Surface Charge Dissipation Research Articles

Electrical surface breakdown characteristics of micro- and nano-Al2O3 particle co-doped epoxy composites

Abstract Epoxy microcomposites are basic materials for gas-insulated switchgear (GIS) spacers that are subjected to huge electrical stress. Previous works have indicated that nanoparticles are beneficial to dielectric performance. However, surface electrical breakdown, a typical fault in GIS of co-doped micro- and nanoparticles in epoxy composites, is seldom studied. In this work, numerous concentrations of micro- and nano-Al2O3 are co-doped into an epoxy matrix; the surface traps, surface charging, and surface breakdown voltages (V sb) of the co-doped composites are studied, and the influence of micro- and nano-Al2O3 on the electrical surface breakdown is clarified. The results show that V sb first decreases and then increases with the microparticles, and V sb decreases from 25.34 kV to 19.52 kV. As the number of nanoparticles increases, V sb increases and then decreases when the microparticle loading is low, but decreases and then increases when the microparticle loading exceeds 40 wt%. Micro-Al2O3 particles introduce surface shallow traps into epoxy composites, while small amounts of nano-Al2O3 introduce deep traps. Two different mechanisms dominate the surface charging and V sb of epoxy micro-nanocomposites. When the surface conductivity is lower than 7 × 10−14 S, the surface charges are reduced by the suppression of electrode injection as the trap depth increases, and V sb increases. When the surface conductivity exceeds 7 × 10−14 S, the surface charge dissipation rate increases with the surface conductivity and V sb increases as the surface conductivity increases. Our work indicates that co-doped micro- and nano-particles should keep the surface conductivity away from the specic value (7 × 10−14 S) to safeguard insulation properties for GIS spacers.

Influence mechanisms of ultraviolet irradiation aging on DC surface discharge properties of silicone rubber in dry and humid air

In the modern DC electrical transmission system, high-energy photons interact with silicone rubber (SIR) chains during long-term ultraviolet (UV) irradiation, it degrades the surface properties and triggers surface discharge (flashover) along the SIR-air interface, threatening the secure operation of the advanced electrical equipment. To further comprehend how UV-aging influences the flashover performance, in this work, the chemical bonds, surface charge transport parameters, and flashover performance of UV-aged SIR samples are characterized, and the influence mechanisms of UV-aging on surface discharge in dry and humid air are comprehensively clarified through the investigation from “molecular-mesoscopic-macroscopic” scales. The results indicate both degradation and oxidization reactions occur during UV-aging. The degraded molecular chains dominate the discharge in dry air, while oxidization reactions determine the discharge in humid environment: The degradation reactions reduce the surface trap depth and increase surface conductivity, leading to large surface leakage current and surface charge dissipation rate, causing flashover voltage in dry air increases and decreases as UV-aging time increasing. The oxidization of the chains introduces –OH and –COOH groups into chains, enhancing permittivity and adsorbing H2O molecules, significantly increasing surface leakage current, causing surface discharge voltage in humid air to decrease as UV-aging time increases.

The mechanism of EP/SiC coating modulated DC flashover characteristics of epoxy composites in SF6/N2 mixtures

Surface flashover is an inevitable insulation issue for basin-type insulators in gas-insulated switchgears/lines, which significantly challenges the reliability of the electrical power systems. Previous studies have indicated that polymer/semiconductor-filler composite coatings effectively improve the insulation properties; however, the influence mechanism of the coating materials on flashover has not been demonstrated from a molecular perspective. In this work, epoxy/silicon-carbide (EP/SiC) composites were coated onto an EP substrate. The energy-level structure, surface trap, surface charging, and DC flashover voltage in SF6/N2 were calculated and characterized, and the process by which the tailored molecular energy level influences surface charge transport and flashover characteristics was elucidated. The incorporating of SiC particles reduced the width of the bandgap and introduced shallow traps, which improved carrier mobility and surface conductivity. Quantitative analysis of charge transport indicated that the improved carrier mobility and reduced surface trap level accelerated the surface charge dissipation. This reduced the tangential electrical field distortion and surface charge density and further impeded gas ionization. When the SiC concentration was 15 wt%, the flashover performance improved by 20.88%. This study describes the mechanism by which the EP/SiC coating regulates the surface charge distribution to improve the surface flashover performance by establishing a relationship among the microscopic molecular energy-level structures, mesoscopic charge transport, and macroscopic discharge phenomena.

Surface Charge Dissipation Characteristics of Al2O3/Silicone Rubber Composites with Different Weight Percentages

Surface Charge Dissipation Characteristics of Al₂O₃/Silicone Rubber Composites with Different Weight Percentages

Measuring gas discharge in contact electrification

Contact electrification in a gas medium is usually followed by partial surface charge dissipation caused by dielectric breakdown of the gas triggered during separation of the surfaces. It is widely assumed that such discharge obeys the classical Paschen’s law, which describes the general dependence of the breakdown voltage on the product of gas pressure and gap distance. However, quantification of this relationship in contact electrification involving insulators is impeded by challenges in nondestructive in situ measurement of the gap voltage. The present work implements an electrode-free strategy for capturing discrete discharge events by monitoring the gap voltage via Coulomb force, providing experimental evidence of Paschen curves governing nitrogen breakdown in silicone-acrylic and copper-nylon contact electrification. It offers an alternative approach for characterizing either the ionization energies of gases or the secondary-electron-emission properties of surfaces without the requirement of a power supply, which can potentially benefit applications ranging from the design of insulative materials to the development of triboelectric sensors and generators.

Suppression of dielectric surface flashover induced by strong electromagnetic field at multiple spatial scales based on above/sub-surface discharge development mechanisms

Spacecraft charging and electrostatic discharging (ESD) are prone to occur in harsh space environments. In particular, in the case of coupling strong electromagnetic field (EMF), ESD damages may occur at a low charging potential, posing a serious threat to on-orbit spacecraft missions. To investigate the mechanism and the pertinent suppression method for vacuum surface discharge induced by EMF, a specially-designed platform for EMF-induced surface discharge was set up. Surface structures with various spatial scales were created separately by using different surface engineering strategies, including direct fluorination, mechanical polishing, and 3D-printed grooving. The resulting surface physicochemical characteristics of the samples were examined. Furthermore, the surface discharge characteristics for different methods induced by strong EMF were systematically analyzed, considering the surface trap state distribution and secondary electron yield (SEY). The findings indicate that the proposed surface treatment methods demonstrate varying levels of improvement in mitigating EMF-induced discharge. Direct fluorination was found to produce lower SEY and to accelerate surface charge dissipation due to an elevated shallow trap density, making it favorable for suppressing the EMF-induced discharge. In addition, suitable surface roughness and groove size can effectively impede the development of the multipactor, thereby preventing EMF-induced discharge. This research is expected to provide valuable insights into the protection design of EMF-induced discharge on spacecraft.

Tailoring Organic/Inorganic Interface Trap States of Metal Oxide/Polyimide toward Improved Vacuum Surface Insulation.

High-voltage and high-power devices are indispensable in spacecraft for outer space explorations, whose operations require aerospace materials with adequate vacuum surface insulation performance. Despite persistent attempts to fabricate such materials, current efforts are restricted to trial-and-error methods and a universal design guideline is missing. The present work proposes to improve the vacuum surface insulation by tailoring the surface trap state density and energy level of the metal oxides with varied bandgaps, using coating on a polyimide (PI) substrate, aiming for a more systematical workflow for the insulation material design. First-principle calculations and trap diagnostics are employed to evaluate the material properties and reveal the interplay between trap states and the flashover threshold, supported by dedicated analyses of the flashover voltage, secondary electron emission (SEE) from insulators, and surface charging behaviors. Experimental results suggest that the coated PI (i.e., CuO@PI, SrO@PI, MgO@PI, and Al2O3@PI) can effectively increase the trap density and alter the trap energy levels. Elevated trap density is demonstrated to always yield lower SEE. In addition, increasing shallow trap density accelerates surface charge dissipation, which is favorable for improving surface insulation. CuO@PI exhibits the most remarkable increase in shallow trap density, and accordingly, the highest flashover voltage is 42.5% higher than that of pristine PI. This study reveals the critical role played by surface trap states in flashover mitigation and offers a novel strategy to optimize the surface insulation of materials.

Wet flashover voltage improvement of the ceramics with dielectric barrier discharge

Surface modification techniques with plasma are widely investigated to improve the surface insulation capability of polymers under dry conditions, while the relationship between treatment method, surface physical and chemical properties, and wet flashover voltage is still unclear for inorganic ceramics. In this work, the surface insulation properties of ceramics under wet conditions are improved using nanosecond-pulsed dielectric barrier discharge with polydimethylsiloxane (PDMS) as the precursor. The relationships between PDMS concentration and the water contact angle, dry and wet flashover voltages are obtained to acquire the optimal concentration. The surface charge dissipation test and surface physio-chemical property measurement with SEM, AFM, XPS are carried out to further explore the mechanism of surface insulation enhancement. The results show that film deposition with micron thickness and superhydrophobicity occurs at the PDMS concentration of 1.5%. The dry flashover voltage is increased by 14.6% due to the induction of deep traps, while the wet flashover voltage is increased by 66.7%. The gap between dry-wet flashover voltage is decreased by 62.3% compared with the untreated one due to the self-cleaning effect.

Plasticizer structural effect for sustainable and high-performance PVC gel-based triboelectric nanogenerators

A triboelectric nanogenerator (TENG) produces electrical energy by the accumulation of electric charges when two different materials rub against each other. In this study, the characteristics, and stabilities of adipate PVC gels with different adipate plasticizers were investigated for the development of triboelectric nanogenerators (TENGs) for sustainable energy harvesting. Various plasticizers with different numbers of carbon atoms in the alkyl chain were used to synthesize PVC gels, and their triboelectric properties, permittivities, and electrical conductivities were evaluated. In particular, we investigated the relationship between the surface charge dissipation rate and electrical resistivity of the PVC gel, which can maximize the TENG performance. The DOA5-based PVC gel TENG showed the highest output performance (198 V, 15.6 µA, and 384 µW/cm2) and stable output performance without plasticizer leakage for over 30 days at a high temperature. The developed TENG can be used as a power source for small electronic devices, maintaining a stable and high-output performance with high durability, making it ideal for self-powered systems in harsh environments requiring continuous power supply.

Improvement of surface insulating performance for polytetrafluoroethylene film by atmospheric pressure plasma deposition

The surface flashover phenomenon across a vacuum-dielectric interface severely limits the service life and operational reliability of high voltage electrical equipment. Surface modification by atmospheric pressure plasma treatment is a promising method to improve the surface insulating performance of polymers. In order to explore the mechanism of plasma processing on the vacuum flashover characteristics of polymer materials, atmospheric pressure plasma deposition was used to treat polytetrafluoroethylene (PTFE) film. The surface parameters under different processing conditions, such as surface chemical composition, surface resistivity, surface charge decay and trap distribution, were tested and analyzed. The space charge distribution of PTFE and the flashover voltage in vacuum were measured. The results show that Si–O–Si and Si–OH groups are introduced on the surface of PTFE, and the characteristic peaks of PTFE are gradually weakened with the increase of processing time. The surface trap density increases and more traps with lower energy level arise with longer processing time. The plasma deposition changes the space charge distribution in PTFE body, and leads to positive charge accumulation inside the sample. The flashover field strength respectively increases by 15% and 70% in direct current (DC) voltage and microsecond pulse voltage after plasma deposition. The rapid dissipation of surface charge is the main reason for pulse flashover voltage enhancement, while the increase of surface leakage current due to lower surface resistivity and space charge accumulation in PTFE body make the DC flashover voltage reach the saturation point. Therefore the surface insulating and body performance of polymer materials after plasma modification processing should be considered comprehensively based on different applications.

Methyl and carbon–carbon double bond in anhydride molecules modulated surface charge trap depth of epoxy materials

Epoxy insulators in gas insulated switchgear and gas insulated transmission lines tend to accumulate surface charges, leading to insulation flashover. Improving the surface trap characteristics of epoxy materials, which can accelerate the surface charge dissipation of epoxy insulators, is a promising method to improve the surface insulation performance. The surface trap characteristics of epoxy materials are strongly influenced by the chemical groups in the acid anhydride molecules. In this work, by quantum chemical calculations and isothermal surface potential decay tests, taking six organic anhydrides that differ only in the methyl and carbon–carbon double bonds, we find the modulation laws of methyl and carbon–carbon double bonds on the charge trap depth within and between molecular chains. The regulation mechanism is revealed from the microscopic perspectives of electron energy structure and electron cloud offset. The changes of surface charge trap depth of epoxy materials are primarily attributed to the changes in the spatial distribution of the electron cloud density between and on the valence bonds caused by the interaction between the electron-donating methyl group and the electron-absorbing carbon–carbon double bond.

Surface Flashover Characteristics of Epoxy Resin Under DC Voltage and its Modification Method

Epoxy resin is used as insulating material in electrical equipment due to its perfect electrical, mechanical and thermal properties. The accumulation of charge on the surface of the material and its promotion of surface flashover, however, often lead to insulation failure and directly endanger the operation of electrical equipment safety. Therefore, improving the insulation performance of epoxy materials is of great significance for protecting high-voltage power equipment. In this paper, a blend-modified epoxy resin was synthesized by DGEBA and DCPDE, and its surface charge dissipation and surface flashover characteristics with DC voltage were tested. The experimental results show that the surface charge distribution can be effectively changed by changing the ratio of epoxy resin, which is meanful to improve the material’s insulation properties.

All-organic modification coating prepared with large-scale atmospheric-pressure plasma for mitigating surface charge accumulation

The surface charge accumulation on polymers often leads to surface flashover. Current solutions are mainly based on the introduction of inorganic fillers. The high-cost process and low compatibility remain formidable challenges. Moreover, existing researches on all-organic insulation focus on capturing electrons, contrary to alleviating charge accumulation. Here, an all-organic modification coating was prepared on polystyrene (PS) with the large-scale atmospheric-pressure plasma, which exhibits outperformed function in mitigating surface charge accumulation. The surface charge dissipation rate and surface conductivity are promoted by about 1.37 and 9.45 times, respectively. Simulation and experimental results show that this all-organic modification coating has a smaller electron affinity potential compared with PS. The decrease of electron affinity potential may result in accelerated surface charge decay of PS, which has never been involved in previous works. Moreover, this coating also has good reliability in a repeated surface flashover. This facile and large-scale approach brings up a novel idea for surface charge regulation and the manufacture of advanced dielectric polymers.

Optimization of Carbon Nanotube Doping on Nonlinear Conductivity, Surface Charge Dissipation and Electric Field Regulation of SiC/SR Composites Insulators Subjected to DC High Voltages

Adaptive material can alleviate the local high electric field in electrical devices, due to its nonlinear conductivity characteristics. To solve the deterioration problem caused by the high doping of large-diameter fillers in adaptive material, CNT (carbon nanotube) was used as the second filler. And the effect of CNT doping amount on the conductivity of SiC/SR (silicone rubber) composites was explored. Experiments showed that CNT doping can improve the nonlinear conductivity. The threshold field of the material doped with 0.7 vol % CNT decreased by 97%, and the nonlinear coefficient was increased by 83.7%. With the increase of CNT doping content, the decay rate of surface potential increased, which was attributed to the increase of the carrier mobility and ratio of shallow-to-deep trap density. A new field grading material (FGM) coating structure was proposed, which was compared with the traditional structure. Through finite element simulation, the field grading effect of the two structures can be analyzed. The results showed that, the field grading effects of the two coating structures were almost the same. But considering the influence of surface charge dissipation, the new coating structure was selected. The electric field of insulator surface and interface can be reduced by more than 30% with the best CNT doping ratio. It was verified that, the interface charge and leakage current of the insulator coated with the best FGM were at the compliance level.

Enhanced Aramid/Al2O3 interfacial properties by PDDA modification for the preparation of composite insulating paper

To further improve the electrical insulation properties of meta-aramid paper, polydimethyldiallyl ammonium chloride (PDDA) was used for the modification of nano-Al2O3 in this work. The modified products were characterized by means of transmission electron microscopy, Fourier transform infrared spectrometer and liquid Zeta potential. The original and PDDA-modified nano-Al2O3 was doped into the aramid fiber composite, and the effects of PDDA and filler mass fraction on several properties such as electrical conductivity, breakdown strength and surface charge dissipation rate of insulating paper were studied. Finally, the interfacial properties of the composites were investigated using molecular dynamics. The results showed that PDDA was successfully coated on the surface of nano-Al2O3, and its surface potential was changed from negative to positive, which could improve the interface characteristics between filler and matrix and enhance the dielectric strength of aramid paper. Besides, saturation effect of PDDA modification was observed, and when the amount of PDDA was 10% and the content of modified nano-Al2O3 was 3%, the breakdown strength of aramid paper was increased by 20%, and the volume conductivity was decreased by 68%. The simulation result revealed that PDDA could improve the insulation performance of aramid paper by reducing the interfacial binding energy between aramid and filler.

Improving surface performance of silicone rubber for composite insulators by multifunctional Nano-coating

Composite insulator is an important component of outdoor insulation systems. It works in complex environments and faces a series of problems such as surface contamination, loss of hydrophobicity, and accumulation of surface charges, which may eventually lead to flashover. Aiming to solve these problems in a simple and scalable method, we propose a multifunctional nano-coating based on SiO2/PDMS/EP. By the combination of multiscale structure and low surface energy modification, this coating shows excellent water-repellency performance, a large contact angle greater than 160° and a small rolling angle near 0° are achieved on coated silicone rubber, which enables the surface with excellent self-cleaning performance. Benefiting from the multiscale roughness, the heat transfer is inhibited by the reduced contact area, which further slows down the icing process on coated silicone rubber. The de-icing force on coated silicone rubber is also smaller than that on pristine silicone rubber. This coating also introduces many shallow traps to the surface, which is beneficial to the fast surface charge dissipation in a short time. Besides, the high water-repelling ability can promote the droplet to roll away under the action of electrical field force, which alleviates the electrical distortion caused by the droplets. As a result, the wet flashover voltage of coated silicone rubber is 60% higher than that of pristine silicone rubber. This multifunctional coating is a facile, scalable, and effective approach to improving the comprehensive surface performance of insulators.

Influence of SiC/Epoxy Coating on Surface Charging Phenomenon at DC Voltage—Part II: Charge Dissipation

In this article, the dissipation of predeposited surface charges on the SiC/epoxy coated insulator is investigated. Similar to Part I of this study, the analysis is carried out for the system of a pair of finger-shaped metallic electrodes placed on flat material samples and different types of material precharging are considered. Specifically, two cases based on different types of electrode–sample contacts (Cases 1 and 2, similar to Part I) are examined as well as surface charging by external corona (Case 3). It is shown that surface charge dissipation in Cases 1 and 2 takes place in two stages, whereas three stages in the charge decay process are identified in Case 3. It is shown that the rate of charge dissipation is strongly affected by the increase of the content of SiC filler in the coating material. The experimental results obtained for different cases are compared and discussed by employing results of the calculations of the electric field in the experimental setups and surface conductivities and surface trap characteristics obtained in Part I.

Improving the charge dissipating performance and breakdown strength of epoxy resin by incorporating polydopamine-coated barium titanate

Incorporating inorganic filler is an efficient method to improve the surface charge dissipating performance of epoxy resin (EP), and the key is to strengthen the interfacial interaction between EP matrix and filler. In this work, the polydopamine (PDA) coated barium titanate (BT) was synthesized via commonly used in situ self-polymerization of dopamine in BT aqueous suspension, and then BT-PDA particles were introduced into EP matrix to prepare EP/BT-PDA composites. The introduction of PDA coating on the BT surfaces was able to strengthen the interfacial filler-matrix interactions, significantly improving the dispersion of BT-PDA particles in the EP/BT-PDA composites. As a result, the surface charge dissipation was effectively enhanced for the EP/BT-PDA composites, as the EP composite filled with 1.0 wt% BT-PDA exhibited the surface potential decreasing rate around twice as fast as that of pure EP.

Penetration of plasma jet into porous dielectric layer: confirmed by surface charge dissipation of silicone rubber

The penetration of plasma in the porous structure is important for its application in plasma catalysis, plasma medicine, etc. In this paper, the penetration of plasma species in the porous kaolin layer was investigated. The silicone rubber was chosen as a probe and the inorganic porous dielectric layer was constructed with granular kaolin coated on the surface of silicone rubber. AC and pulsed plasma jets were applied to the silicone rubber, and the surface charge dissipation of bulk silicone rubber was measured to characterize the changes of surface property caused by the plasma penetration. The results showed that plasma could penetrate the porous dielectric layer on the silicone rubber and interact with the surface of silicone rubber, thus accelerating the surface charge dissipation of the bulk silicone rubber. The increase of shallow traps and surface conductivity after plasma treatment was the main reason for the acceleration of surface charge dissipation. The surface charge dissipation is enhanced with the increase of treatment time and the generating voltage of plasma. The surface charge dissipation declined for silicone rubber with a thicker kaolin layer due to the blocking of the kaolin layer on the interaction of plasma and the silicone rubber. For the same kind of plasma, the charge dissipation rate was linearly related to plasma dose which was represented by the energy density of plasma applied on the coated silicone rubber. At the same energy density, the surface charge dissipation of silicone rubber after pulsed plasma treatment was faster than that of AC plasma.

Synergetic optimization of charge transport and breakdown strength of epoxy nanocomposites: Realizing sandwich topological structure through constructing a SiC@SiO2/EP surface layer and m-BNNS/EP insert layer

Polymeric materials doped with wide-bandgap semiconductors exhibit intriguing nonlinear conductivity and rapid charge dissipation characteristics. However, excessive doping to accelerate charge dissipation occurs at the expense of breakdown strength. In this work, a sandwich topological structure is proposed to realize synergetic optimization of charge transport and breakdown strength. SiC nanoparticles decorated with insulation shell SiO2 were prepared, which served as fillers in the two surface layers of sandwich structured epoxy composites with exfoliated and functionalized m-BNNS doped into epoxy as the insert layer. The significantly improved breakdown strength approaches 65.8 kV/mm (44% higher than pristine epoxy resin) for sandwich structured composites due to local electric field redistribution while maintaining excellent charge dissipation ability owing to surface charge dissipation and charge decay along the bulk. Moreover, the dielectric loss still retains a low value of 0.02. These novel sandwich structured composites present promising potential in electrical and electronic insulation systems.