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The interactions between molecules and electrode surfaces play a key role in electrochemical processes and are a subject of extensive research, both experimental and theoretical. In this paper, we address the water dissociation reaction on a Pd(111) electrode surface, modeled as a slab embedded in an external electric field. We aim at unraveling the relationship between surface charge and zero-point energy in aiding or hindering this reaction. We calculate the energy barriers with dispersion-corrected density-functional theory and an efficient parallel implementation of the nudged-elastic-band method. We show that the lowest dissociation barrier and consequently the highest reaction rate take place when the field reaches a strength where two different geometries of the water molecule in the reactant state are equally stable. The zero-point energy contributions to this reaction, on the other hand, remain nearly constant across a wide range of electric field strengths, despite significant changes in the reactant state. Interestingly, we show that the application of electric fields that induce a negative charge on the surface can make nuclear tunneling more significant for these reactions. [ABSTRACT FROM AUTHOR]

Charge accumulation on the surface of insulation dielectric used in high voltage DC equipment is one of the important causes of surface flashover. Surface charge accumulation is closely related to surface trap characteristics. In this paper, the surface trap energy level distribution of polyimide (PI) was calculated and analyzed by the corona charging method and surface potential decay method. Besides, electron and hole trap characteristics were studied by changing the polarity and amplitude of the charging voltage. Furthermore, the influence of surface charge polarity and quantity on the flashover voltage was researched. Experimental results indicate that the energy level of traps corresponding to the maximum trapped charge density ranges around 0.94 eV. In addition, the energy level of the hole trap is slightly higher than that of the electron trap. The maximum charge density captured by the electron trap and hole trap is about 1.17 × 1021 and 1.03 × 1021 eV−1 m−3, respectively. The polarity of the surface charge can influence the conductivity characteristics of PI, the surface heterocharge reduces the volume conductivity by about 80% while the surface homocharge improves the volume conductivity of PI by about 6.4 times. Besides, both negative and positive surface charges can improve surface conductivity. The polarity of surface charge influences the flashover characteristics of PI, the flashover voltage increases by about 37.8% with the increase of homocharge density and decreases by about 23.8% with the increase of heterocharge density, which is related to the change of electric field near the cathode caused by surface charge accumulation. [ABSTRACT FROM AUTHOR]

The proliferation of urbanization and the integration of new energy sources have stimulated the development of gas-insulated transmission lines and switchgear (GIL/GIS). In particular, the compact DC GIS in offshore converter platforms will significantly reduce footprints for DC switchyards, exhibit exceptional climatic resistance, and facilitate the cost-effective connection of remote offshore wind farms and submarine links. Nevertheless, insulators used in GIS/GIL always suffer from surface charge accumulation under DC stress, which could distort and enhance the local electric field and thus trigger a flashover at the gas–solid interface if it exceeds certain magnitude levels. This susceptibility becomes a major concern affecting the reliability of DC gas-insulated systems. Beyond these engineering-related challenges lie fundamental physics problems involving mechanisms of charge accumulation and charge-induced flashover which still require exploration. To this end, this paper presents an overview of recent advancements on this topic whilst highlighting relevant issues to be addressed. Specifically, the surface charge accumulation phenomena under DC fields are reviewed, and the charging mechanisms are summarized from macroscopic to microscopic perspectives. Further, the correlation between surface charge and surface flashover is discussed. Moreover, recent developments in tailoring methods for surface charging are also presented. Finally, perspectives are given on current research progress and future needs. [ABSTRACT FROM AUTHOR]

The tribovoltaic effect raises an emerging semiconductor energy technology and silicon‐based tribovoltaic nanogenerator (Si‐TVNG) has aroused great attentions. However, the electrical output of Si‐TVNG is extremely unstable due to its complicated mechanism. Here, a competitive mechanism between the built‐in electric field (BEF) and the interfacial electric field (IEF) is proposed to determine the current direction and magnitude of the Si‐TVNG. The results indicate that the natural oxide layer, load pressure, and resistivity of Si significantly affect the IEF and BEF. The natural oxide layer can store surface charges by contact electrification, resulting in a IEF dominant carriers transport process. Conversely, lower resistivity and higher load pressure can reduce the contact resistance, thereby decreasing the surface charges caused by contact electrification and leading to a BEF dominant carrier transport process. This work contributes to deeper understandings of the tribovoltaic effect and further clarifies the theoretical mechanisms of carrier excitation and directional transport. [ABSTRACT FROM AUTHOR]

This study investigates the surface charging and electrophoretic motion of polyethylene glycol-rich (PEG-rich) micro-droplets in dextran-rich solutions or dextran-rich micro-droplets in PEG-rich solutions. The electrophoretic velocities of the droplets were measured in a centimeter-sized chamber under an optical microscope. It was found that the direction of electrophoretic motion of both the PEG-rich droplets and dextran-rich droplets is opposite to the applied electric field, meaning that both the PEG-rich droplets and dextran-rich droplets are negatively charged. The electrophoretic velocity is independent of droplet size but proportional to the electric field strength. Increasing the NaCl concentration reduces the electrophoretic velocity of PEG-rich droplets and increases it for dextran-rich droplets, suggesting different surface charge changes due to ion affinity. The charge densities and velocities are affected by the PEG and dextran mass fractions. Physical models for droplet surface charging under different conditions were proposed to explain the experimental results. [ABSTRACT FROM AUTHOR]

Herein, the surface charge characteristics of a tri‐post insulator in a ± 500 kV direct current gas‐insulated transmission lines (DC‐GIL) filled with SF6 are thoroughly studied. The influences of volume and surface conductivity of the insulator on the surface charge and consequent electric field distribution are discussed. An improved method is introduced to obtain the distribution of surface charge with considerable accuracy and efficiency for the calculation. It is found that with increasing the volume conductivity, the dominative conduction mechanism changes from surface conduction to bulk conduction, while the inverse variation appears with increasing the surface conductivity. During the variation of electric conductivity, obvious effect of surface charge accumulation is found on the electric field distribution involving the variation of peak electric field strength and its location. Besides, high charge density usually appears along with low peak field strength during this variation. It can be concluded that the surface charge accumulation should be paid special attention when analysing the insulation characteristics of tri‐post insulators. The variation of volume and surface electric conductivity should be thoroughly considered. [ABSTRACT FROM AUTHOR]

High-voltage direct current (HVDC) links are starting to become widely implemented thanks to their interesting advantages such as reduced operation losses, the absence of reactive power, which allows energy transport via underground cables over long distances, and improved power control. The latter advantage is very essential for renewable energy resource integration into power grids. However, a thorough understanding of the behavior of insulation systems for HVDC components is critical so as to ensure a more reliable service. Indeed, the existence of the direct current (DC) voltage in HVDC components may induce surface and space charge accumulation that can stress insulation further or even promote discharge inception and propagation. As such, this work focuses on showcasing the effect of surface charge on streamers that develop on the interface of liquid–solid insulation due to the advent of lightning impulse (LI) voltage in the HVDC link. This study was performed using finite-element-based numerical simulations that include a quasi-electrostatic model for surface charge accumulation and an electrohydrodynamic fluid model for streamer initiation and propagation. The geometry used was point–plane configuration where the high voltage is applied to the needle electrode located above the liquid–solid interface. The obtained results suggest that streamer initiation is affected by both the accumulated surface charge density and polarity. For a positive streamer, an accumulation of positive surface charge increases the discharge inception voltage as a result of a weakening in the electric field, while an accumulation of negative surface charge decreases the discharge inception voltage due to an intensification in the electric field. Moreover, streamer travel distance and velocity are also both shown to be affected by surface charge accumulation. [ABSTRACT FROM AUTHOR]

In this article, the influence of polishing orientation on surface charge accumulation and flashover characteristics of the basin spacer in a downsized dc-gas insulated transmission line (GIL) are explored by experiments. Results show that the surface charge distribution of the polished spacers is different from the untreated one. Heteropolar charges can be observed in the polished area and outward expansion area under prestressing condition. The flashover voltages of all polished spacers are decreased. The radial polishing (RP) has the greatest impact on the flashover voltage, and the flashover voltage of the radially polished spacer is decreased by 11% under positive prestressing condition. The metal dust adsorptions of the spacers are also measured, which shows that the radially polished spacer is easier to absorb metal dust and the metal dust diffuses in the radial direction. SEM and energy spectrum scanning of different spacers show that there are more exposed alumina particles on the surface of the polished area. The microdischarge induced by alumina particles is the source of heteropolar charges. When the polished area of the spacers is repaired with epoxy paint, heteropolar charges disappear on the surface of the repaired spacer. It is confirmed that charge accumulation and flashover along the spacer surface are mainly affected by the change of surface morphology on the polished area. [ABSTRACT FROM AUTHOR]

In this article, the mechanisms of surface charging and surface modification of epoxy spacer affecting the lifting voltage and the motion trajectory of spherical metal particles in a downsized dc gas insulated transmission line (GIL) are investigated by simulations and experiments. Results show that the lifting voltage can be predicted with much accuracy by calculating the electric field distribution under the capacitive condition. Prestressing leads to a 27% decrease of lifting voltage, which is traceable to that surface charging making a major contribution to the enhancement of electric field force. Direct fluorination is proven as an effective modification method to improve the insulation performance of epoxy spacer again. The lifting inclination is significantly inhibited after treatment because of less surface charge accumulation and more rationalized electric field distribution. The trajectory simulation results indicate that more serious surface charging can activate more metal particles to lift up and drive them to more collisions. The lifting probability and velocity of metal particles around the epoxy spacer are markedly decreased by fluorination, which is a promising treatment for dc GIL/gas insulated switchgear (GIS) application. [ABSTRACT FROM AUTHOR]

In this study, a downsized direct current (dc)-gas-insulated transmission line (GIL) model is applied to investigate the surface charging and discharging characteristics of the basin-type spacer in 0.1-MPa SF6 and air. Under a low electric field, the surface charge accumulation is dominated by the bulk conduction of the spacer. As the charging voltage increases, gas ionization occurs in the localized strong electric field, taking over the dominant position. In 0.1-MPa SF6 gas, flashovers typically develop along the convex surface of the spacer under both positive and negative voltages because the homo-charge accumulation induced by brush discharges on the concave surface aggravates the electric field distortion at the convex side. In air, the dc flashovers have the polarity effect. Under the negative voltage, the flashover development is similar to that in SF6 gas. But for positive polarity, the space charge region of positive polarity intensifies the electric field ahead of the corona region, thus promoting the air-gap breakdown at the concave side of the spacer. [ABSTRACT FROM AUTHOR]

This paper presents a one-step method for fabricating a PDMS optical lens based on the surface charging and edge pining effects of a PDMS droplet. This method works by electrically lifting the air-liquid PDMS interface initially stabilized by the edge pining effect of a PDMS droplet on a polymethyl methacrylate (PMMA) substrate. The electrical lifting was achieved under the force interaction between the negative surface charges of the PDMS droplet and the non-uniform electric field generated by a needle-plate electrode pair. Experimental results show that the electrical lifting was achieved in about 10 seconds. With the increase of the applied electric field, the magnification of the fabricated lens increases. Fabricating a lens with a resolution of 32 lp/mm and a magnification of 23.92 times was obtained under an averaged electric field of 12500 V/cm. Chlorophyll-fluorescence-based living algae detection with the PDMS lens and a smartphone imaging system was successfully achieved. [Display omitted] [ABSTRACT FROM AUTHOR]

The dynamics of ionization waves (IWs) in atmospheric pressure discharges is fundamentally determined by the electric polarity (positive or negative) at which they are generated and by the presence of memory effects, i.e. leftover charges and reactive species that influence subsequent IWs. This work examines and compares positive and negative IWs in pulsed plasma jets (1 μ s on-time), showing the difference in their nature and the different resulting interaction with a dielectric BSO target. For the first time, it is shown that a surface charging memory effect is produced, i.e. that a significant amount of surface charges and electric field remain in the target in between discharge pulses (200 μ s off-time). This memory effect directly impacts IW dynamics and is especially important when using negative electric polarity. The results suggest that the remainder of surface charges is due to the lack of charged particles in the plasma near the target, which avoids a full neutralization of the target. This demonstration and the quantification of the memory effect are possible for the first time by using an unique approach, assessing the electric field inside a dielectric material through the combination of an advanced experimental technique called Mueller polarimetry and state-of-the-art numerical simulations. [ABSTRACT FROM AUTHOR]

The interpretation of the surface charge pattern of spacers in gas-insulated transmission lines (GIL) is a research topic with great importance, which requires a comprehensive understanding of charge behaviors at physical interfaces. Here, we report a surface charging phenomenon of spacers in the presence of metal particles inside the direct current (DC) GIL. The charging of spherical metal particles on the spacer surface appears as dotted discontinuously distributed charge spots, which are due to the charge injection from the induced charge of the metal particle and gas ionization over the metal particle surface. Concentrically distributed bipolar charge patterns are seen to build up, which are due to the surface trapping of charges from gas ionization at the end tip of the acicular metal particle. The lateral type of ionization obeys the law of dielectric barrier discharge of the needle-plate electrode in an intense DC electric field, which may bring significant influence on the safety of the spacer. The study in this letter provides direct evidence demonstrating the surface charge patterns of spacers in the presence of metal particles, which serves as an important basis for the design of DC GIL. [ABSTRACT FROM AUTHOR]

Free metal particle can affect surface charge accumulation on epoxy insulator installed in gas-insulated transmission line (GIL) or gas-insulated switchgear (GIS), which results in reduction of surface flashover voltage thus threatening the safe operation of the power equipment. This article reports on the charge accumulation behavior on a real size epoxy insulator with bouncing metal particle under DC voltage. A coaxial electrode system was designed for the test under −30 kV, a metal particle-launching system was employed to inject the bouncing linear particle to the insulator surface. The charge distribution was measured by a Kelvin-type probe, and the influence of the particle on the charge accumulation was analyzed with the help of electric field simulation. The results showed that there were mainly two moving patterns of the bouncing particle: the charges were accumulated with speckle shape and the charged particle that hit the edge of electrode had more remarkable influence on the charge accumulation than other particles. It is suggested that the charge distribution feature is dependent upon the collision point and the trajectory of the bouncing particle. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulation has been employed to study conformational rearrangements induced by an external field in uniformly charged polypeptides adsorbed on the surface of an oppositely charged gold nanoparticle, whose polarization direction varies with a frequency corresponding to the microwave electric field. The averaged angular and radial distributions of atom densities have been calculated for the polyelectrolytes adsorbed on the nanoparticle surface. The simulation has shown the formation of a ring-shaped fringe of polyelectrolyte units encircling the gold nanoparticle in its equatorial region. The density of the fringe of an adsorbed polyelectrolyte macromolecule on the nanoparticle surface depends on both the total charge of the nanoparticle and the fraction of charged units in the macromolecule. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy insulator installed in gas-insulated transmission line (GIL) and gas-insulated switchgear (GIS) has been recognized as a crucial factor for electric field distortion that results in the reduction of surface flashover voltage. This article reports on the gaseous ionization dependence of the charge accumulation pattern on a real-size epoxy insulator with multiarc surface profile by using various gas atmospheres. A coaxial electrode system was designed to investigate the charging behavior under dc voltages of −10, −20, and −30 kV. The insulator and electrodes were placed in a metal-enclosed test chamber, which was filled with 0.1 MPa air or 0.4 MPa SF6/N2 mixture to estimate the influence of the gas atmosphere on the charge accumulation behavior by a Kelvin-type probe. The accumulation mechanism and the electric field distortion induced by the charges were demonstrated based on numerical simulation. The results indicated that positive charges were accumulated in the shape of speckle on insulator surface in air, whereas both positive and negative charges were accumulated in SF6/N2 mixture and positive charge speckles appeared in SF6/N2 mixture only when the voltage raised up to −30 kV. It is considered that the charge accumulation behavior is determined by the competition result among the bulk, the gas and the surface conductions. As compared with the case in air, gaseous ionization in SF6/N2 mixture is more difficult to occur, which leads to the obvious difference in the charge accumulation pattern. [ABSTRACT FROM AUTHOR]

Charges due to ionization at conductors at low electric field serves as the main source of charge carriers that is responsible for surface charge enhancement, especially for hetero-polar charges on the convex surface side of spacers inside DC gas-insulated transmission lines (GILs). In this paper, simulation results of charge generation processes from gas side, including natural ionization, micro-discharge and field emission, are presented. The results show that for the case where the electric field strength is -6.548 kV/mm and the gas pressure is 0.4 Mpa, when conductor roughness Ra is lower than 24.16 µm, natural radiation ionization is the main cause of the dark current. When Ra is between 24.16 µm and 188.59 µm, the dark current is dominated by micro-discharge. The Fowler-Nordheim (F-N) field emission occurs when Ra exceeds 188.59 µm. Considering the roughness of the conductor in the actual GIL, the increase in the dark current due to local roughness is mainly due to micro-discharge rather than F-N field emission. The results in this paper provide an important part for further determining of conductor surface conditions in high voltage direct current (HVDC) GILs and serve as an important reference for completion of the surface charging model of spacers under DC. [ABSTRACT FROM AUTHOR]

In this paper, the transient process of negative DC corona generated with needle to plane electrode covered by polymer film is investigated by numerical simulation considering air plasma chemistry. The variation in plasma species in corona discharge and the transient process of charge accumulation on the film are examined. Moreover, the electric field and the mean electron energy distribution on the sample surface are discussed. Obtained results indicate that during the corona process, O 2 +, O 4 + and N 4 + are the dominant positive ions, O 2 − and O are the main negative ion and the neutral particle, respectively. The charge accumulation region expands along the radial direction and the charge density increases gradually. In addition, the discharge channel shape is changed from column to cone with time, which is attributed to the electric field modification achieved by the accumulated charges. In 2000 ns, the mean electron energy distribution on the polymer surface varies between 2.1 and 5.8 eV and finally stabilizes to 3.7 eV, thus the electrons can overcome the barrier at gas-solid interface and become injected into the polymer bulk. It is suggested that the polymer surface charging transient is highly associated with the plasma behavior. [ABSTRACT FROM AUTHOR]

This article adds to the other recent ones that have been published, mainly in this magazine that is, in our view, becoming a forum for discussion of this which is the electric field on the surface of a charged spherical conductor. We recently published an article that discussed three models for finding the recalcitrant factor 1/2 that chase many fans of this electrostatic issue. In this way, this text was elaborated, exclusively, to try to clarify and oppose, some interpretations put in a later recent article [1] that defends a proper integral to find the stubborn factor. In this way, we reaffirm the method of superposition of the ring field to discuss the field's behavior through a uniformly charged spherical surface, trying to reach a consensus. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy insulator installed in gas insulated switchgear (GIS) or gas insulated transmission line (GIL) has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on surface charge accumulation behavior on a actual epoxy insulator for 100 kV GIL prototype with multi-arc surface profile. A coaxial electrode system is used to investigate the charging behavior under DC voltages with metal particles positioned at various positions of the surface so as to estimate its influence on the charge accumulation behavior using a Kelvin type probe. The results show that positive charges are accumulated mainly on the nonplanar region around the high voltage electrode in the shape of speckles, and the average charge distribution along the radial direction presented a double-peak feature. Moreover, the charge accumulation is enhanced by metal particles contacting to the grounded electrode. Using a numerical simulation method, it is suggested that the charge accumulation is mainly determined by gaseous ionization which is enhanced by the metal particle induced electric field distortion. [ABSTRACT FROM AUTHOR]

The accumulation of surface charges is a crucial challenge, especially for HVDC components. Accumulated surface charges can change the electric field distribution and generate weak points, especially in case of superimposed transient voltages and, therefore lower the performance e.g. of insulators. Hence, an accurate measurement of the surface potential and so the surface charges is necessary to optimize these components. Commonly, the surface potential is measured with an electrostatic voltmeter. In this study a procedure for determining the spatial impulse response of a compensating electrostatic voltmeter depending on only the surface to probe distance is presented. Based on the performed measurements a mathematical model is developed to describe the capacitive influence and significance of the local surface potential on the measurement result. The actual measurement value is a weighted and averaged value given by the actual position and its surrounding, which is also confirmed by numerical simulations. The performed procedure enables high accuracy of the measurement of surface potentials and so of surface charges using different types of electrostatic voltmeters and shows the limitation of the measurement procedure. This knowledge increases the possibility to design optimized components for HVDC systems. [ABSTRACT FROM AUTHOR]

This paper presents a 3-D, fully kinetic particle-in-cell (PIC) simulation study of plasma charging for small, irregularly shaped, composite asteroids in the solar wind. Three types of asteroid internal structures are considered: 1) a homogeneous composition of regolith; 2) a single hard rock; and 3) a composite of hard rock core covered with a regolith outer layer. The simulation model resolves the plasma flow field, asteroid surface differential charging, and asteroid internal electric field self-consistently. The results show that while the ambient plasma condition and surface property determine surface charging, the internal composition substantially affects the subsurface electric field inside an asteroid. [ABSTRACT FROM AUTHOR]

The dynamic behavior of surface charging on spacers in DC-GILs can be influenced by multi-factors including the non-uniform distributed electric field as well as the time-varying temperature gradient. In this paper, the time-varying effect of surface charging phenomenon on spacers is studied and a time-varying mathematical model is established, based on the influence of temperature and electric field on the ion mobility at the gas phase and the bulk conductivity in the solid phase. The results verify that the bulk conductivity can be greatly influenced by temperature, which leads to an increase in the surface charge density on the spacer. This allows the surface charge accumulation to stabilize more quickly. However, the ion mobility from the gas phase is less affected by temperature. When the non-uniform distributed electric field changes from 1.3 to 6.4 kV/mm, ion mobility is less influenced and the surface charge density on the spacer varies slightly. In this case, the effects of the non-uniformly distributed electric field in surface charge density variation is much smaller and can be ignored. [ABSTRACT FROM AUTHOR]

[Display omitted] • An ultraviolet irradiation in vacuum technique enhancing flashover voltage of SIR. • Illustrate the influence of UVIV on the chain structure of SIR. • Establish a relation between crosslinking of SIR and surface trap parameters. • Explain the effects of surface traps on surface charging and flashover. • Clarify the UVIV improved flashover mechanisms from microscopic to macroscopic. In surface science, surface flashover, which poses a severe danger to the safe operation of modern silicone rubber (SIR)-based electrical equipment, is a continuous discharge event that happens when an intense electric field is produced along the gas-solid interface. To improve the flashover performance, the ultraviolet irradiation in vacuum (UVIV) technique is proposed to modify the SIR surface and the DC flashover threshold increases approximately 14.8 % after 6 h UVIV treatment. Then, the influence mechanisms of UVIV are investigated from microscopic molecule modification to macroscopic flashover performance: The UVIV generates high-energy photons to break C H and Si C bonds in SIR chains, and atoms, group, side chains, and free radicals in chains recombine through the thermally dynamic, causing SIR chains to crosslink. The crosslink chain structure enhances the deep trap energy around the Si O Si bond and introduces large amounts of deep traps. The increment in surface deep trap energy and density captures electrons. It establishes a high electrostatic near the cathode barrier that impedes subsequent electron injection, causing surface charge density decreases far away from the cathode. The reduced surface charges restrict the collision ionization in gas, finally increasing the DC surface flashover voltage through UVIV treatment. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on polymer insulating material has been recognized as an important factor for electric field distortion that results in reduction of surface flashover voltage. This paper reports on the charge accumulation behavior between a pair of finger-shaped electrodes on epoxy/Al2O3 nanocomposites under dc voltage superimposed by repetitive pulses. The charge distribution was measured by means of an electrostatic voltmeter, from which the average charge density could be calculated. Effects of dc voltage, nanofiller content, and pulse voltage on charge accumulation behavior were investigated. Obtained results showed that with the increase in the filler content from 0 wt% to 5 wt%, the average charge density increased initially then appeared to decrease. The superposition of repetitive pulses on dc voltage led to a remarkable growth in charge accumulation as compared with that when only dc voltage was applied. It is suggested that the charges are originated from local gaseous ionization and/or electrode injection, which is determined by the combined voltage. The charge density is dependent upon the surface trap, which is affected by nanofiller content. The superposition of repetitive pulse is considered as a possible reason to encourage local gaseous ionization that results in enhanced accumulation of surface charge. [ABSTRACT FROM AUTHOR]

Surface charge accumulation on epoxy based nanocomposites under DC stress with and without the presence of a magnetic field was investigated in this work. Two mm-thick sheet samples were prepared by adding 60 nm-Al 2 O 3 particles into epoxy with filler content of 1 to 5 wt%. A pair of finger-shaped electrodes was employed to introduce electric charges onto the sample surface under DC stress of ±5 and ±10 kV. The magnetic field was established by using a pair of permanent magnets, by which a magnetic flux density of 100 and 180 mT was achieved. Surface charge between the electrodes was measured by means of a Kelvin type electrostatic voltmeter, and the influence of nano-filler content and magnetic flux density on charge distribution as well as charge density was estimated. The results indicate that increasing nano-filler content from 0 to 5 wt%, the average charge density increased initially then decreased. The presence of a magnetic field results in a deflection of charge profile as compared with that formed without a magnetic field. The charge density increased as the magnetic flux density increased from 0 to 180 mT. It is suggested that the charge trajectory close to high voltage electrode varies by the combined electric-magnetic force, by which electric field recovery in such a region is facilitated thus more charges are encouraged to accumulate on the surface. [ABSTRACT FROM AUTHOR]

Surface charge accumulation of polymer insulating materials is harmful to the safe operation of electrical equipment, especially under DC electric field excitation. In order to ensure the safety and stable operation of HVDC power system such as Gas-insulated transmission line, it is necessary to understand the influence of the surface charge on the flashover and improve the surface charge dynamic characteristics. In this paper, Epoxy resin (EP) is deposited by SiOx thin films with different plasma treatment conditions. The flashover voltages are measured with and without surface charges. The results show that the flashover occurs at lower voltage due to the accumulated charges on the EP surface. In particular, the surface charge with the same polarity of flashover discharge can reduce the surface flashover voltage significantly. Moreover, the charge decay rate is increased up to 90% by plasma treatment of 3 min, corresponding flashover voltage is increased. In addition, the flashover voltages of samples during the surface charge dissipation are obtained. Both static impact index I and dynamic impact index S are introduced to estimate effect of surface charge on dielectric surface flashover. [ABSTRACT FROM AUTHOR]

A spacer is a challenging part of high voltage direct current (HVDC) gas-insulated substations and gas-insulated transmission lines. This paper proposes a novel design of HVDC spacers by self-adaptively controlling the surface charge. The paper briefly reviews dielectric modification methods that aim to limit surface charge accumulation. A novel design of HVDC spacer is introduced that is based on the concept of adaptively controlling surface charges using nonlinear materials, and its surface charge control and regulation abilities are investigated. The surface charge accumulation and decay properties of the novel spacer are compared to a downsized spacer. The results show that the proposed model spacer can restrict surface charge accumulation in the charge adaptive control region of the spacer. Doping the nonlinear material can facilitate surface charge decay in the charge adaptive control region when the electric field exceeds a threshold. These positive results represent a new idea of designing a suitable spacer to avoid surface flashover in HVDC SF6 apparatus. [ABSTRACT FROM AUTHOR]

The surface charges that accumulate on polypropylene (PP) film can induce electrical field distortion and surface flashover, which accelerate the electrical aging of a capacitor. This paper investigated the effect of combined voltage on the surface charge behaviors and flashover voltage and a modification method to inhibit the accumulation of surface charge. The carrier mobility in different conditions was calculated using a surface potential decay process to analyze the transportation of surface charges. Samples that were fluorinated for 15, 30, 45 and 60 min and unfluorinated samples were prepared prior to experiments. The samples were corona charged with a pair of needle-plate electrodes by DC voltage and a combination of DC voltage and pulse voltage. The flashover experiments were performed under DC voltage, pulse voltage and superimposed voltage in atmospheric air. The results indicate that the maximum carrier mobility and maximum flashover voltage can be obtained when the samples are surface modified for 45 min. The surface charge density decreases with an increase in the carrier mobility under DC voltage. Under a combination of DC voltage and pulse voltage, the initial surface charge density is influenced by both the carrier mobility and the pulse voltage. The results suggest that surface modification for a certain time can significantly inhibit the surface charge accumulation, improve the carrier mobility and increase the flashover voltage. [ABSTRACT FROM AUTHOR]

The space charge on the surface of solid dielectric has great influence on the surface dielectric barrier discharge (SDBD). In this paper, the surface space charge of SDBD is effectively regulated by the effect of electrically pre-stressing of high DC electric field to improve the dynamic performance of ion wind thruster. The conduction current, surface charges, thrust and thrust-to-power ratio are measured respectively for the ion wind thruster with and without the effect of electrically pre-stressing. The experimental results show that compared with the ion wind thruster without the effect of electrically pre-stressing, the instantaneous polarization current of the SDBD ion wind thruster with the effect of electrically pre-stressing is reduced by 42.7%, and the attenuation constant of the relaxation polarization current is reduced by about 28.8%, which effectively reduces the relaxation polarization loss of the thruster under the alternating electric field. In addition, the discharge time of anode and cathode increases respectively by about 20.0% and 43.3%, and the variation of surface space charge increases by about 50.6% in one voltage cycle. The saturation thrust of the thruster is increased from 1070 μN/m to 1660 μN/m by about 55.1%. The maximum thrust-to-power ratio of the thruster is increased from 993 μN/kW to 2125 μN/kW by about 114.0%. • Initial instantaneous value of the response current of the PVDF under the pre-electric stress is reduced by about 42.7%, and the attenuation constant of the relaxation polarization current is reduced by about 28.8%, compared with the PVDF without the pre-electric stress. • Comparing with the SDBD thruster without the pre-electric stress, the anode discharge time increases by about 20.0%, the cathode discharge time increases by 43.3%, and the surface space charge variation increases by about 50.6% during the discharge process. • The saturation voltage of the SDBD ion-wind thruster increased from 4.8 kV to about 5.6 kV, and the saturation thrust increased from 1070 μN/m to about 1660 μN/m, with the increased amplitude of 16.7% and 55.1%, respectively. • Due to the regulation effect of negative space charge on charged particles, the current passing through the SDBD thruster is relatively small. The thrust-power ratio increased by about 114.0%. [ABSTRACT FROM AUTHOR]

Polyimide (PI) films have excellent electrical, mechanical and thermal properties in aspect of resisting corona, aging and radiation. However, the pulse voltage combined with dc voltage often causes concentration of local electrical field, which makes the surface charge behaviors more complex and threatens the system. As a means of surface treatment, direct fluorination has been proved as an effective way to improve the polymer properties, without compositing the bulk characteristics. Therefore, this paper intends to reveal the effects of fluorination on surface charge coupling behaviors of the PI films under dc and pulse voltage combination. The PI samples fluorinated for 0, 15, 45 and 60 min were obtained. Surface corona discharging was stressed under the combination of dc and pulse voltage. The surface charge accumulation, decay and distribution were measured coupled with an analysis of trap distribution. The results show the surface charge dynamic behaviors are strongly correlated with the fluorination time, pulse voltage amplitude and polarities of the dc and pulse voltage combination. The trap distribution results imply that the effect of fluorination and charging condition attribute to the change of trap depth and amount. Besides, surface charge behaviors are greatly improved by appropriate fluorination. [ABSTRACT FROM AUTHOR]

In this study, a comprehensive analysis of the pH-dependent contact angles, freezing temperatures and ice adhesion on aluminium samples is presented. It is not yet known whether externally applied electric fields or charged interfaces sufficiently affect the heterogeneous freezing and ice adhesion in order to provide technical solutions for refrigeration engineering, de-icing techniques and food preservation. It was found that surfaces charges that are generated on polished aluminium samples by changing the pH value of the adjacent KCl solution significantly reduce the advancing contact angle. The effect of surface charges on the freezing behaviour was determined by cooling an array of droplets of KCl solutions with pH values between 3 and 12 with a cooling rate of 1 K min−1. Ice adhesion was evaluated using an in-house developed pusher test at -10 °C in a climate chamber. Both icephobicity tests revealed that surface charges seem ineffective to significantly change the freezing behaviour and ice adhesion strength on polished aluminium samples. [Display omitted] • The advancing contact angles reach their maximum at the potential of zero charge. • Higher ion contents increase the achievable supercooling and decreases ice adhesion. • There is no significant effect of pH-generated surface charge on icephobicity. • Heterogeneous freezing follows a generalised extreme probability density function. • Naturally occurring charges are insufficient to provide icephobicity on Al samples. [ABSTRACT FROM AUTHOR]

In the bridged vacuum gaps, the secondary electron emission avalanche (SEEA) occurring along the surface of solid insulator and the resultant surface charging play a crucial role in the progress of surface discharge. In order to sophisticate the insulation design of high voltage vacuum devices, analysis and control of SEEA charging are of importance. Boersh et al. have proposed a boundary condition on the surface of an insulator to solve the charge distribution at an equilibrium state of SEEA charging. The boundary condition can be easily adopted for analyzing two dimensional SEEA charge distributions. However, the above condition by Boersh et al. cannot be applied in the case of three dimensional distributions. In this paper, the authors newly developed the boundary condition for three dimensional applications and created a numerical simulation code for analyzing three dimensional SEEA charge distributions. Two types of insulator were examined in this study; one was a solid cylinder and the other a hollow cylinder. In the case of the solid cylinder, electric field strength on the cathode was calculated and compared with the measurement. On the other hand, in the case of the hollow cylinder, the calculated result was compared with the charge distribution experimentally obtained by a movable electrostatic probe system. These calculation and measurement results have shown reasonable agreement and we have validated the newly developed numerical simulation method for three dimensional SEEA charge distributions. [ABSTRACT FROM AUTHOR]

The development of electric fields in gas-solid insulation systems under dc voltage stress goes hand in hand with the accumulation and decay of charges on dielectric interfaces. The charge transport through the solid insulator and the gas is determined by the electric properties of the involved insulating materials. Therefore, the nonlinearly field-dependent volume conductivity of a gas, resulting from a constant charge generation rate by natural ionization has to be considered. The transient field distribution on insulators under dc voltage is investigated theoretically, using a gas model, which takes into account the physical characteristics of insulating gases like air and SF6 as well as the effects resulting from electron emission from the electrodes. The influence of the ion pair generation rate in the gas, the electric field strength, and the volume and surface conductivity of the solid insulating material on the development of the electric field is investigated on cylindrical and conical insulators which are typical for gas insulated systems. Results of calculations using the gas model are compared to simulations assuming constant gas conductivity. The simulation results are verified by measurements of the surface potential on cylindrical epoxy resin insulators in air. [ABSTRACT FROM AUTHOR]