IRC) has been developed to study the charge trapping behaviour of an oil pressboard under the influence of moisture and ageing. The conventional IRC model considers the total relaxation current because of charge de-trapping only. However, in the case of a composite dielectric like oil pressboard, dipolar relaxation also affects the relaxation current. In this work, a methodology has been proposed to investigate charge de-trapping behaviour of oil-pressboard insulation considering the dipole relaxation process from IRC measurements. For this purpose, frequency domain spectroscopy measurements and IRC measurements have been performed on oil-impregnated pressboard specimens carefully prepared in the laboratory having different ageing conditions and moisture contents. Results presented in this work depict that charge trapping parameters, i.e. the trap depth and trapped charge distribution are highly affected both by ageing and moisture. It was observed that ageing leads to the generation of deeper traps, while moisture mainly enhances the density of shallow traps.

This paper presents a numerical analysis of thermo‐electric fields of 10 and 35 kV AC XLPE cables in monopole, and tripole DC operating modes based on conduction current measurements. DC conductivities and electric field thresholds of the space charge accumulation for XLPE materials were estimated at different temperatures and electric fields. The result showed that the electric field threshold of the space charge accumulation for the materials reduced with an increase of the temperature. DC currents of the cables were increased with the increase of the operating temperatures in the three DC operation modes. The maximum DC operation voltage of the cables increased with the decline of the operation temperature in the three DC operation modes. The maximum transient electric fields were below the threshold of the space charge accumulation for the cables in the tripole DC operation. The maximum transmission power of the 10 kV XLPE cable in the DC operation modes was at 60° C, whereas the maximum transmission power of the 35 kV XLPE cable was at 50° C. It was elucidated that the 10 kV AC XLPE cable could have more advantages than the 35 kV AC XLPE cable in the three DC operation modes. [ABSTRACT FROM AUTHOR]

The semi-conductive layer located between the wire core and the insulation layer in high voltage direct current (HVDC) cable plays a vital role in uniform electric field and affecting space charges behaviors. In this work, the research idea of adding ionic conductive particles to semi-conductive materials to improve the conductive network and reduce the energy of the moving charge inside it and to suppress charge injection was proposed. Semi-conductive composites doped with different La0.8Sr0.2MnO3 (LSM) contents were prepared. Resistivity at different temperatures was measured to investigate the positive temperature coefficient (PTC) effect. Pulse electro-acoustic (PEA) method and thermal-stimulation depolarization currents (TSDC) tests of the insulation layers were carried out. From the results, space charge distribution and TSDC currents in the insulation samples were analyzed to evaluate the inhibitory effect on space charge injection. When LSM content is 6 wt. %, the experimental results show that the PTC effect of the specimen and charge injection are both being suppressed significantly. The maximum resistivity of it is decreased by 53.3% and the insulation sample has the smallest charge amount, 1.85 × 10−7 C under 10 kV/mm—decreased by 40%, 3.6 × 10−7 C under 20 kV/mm—decreased by 45%, and 6.42 × 10−7 C under 30 kV/mm—decreased by 26%. When the LSM content reaches 10 wt. %, the suppression effect on the PTC effect and the charge injection are both weakened, owing to the agglomeration of the conductive particles inside the composites which leads to the interface electric field distortion and results in charge injection enhancement.

Since the proposal of the notion of nanodielectric, the space charge characteristics of nanodielectrics have been widely investigated. With the addition of nanoparticles, some nanodielectrics exhibit smaller space charge accumulation amount during the polarisation, and also faster charge decay during the depolarisation, which is believed to be related to the interfacial layer between the nanoparticle and the base material. In this study, the space charge measurement methods, theoretical models, and experimental results are reviewed in detail. Space charge measurement methods have been greatly improved after more than 20 years development. The nature of the interfacial layer between the nanoparticle and the base material has been investigated in detail, and based on that, several models are proposed to explain some electrical experimental results of nanodielectrics. Furthermore, the parameters of nanoparticle (such as the type, size, amount, shape, and the surface modification), the experimental conditions, and the base material properties can strongly affect the space charge characteristics of nanodielectrics. This study will provide useful research results and conclusions for researchers, and may also be an overview for recent study and an outlook for future investigation on space charge characteristics of nanodielectrics.

Cross‐linked polyethylene (XLPE) insulation is successfully used for high‐voltage AC transmission. However, it is still under development for high‐voltage DC application due to space charge accumulation, which distorts the internal electrical field distribution and leads to its aging/failure. Therefore, the space charge should be measured and carefully analysed. On the other side, conductivity measurement helps to forecast the degradation probability of the insulation. Higher conductivity represents the severe degradation. Nanofiller addition, such as SiO2, TiO2, MgO and so on (<5 wt%), particularly surface‐modified nanofiller due to its better dispersion significantly suppresses the space charge accumulation and conductivity. Nevertheless, the choice of suitable nanofiller has still remained a challenge. With this context, space charge and conductivity of XLPE‐silica and XLPE‐magnesium oxide (MgO) surface‐modified nanocomposites are measured. This study proposes a parameter for nanofiller selection that will deliver optimal properties for the intended application. Results show that nanocomposites with higher nanofiller permittivity (i.e. MgO) have less space charge accumulation and low conductivity and are justified with the help of a band gap theory model. [ABSTRACT FROM AUTHOR]

For high voltage direct current (HVDC) cable, a semi-conductive layer lies between the conductor and the insulation layer; as the charge migrates the path from the conductor to the insulation material, it will affect space charge injection. In this work, the research idea of changing the injection path of moving charges within semi-conductive layer by magnetic particles was proposed. Semi-conductive composites with different SrFe12O19 contents of 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, and 30 wt.% were prepared, and the amount of injected charges in the insulation sample was characterized by space charge distribution, polarization current, and thermally-stimulated depolarization current. The experimental results show that a small amount of SrFe12O19 can significantly reduce charge injection in the insulation sample, owing to the deflection of the charge migration path, and only part of the electrons can enter the insulation sample. When the content is 5 wt.%, the insulation sample has the smallest charge amount, 0.89 × 10−7 C, decreasing by 37%, and the steady-state current is 6.01 × 10−10 A, decreasing by 22%. When SrFe12O19 content exceeds 10 wt.%, the charge suppression effect is not obvious and even leads to the increase of charge amount in the insulation sample, owing to the secondary injection of charges. Most moving charges will deflect towards the horizontal direction and cannot direct access to the insulation sample, resulting in a large number of charges accumulation in the semi-conductive layer. These charges will seriously enhance the interface electric field near the insulation sample, leading to the secondary injection of charges, which are easier to inject into the insulation sample.

Here, it is shown that by placing a thin film of N-CNTs on top of the transparent ITO hole collecting electrode of a polymer solar cell, the short circuit current density and efficiency are enhanced by 25 and 50%, respectively, and the usual efficiency losses in polymer solar cells as a function of incident light illumination intensity are significantly reduced. Nanostructuring the anode improves the mobility and collection of holes toward the anode, and as a result reduces space-charge accumulation in the polymer solar cell. [ABSTRACT FROM AUTHOR]

Studies on charge transport properties of space grade insulating materials become popular recently because it is closely related to the safe operation of spacecraft. Taking charge carriers retrapping and hole injection into consideration, we simulated the surface charging and the space charge accumulation properties of PTFE under lowenergy electron-beam irradiation using bipolar charge transport model in this paper. Parameters for simulation were based on experiments and previous studies. The secondary electron yields of PTFE irradiated by electron-beam of different primary electron energies were measured, and experimental data were fitted with an empirical equation. Thermally stimulated current was measured, and the trap parameters of PTFE were analyzed from the current-temperature curve by initial-rise method. In order to investigate the space charge distribution and the surface potential of steady state, factors like primary electron energy, sample thickness, temperature and trap density were selected as variables separately. It is found that the steady surface potential is nearly linear with the primary electron energy, which also fits the experimental results. The simulation results show the sample thickness affects the charging rate of surface potential mostly, and the charging rate is slower in thinner samples. The steady surface potential fluctuates slightly in the case that temperature is not high, but it increases significantly when temperature is higher than 400 K. With the increase in trap density, the space charge accumulation tends to focus on the surface and the dielectric/electrode interface, and the steady surface potential decreases. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Nonlinear optical microscopy maps electric fields in active organic photovoltaics. [•] Space charge accumulation is directly observed and quantified. [•] Slower charge carriers accumulate at greater concentrations. [ABSTRACT FROM AUTHOR]

Highlights: [•] Colloidal silica Layer-by-Layer assemblies have been deposited on polycarbonate. [•] These assemblies influenced the nature of the trapped space charges significantly. [•] Silica nanoparticles turned out to affect the resistance of polycarbonate to laser ablation. [ABSTRACT FROM AUTHOR]

New potential High Voltage Direct Current (HVDC) cable insulation materials based on nanocomposites are developed in this study. The nanocomposites are produced by blending of polypropylene (PP), propylene-ethylene copolymer (PP–HI) and a modified fumed silica (A-silica) in a concentration of 1 and 2 wt %. The A-silica is successfully modified with (3-aminopropyl)triethoxysilane (APTES) via a solvent-free method, as proven by infrared spectroscopy, thermogravimetry and transmission electron microscope mapping. A-silica in the polymer matrix acts as a nucleating agent resulting in an increase of the crystallization temperature of the polymers and a smaller crystal size. Moreover, the silica addition modified the crystals morphology of the unfilled PP/PP-HI blend. The composite containing A-silica with 2 wt% contains bigger-size silica clusters than the composite filled with 1 wt%. The composite with the higher A-silica concentration shows lower space charge accumulation and a lower charge current value. Besides, much deeper traps and lower trap density are observed in the composite with 2 wt% A-silica addition compared to the one with a lower concentration. Surprisingly, the presence of silica clusters with dimensions of more than 200 nm exhibit a positive effect on reducing the space charge accumulation. However, the real cause of this improvement might be due to change of the electron distribution stemming from the amine-amine hydrogen bond formation, or the change of the chain mobility due to the presence of occluded polymer macromolecules constrained inside the high structure silica clusters. Both phenomena may lead to a higher energetic barrier of charge de-trapping, thus increasing the depth of the charge traps. • Development of promising PP/PP-HI/APTES-silica nanocomposites for HVDC cable insulation application. • The modified silica clusters reduce the space charge accumulation of the nanocomposite, due to the deep trap formation.. • Presence of the deep traps might be attributed to the formation of occluded polymer chains or interactions between the silica nanoparticles, surface-modified by APTES. • Uniform deposition of APTES silane on the nanosilica surface by solvent-free modification. [ABSTRACT FROM AUTHOR]

The semi-conductive layer located between the wire core and the insulation layer in high voltage direct current (HVDC) cable plays a vital role in uniform electric field and affecting space charges behaviors. In this work, the research idea of adding ionic conductive particles to semi-conductive materials to improve the conductive network and reduce the energy of the moving charge inside it and to suppress charge injection was proposed. Semi-conductive composites doped with different La0.8Sr0.2MnO3 (LSM) contents were prepared. Resistivity at different temperatures was measured to investigate the positive temperature coefficient (PTC) effect. Pulse electro-acoustic (PEA) method and thermal-stimulation depolarization currents (TSDC) tests of the insulation layers were carried out. From the results, space charge distribution and TSDC currents in the insulation samples were analyzed to evaluate the inhibitory effect on space charge injection. When LSM content is 6 wt. %, the experimental results show that the PTC effect of the specimen and charge injection are both being suppressed significantly. The maximum resistivity of it is decreased by 53.3% and the insulation sample has the smallest charge amount, 1.85 × 10−7 C under 10 kV/mm—decreased by 40%, 3.6 × 10−7 C under 20 kV/mm—decreased by 45%, and 6.42 × 10−7 C under 30 kV/mm—decreased by 26%. When the LSM content reaches 10 wt. %, the suppression effect on the PTC effect and the charge injection are both weakened, owing to the agglomeration of the conductive particles inside the composites which leads to the interface electric field distortion and results in charge injection enhancement. [ABSTRACT FROM AUTHOR]

For high voltage direct current (HVDC) cable, a semi-conductive layer lies between the conductor and the insulation layer; as the charge migrates the path from the conductor to the insulation material, it will affect space charge injection. In this work, the research idea of changing the injection path of moving charges within semi-conductive layer by magnetic particles was proposed. Semi-conductive composites with different SrFe12O19 contents of 1 wt.%, 5 wt.%, 10 wt.%, 20 wt.%, and 30 wt.% were prepared, and the amount of injected charges in the insulation sample was characterized by space charge distribution, polarization current, and thermally-stimulated depolarization current. The experimental results show that a small amount of SrFe12O19 can significantly reduce charge injection in the insulation sample, owing to the deflection of the charge migration path, and only part of the electrons can enter the insulation sample. When the content is 5 wt.%, the insulation sample has the smallest charge amount, 0.89 × 10−7 C, decreasing by 37%, and the steady-state current is 6.01 × 10−10 A, decreasing by 22%. When SrFe12O19 content exceeds 10 wt.%, the charge suppression effect is not obvious and even leads to the increase of charge amount in the insulation sample, owing to the secondary injection of charges. Most moving charges will deflect towards the horizontal direction and cannot direct access to the insulation sample, resulting in a large number of charges accumulation in the semi-conductive layer. These charges will seriously enhance the interface electric field near the insulation sample, leading to the secondary injection of charges, which are easier to inject into the insulation sample. [ABSTRACT FROM AUTHOR]