Charge Dissipation Rate Research Articles

Electrical Response of Different Crystalline Microregions in Poly(vinylidene fluoride).

The crystal structure has a great influence on the dielectric and piezoelectric performance of poly(vinylidene fluoride) (PVDF). In this work, we prepared PVDF films with two typical crystalline phases (α and β). In situ Kelvin probe force microscopy (KPFM) and Piezoelectric force microscopy (PFM) were employed to investigate the responses of different PVDF crystalline phases to charge mobility, polarization, and piezoelectric properties. We used a homemade Kelvin probe force microscope (KPFM) to inject charges into the two crystalline phases to investigate the differences in the response of different crystalline phases of PVDF to electrical excitation on a microscopic scale. It was found that the α-phase has a lower charge injection barrier and is more susceptible to charge injection and that the α-phase is accompanied by a faster charge dissipation rate, which makes it easier to accumulate charge at the interface between the α-phase and β-phase PVDF. Moreover, the PFM polarization manipulation showed no change in the amplitude and phase diagram of the α-phase under ±10 V bias. In contrast, the β-phase showed a clear polarization reversal phenomenon and a significant increase in piezoelectric amplitude, which is consistent with its polar intrinsic properties. This study provides valuable insights into the multiphase contributions and a reference for designing advanced PVDF dielectrics.

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.

Revamping Triboelectric Output by Deep Trap Construction.

High output performance is critical for building triboelectric nanogenerators (TENGs) for future multifunctional applications. Unfortunately, the high triboelectric charge dissipation rate has a significant negativeimpact on its electrical output performance. Herein, a newtribolayer is designed through introducing self-assembled molecules with large energy gaps on commercial PET fibric toform carrier deep traps, which improve charge retention while decreasing dissipation rates. The deep trap density of the PET increases by two orders of magnitude, resulting in an 86% reduction in the rate of charge dissipation and a significant increase in the charge density that can be accumulated on tribolayer during physical contact. The key explanation is that increasing the density of deep traps improves the dielectric's ability to store charges, making it more difficult for the triboelectric charges trapped by the tribolayer to escape from the deep traps, lowering the rate of charge dissipation. This TENG has a 1300% increase in output power density as a result of altering the deep trap density, demonstrating a significant improvement. This work describes a simple yetefficient method for building TENGs withultra-high electrical output and promotes their practical implementation in the sphere of the Internet of Things.

Study on interface insulation properties of Al2O3 epoxy composites using plasma jet‐fluorinated etching/SiOx deposition

AbstractDue to their superior mechanical and electrical characteristics, Al2O3 epoxy composites (Al2O3/EP) are extensively utilized in producing insulation devices. However, Al2O3/EP is prone to accumulating a large amount of charge under a direct current (DC), which threatens the operation of the power system. In this article, we conducted surface fluorinated etching and SiOx deposition on the material by atmospheric pressure plasma jet (APPJ). Various testing methods were used to investigate the impacts of plasma modification on the physicochemical characterization of Al2O3/EP, and the changes in superficial conductivity, flashover voltage, charge dissipation rate, and trap distribution were experimentally tested. The influences of two plasma modification methods on the physicochemical characterization of Al2O3/EP were analyzed. The enhancement mechanism of Al2O3/EP flash behavior by fluorinated etching and SiOx deposition is summarized. The findings demonstrate that the insulation behavior of Al2O3/EP results from a combination of a few dominant and multiple factors. Fluorinated etching enhances the degree of roughness and the relative proportion of the F element, provides chemically deep traps, and raises the flashover voltage by up to 19%. SiOx deposition boosts the dispersion of charges by forming SiOx layers on the surface, reducing the degree of roughness and increasing the content of the silicon–oxygen element, making it more difficult for charges to accumulate and increasing the flashover voltage by up to 15%. This study will reveal the internal relationship between gas–solid interface and surface flashover, and provide a possible scheme for suppressing surface flashover.Highlights Modifications substantially increase the flashover voltage. Modifications allow a wide range of interface parameters to be adjusted. The effects of modifications on physicochemical properties are compared. The enhancement mechanism of flashover voltage by modifications is compared. The overall effect of multiple factors on insulation properties is analyzed.

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.

Laboratory investigations of triboelectric charging of dust by rover wheels

The dusty plasma environments of airless bodies present challenges for both exploration and science missions to their surfaces. Objects moving on the surface, such as rover wheels, transfer charges onto regolith dust due to the triboelectric effect. The charged dust particles can readily stick to spacesuits as well as the optical, electronic, and mechanical components of equipment and instruments, causing their degradation. This effect is more pronounced in permanently shadowed regions (PSRs) of the Moon, where the charge dissipation rate is low due to a lack of ambient plasma. Here we report the first results of an experimental investigation of the tribocharging effect between dust and rover wheels. Various wheel surface materials along the triboelectric series are selected. The effects of varying wheel speeds and dust types are explored. Results indicate that charge distributions conform to the triboelectric properties of the dust and material it comes into contact with. High charges of up to ∼2 pC are measured on dust grains ∼100 μm in diameter, which is equivalent to a surface potential of few hundred volts. Results also suggest that higher wheel speeds may result in more dust-dust interactions, changing the charging behavior of the dust grains. These findings indicate a need for future studies to better understand tribocharging in various exploration scenarios in order to design effective dust mitigation strategies and methods.

Nanocavities stabilize charge: Surface topology is a general strategy for controlling charge dissipation

Strategies for controlling static charge on surfaces have always focused on charge generation. On the other hand, charge dissipation also plays a very important role in most current technologies: the rate of charge dissipation critically needs to be much slower for applications and much faster for eliminating the many undesirable effects of static charge in industry. Controlling charge dissipation is extremely difficult as it involves a gas-phase chemical reaction (i.e., ionization of gaseous molecules). This study reports for the first time that surface topology effectively controls charge dissipation. Charge dissipation is much slower for rough surfaces and much faster for smooth surfaces. The effect is great: a rough surface retains a remarkable 100 times more charge than a smooth surface during dissipation. This difference gives rise to a large difference in power produced by triboelectric generators by 104 times. This phenomenon is thus the much-needed solution for retaining charge for useful applications or eliminating charge to prevent the undesirable effects of static charge from occurring. Surface topology is a physical property, whereas ionization is a chemical reaction; thus, it is surprising that surface topology affects reaction. Static charge is found to correlate spatially with the nanoscale valleys of the rough surface. Therefore, the high curvature provided by the nanocavities of rough surfaces is the fundamental physical principle for stabilizing ions via dipole interactions with surface molecules and reducing ionization. Varying surface topology is thus an effective and simple strategy for either increasing or decreasing charge dissipation (e.g., for triboelectric power generator and electrostatic self-assembly).

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.

Interfacial Insight of Charge Transport in BaTiO3/Epoxy Composites.

Space charge accumulation greatly influences the dielectric performance of epoxy composites under high voltage. It has been reported that nano-fillers can suppress the charge accumulation in the bulk of insulation materials. However, it is still unclear how the nano-fillers influence the charge distribution at the interface between the filler and polymeric matrix. In this work, the dielectric properties and the local dynamic charge mobility behavior at the interface of barium titanate/epoxy resin (BTO/EP) composites were investigated from both bulk and local perspectives based on the macroscopic test techniques and in-situ Kelvin probe force microscopy (KPFM) methods. Charge injection and dissipation behavior exhibited significant discrepancies at different interfaces. The interface between BTO and epoxy is easy to accumulates a negative charge, and nanoscale BTO (n-BTO) particles introduces deeper traps than microscale BTO (m-BTO) to inhibit charge migration. Under the same bias condition, the carriers are more likely to accumulate near the n-BTO than the m-BTO particles. The charge dissipation rate at the interface region in m-BTO/EP is about one order of magnitude higher than that of n-BTO/EP. This work offers experimental support for understanding the mechanism of charge transport in dielectric composites.

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.

Peak-type charge barriers enabling high surface-insulating performance of epoxy composites

The rapid increase in electrical and electronic devices integration necessitates the urgent development of epoxy composites with more reliable surface-insulating performance. Charge traps with valley-like features are known to improve the surface-insulating characteristics of insulating materials. Inspired by this strategy, a new approach is reported herein for constructing peak-type charge barriers to enhance the surface-insulating performance of epoxy composites. This paper describes the construction of 0.92 eV peak-type charge barriers on the surface of an epoxy composite by doping with nanodiamonds (NDs), which have a negative electron affinity. The constructed barriers alter the charge migration behavior on the surface of the ND/epoxy composite. Consequently, the charge dissipation rate and surface flashover voltage of the ND/epoxy composite increase by 563% and 17.6%, respectively. Additionally, the NDs improve the arc resistance duration of the epoxy resin by 211%, owing to their electron-emitting effect under strong electrical fields. This strategy, by which the peak-type charge barriers constructed using the NDs exhibit excellent surface-insulating characteristics to the epoxy composites, can be adopted as a new approach to improve the surface-insulating abilities of materials.

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.

DC Surface Flashover Characteristics of Polyimide Containing Polyhedral Oligomeric Silsesquioxane (POSS) in the Main Chains under Vacuum.

Polyimide, which is widely used to insulate power equipment operating in a vacuum environment, is prone to insulation failure due to surface flashover. Using POSS to modify it is an effective solution. This paper focuses on the study of DC surface flashover characteristics in vacuum of POSS/polyimide composite film, by introducing 1%, 3%, 5% equivalent mole content of POSS into polyimide, and conducting a surface flashover characteristics test in vacuum together with pure polyimide. The physical and chemical properties of the composite films were tested utilizing Fourier transform infrared spectroscopy and ultraviolet–visible spectroscopy. Combined with resistivity, SEM, and other test techniques, the influence mechanism of POSS molecular modification on DC surface flashover characteristics of polyimide films in vacuum was initially revealed. The results showed that after the introduction of POSS, the overall functional group structure of polyimide remained unchanged, the intermolecular charge transfer complexation was inhibited, and the transmittance of the film increased. The thermal conductivity and thermogravimetric temperature of the film are improved to a certain extent, and the mechanical properties are slightly decreased. With the increase of the introduced POSS content, the dielectric strength of the composite film is also enhanced. The surface flashover voltage of the composite film with a POSS content of 5% is 17.5 kV in vacuum, which is 30.5% higher than that of the pure film. Further analysis shows that the introduction of POSS will reduce the resistivity of the composite film, accelerate the dissipation of surface charges, and increase the flashover voltage. In addition, POSS forms a uniformly distributed Si-O-Si cage-like structure through molecular modification. When the surface of the film is damaged, SiOx inorganic flocculent particles are generated, which can not only scatter electrons, but also shallow the depth of trap energy level and accelerate the dissipation rate of surface charge, thus increasing the flashover voltage.

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.

Effect of Bismuth Ferrite Nanometer Filler Element Doping on the Surface Insulation Properties of Epoxy Resin Composites.

In the direct current electric field, the surface of epoxy resin (EP) insulating material is prone to charge accumulation, which leads to electric field distortion and damages the overall insulation of the equipment. Nano-doping is an effective method to improve the surface insulation strength and DC flashover voltage of epoxy resin composites. In this study, pure bismuth ferrite nanoparticles (BFO), as well as BFO nanofillers, which were doped by La element, Cr element as well as co-doped by La + Cr element, were prepared by the sol-gel method. Epoxy composites with various filler concentrations were prepared by blending nano-fillers with epoxy resin. The morphology and crystal structure of the filler were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) tests. The effects of different filler types and filler mass fraction on the surface flashover voltage, charge dissipation rate, and trap characteristics of epoxy resin composites were studied. The results showed that element doping with bismuth ferrite nanofillers could further increase the flash voltage of the composites. The flashover voltage of La + Cr elements co-doped composites with the filler mass fraction of 4 wt% was 45.2% higher than that of pure epoxy resin. Through data comparison, it is found that the surface charge dissipation rate is not the only determinant of the flashover voltage. Appropriately reducing the surface charge dissipation rate of epoxy resin composites can increase the flashover voltage. Finally, combining with the distribution characteristics of the traps on the surface of the materials to explain the mechanism, it is found that the doping of La element and Cr element can increase the energy level depth and density of the deep traps of the composite materials, which can effectively improve the flashover voltage along the surface of the epoxy resin.

Thermal‐aging characteristics of epoxy/glass fiber composite materials for dry‐type air‐core reactors

AbstractIn recent years, dry‐type air‐core reactors have frequently experienced inter‐turn short circuits due to the aging of the inter‐turn insulation. In this paper, we prepared epoxy/glass fiber samples and carried out an accelerated thermal aging test up to 840 hours. In different stages of aging, we tested the surface insulation properties, dielectric properties, thermal and mechanical properties of the samples. The results show that: Flashover voltage drops significantly, and when aging for 35 days, it has dropped by 12.4%. This is because aging is accompanied by the conversion of shallow traps to deep traps and the reduction of conductive channels, which slows down the charge dissipation rate and decreases the flashover voltage. Dielectric, thermal, and mechanical properties also show a deteriorating trend. Through the analysis of the changes in thermal and mechanical properties, it is inferred that thermal aging will damage the epoxy matrix more than the glass fiber. In addition, combined with the scanning electron microscope, Fourier transform infrared spectrometer, and X‐ray photoelectron spectrometer characterization results, we believed that the main reason for the material deterioration is the detachment of the glass fiber and the break of the long chain of the matrix. This article has certain reference value for the subsequent engineering application and online monitoring of this material.

Research on corona discharge suppression of high-voltage direct-current transmission lines based on dielectric-film-covered conductor

Corona discharge suppression for high-voltage direct-current (HVDC) transmission lines at line terminals such as converter stations is a subject that requires attention. In this paper, a method based on a conductor covered with dielectric film is proposed and implemented through a bench-scale setup. Compared with the bare conductor, the corona discharge suppression effect of the dielectric-film-covered conductor under positive polarity is studied from the composite field strength and ion current density using a line-plate experimental device. The influences of film thickness and film material on the corona discharge suppression effect are investigated. The charge accumulation and dissipation characteristics of different film materials are also studied. The results show that the conductor covered with dielectric film has excellent ability to inhibit corona discharge. The ground-level composite field strength of the conductor covered with dielectric film is lower than its nominal field strength, and its ion current density is at the nA m−2 level. The corona threshold voltage can be promoted by increasing the film thickness, but the ability to inhibit corona discharge becomes weak. The larger the surface electric field strength, the more charge accumulated, but the faster the charge dissipation rate. Compared with polyvinyl chloride film, cross-linked polyethylene film has stronger charge accumulation ability and slower charge dissipation rate, which can better restrain the corona discharge of HVDC transmission lines.

Low-temperature plasma polymerized fluorocarbon coating promotes surface charge dissipation in polystyrene

Polystyrene (PS) is a common insulating material in pulsed power devices, which has excellent and reliable insulation properties. However, the charge accumulation on the insulator surface seriously threatens its surface insulation property. Surface modification has been verified as an effective way for inhibiting surface charge accumulation. In this paper, plasma polymerized fluorocarbon (PPFC) coating was prepared by low-temperature plasma polymerization in the mixture of methyl-methacrylate and dodecafluoroheptyl-methacrylate (DFHMA). Compared with the untreated PS, the surface charge dissipation rate of PPFC coating is increased by more than 6 times. The introduction of DFHMA makes the coating have no obvious ageing effect after the storage, and has good reusability after the surface flashover. This work provides a new method for modification of polymer dielectrics and a novel way for the preparation of high-charge-dissipation polymers in other related fields.

Fluorinated SnO2/ER as an antistatic coating for enhancing the surface insulating strength of epoxy insulators

AbstractThe surface coating of epoxy resin has been widely used in the composite materials with micron scale fillers, but the related research on the composite coating filled with nanoparticles is still rare. SnO2 is a common antistatic additive in composite materials, and it is also a semiconductor material, capable of uniform voltage. In this paper, nano‐SnO2 powder was considered as the filler of coating materials. By analyzing the microscopic test results, the flashover voltage, surface charge dissipation, and surface conductivity of the coating sample, the effects of coating treatment and nano‐SnO2 fluorination on the surface insulation properties of epoxy insulators were studied. It is found that the flashover voltage and surface charge dissipation rate of the coating sample can be improved by both coating treatment and fluorination treatment, thus improving the surface insulation performance of epoxy insulators. The modification process and test results have guiding significance for improving the surface insulation performance of epoxy insulators.