Showing papers on "Insulator (electricity) published in 2018"
TL;DR: In this paper, the authors used scanning probe microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy to show that TDS Na3Bi is 2D topological insulators with bulk bandgaps >400 meV in the absence of electric field.
Abstract: The electric field induced quantum phase transition from topological to conventional insulator has been proposed as the basis of a topological field effect transistor [1-4]. In this scheme an electric field can switch 'on' the ballistic flow of charge and spin along dissipationless edges of the two-dimensional (2D) quantum spin Hall insulator [5-9], and when 'off' is a conventional insulator with no conductive channels. Such as topological transistor is promising for low-energy logic circuits [4], which would necessitate electric field-switched materials with conventional and topological bandgaps much greater than room temperature, significantly greater than proposed to date [6-8]. Topological Dirac semimetals(TDS) are promising systems in which to look for topological field-effect switching, as they lie at the boundary between conventional and topological phases [3,10-16]. Here we use scanning probe microscopy/spectroscopy (STM/STS) and angle-resolved photoelectron spectroscopy (ARPES) to show that mono- and bilayer films of TDS Na3Bi [3,17] are 2D topological insulators with bulk bandgaps >400 meV in the absence of electric field. Upon application of electric field by doping with potassium or by close approach of the STM tip, the bandgap can be completely closed then re-opened with conventional gap greater than 100 meV. The large bandgaps in both the conventional and quantum spin Hall phases, much greater than the thermal energy kT = 25 meV at room temperature, suggest that ultrathin Na3Bi is suitable for room temperature topological transistor operation.
89 citations
TL;DR: In this article, the authors discuss how to push four-wave mixing performance in integrated nonlinear platforms such as AlGaAs-on-insulator waveguide and micro-resonators.
Abstract: We discuss how to push four-wave mixing performance in integrated nonlinear platforms. Recent optical signal processing demonstrations in AlGaAs-on-insulator waveguide and microresonators are reviewed.
72 citations
TL;DR: In this article, the spin-orbit torque generated from the Pt oxide can be controlled electrically through voltage-driven oxygen migration, which enables electrical switching of perpendicular magnetization in a ferrimagnet sandwiched by insulating oxides.
Abstract: Current-induced magnetization switching through spin-orbit torques is the fundamental building block of spin-orbitronics, which promises high-performance, low-power memory and logic devices. The spin-orbit torques generally arise from spin-orbit coupling of heavy metals. However, even in a heterostructure where a metallic magnet is sandwiched by two different insulators, a nonzero spin-orbit torque is expected because of the broken inversion symmetry; an electrical insulator can be a source of the spin-orbit torques. We demonstrate current-induced magnetization switching using an insulator. We show that oxygen incorporation into the most widely used spintronic material, Pt, turns the heavy metal into an electrically insulating generator of the spin-orbit torques, which enables the electrical switching of perpendicular magnetization in a ferrimagnet sandwiched by insulating oxides. We also show that the spin-orbit torques generated from the Pt oxide can be controlled electrically through voltage-driven oxygen migration. These findings open a route toward energy-efficient, voltage-programmable spin-orbit devices based on insulating metal oxides.
68 citations
TL;DR: In this paper, a corona discharging system was employed to charge the epoxy samples before the charge dissipation measured, and the surface flashover voltages of samples with different modification time under DC voltage were also measured, the results are obtained from the research.
Abstract: Epoxy disc-type spacer, as the major insulator of gas insulated transmission line, plays a significant role in the reliability and safety of the entire power grid. While surface charge accumulation on the spacer could induce flashover and accelerate degradation of the insulator, which threats the operation of high-voltage DC transmission and grid. In this study, a corona discharging system was employed to charge the epoxy samples before the charge dissipation measured, and the surface flashover voltages of samples with different modification time under DC voltage were also measured, the results are obtained from the research. It is found that the carrier mobility and surface flashover voltage of samples are affected by modification time, and maximum value of both can be obtained when the sample is modified for 60 min. Under the combined voltages, the initial surface charge density and carrier mobility are affected by both pulse voltage and modification time. It is indicated that surface modification is an appropriate method which can significantly inhibit the surface charge accumulation, and improve the flashover characteristics of epoxy sample by increasing carrier mobility. The trap distribution characteristics suggested that the modification treatment and charging condition have a significant effect on the depth and density of trap.
51 citations
TL;DR: In this paper, the surface charge distribution on the fullerene-filled epoxy resin insulators with different filler loadings is obtained by using the Kelvin-probe method and an advanced inversion algorithm.
Abstract: Surface charge accumulation on the insulator surface and the resulting flashover voltage reduction are considered the primary factors to hinder the large-scale use of HVDC system, especially the gas-insulated system. In this study, Buckminster-fullerene C60 of different loadings is introduced into epoxy resin for the purpose of restricting the mobility of charge carriers within the material and thus suppressing the charge accumulation on the insulator surface under dc voltage. Experimental results have shown that with the addition of tiny amount of fullerene C60 into epoxy, the conductivity of the composites decreases significantly with the loading and reaches its minimum around 100∼200 ppm, which can be as low as 20% that of neat epoxy. By using the Kelvin-probe method and an advanced inversion algorithm, the surface charge distribution on the fullerene-filled epoxy resin insulators with different filler loadings are obtained. It is observed that the addition of 200 ppm fullerene C60 into epoxy resin can effectively suppress the charge accumulation on the insulator surface. The interfacial polarization model is adopted to interpret the mechanism of surface charge accumulation, which shows that reducing the bulk conductivity of the insulator can effectively suppress the surface charging. This paper provides a potential solution for engineering epoxy based insulators used for the dc power system.
46 citations
TL;DR: In this paper, the Ohmic contact dilemma is resolved by formulating an equivalent circuit appropriate for assessing the properties of an insulator and then recognizing that an Ohmic-contact is obtained when the injection limited current density from the cathode electrode is greater than that of the operative bulk-limited current density.
Abstract: The current density–electric field ${(}{J}-\xi {)}$ characteristics of four insulators of dramatically different electrical qualities are assessed in terms of their operative electronic conduction mechanisms. Conduction in the two high-quality insulators is dominated by Ohmic conduction and Fowler–Nordheim tunneling, whereas conduction in the two low-quality insulators involves Ohmic conduction and space-charge limited current (SCLC). Ohmic conduction and SCLC are somewhat puzzling mechanisms for contributing to insulator leakage current since they require the existence of an Ohmic contact at the cathode. Our conventional understanding of an Ohmic contact makes it difficult to ascertain how an Ohmic contact could be formed to a wide bandgap insulator. This Ohmic contact dilemma is resolved by formulating an equivalent circuit appropriate for assessing the ${J}-\xi $ characteristics of an insulator and then recognizing that an insulator Ohmic contact is obtained when the injection-limited current density from the cathode electrode is greater than that of the operative bulk-limited current density, i.e., Ohmic or SCLC for the four insulators under consideration.
42 citations
TL;DR: The results show how the nonlinearities and the resistive transition originate from a massive creation of hot electrons under an electric field and give new insights for the control of the long-lived states reached under anElectric field in these systems which has recently open the way to new functionalities used in neuromorphic applications.
Abstract: Out of equilibrium phenomena are a major issue of modern physics. In particular, correlated materials such as Mott insulators experience fascinating long-lived exotic states under a strong electric field. Yet, the origin of their destabilization by the electric field is not elucidated. Here we present a comprehensive study of the electrical response of canonical Mott insulators GaM_{4}Q_{8} (M=V, Nb, Ta, Mo; Q=S, Se) in the context of a microscopic theory of electrical breakdown where in-gap states allow for a description in terms of a two-temperature model. Our results show how the nonlinearities and the resistive transition originate from a massive creation of hot electrons under an electric field. These results give new insights for the control of the long-lived states reached under an electric field in these systems which has recently open the way to new functionalities used in neuromorphic applications.
38 citations
TL;DR: In this paper, different types of insulators, namely, aluminum oxide (Al2O3), silicon nitride, and silicon oxide (SiO x ), were used as passivation layers in CIGS thin-film solar cells.
Abstract: In this work, metal–insulator–semiconductor structures were fabricated in order to study different types of insulators, namely, aluminum oxide (Al2O3), silicon nitride, and silicon oxide (SiO x ) to be used as passivation layers in Cu(In,Ga)Se2 (CIGS) thin-film solar cells. The investigated stacks consisted of SLG/Mo/CIGS/insulator/Al. Raman scattering and photoluminescence measurements were done to verify the insulator deposition influence on the CIGS surface. In order to study the electrical properties of the CIGS–insulator interface, capacitance versus conductance and voltage ( C–G–V ) measurements were done to estimate the number and polarity of fixed insulator charges ( Qf ). The density of interface defects ( D it) was estimated from capacitance versus conductance and frequency ( C–G–f ) measurements. This study evidences that the deposition of the insulators at high temperatures (300 °C) and the use of a sputtering technique cause surface modification on the CIGS surface. We found that, by varying the SiO x deposition parameters, it is possible to have opposite charges inside the insulator, which would allow its use in different device architectures. The material with lower D it values was Al2O3 when deposited by sputtering.
36 citations
TL;DR: In this paper, a comparative analysis of TCO modulators was conducted by reviewing several representative designs based on the uniform concentration accumulated carrier model and the classical continuous carrier distribution model, and applied the quantum moment model to analyze the free carrier distribution of the TCO based metal-oxide-semiconductor (MOS) capacitor for the first time, and reveal significantly different device physics compared with previous simulation models.
Abstract: Electron accumulation in transparent conductive oxides (TCOs), when driven by a gate voltage, is capable of inducing extremely strong electro-optic absorption at the telecommunication wavelength window due to the epsilon-near-zero (ENZ) effect and various waveguide modulators have been proposed in recent years. This paper conducts a comparative analysis of TCO modulators by reviewing several representative designs based on the uniform concentration accumulated carrier model and the classical continuous carrier distribution model. We also apply the quantum moment model to analyze the free carrier distribution of the TCO based metal-oxide-semiconductor (MOS) capacitor for the first time, and reveal significantly different device physics compared with previous simulation models. The quantum moment model predicts a much higher driving voltage in order to turn the TCO materials into ENZ and a stronger modulation strength compared with the classical model. Especially, the requirement of the higher gate voltage brings a great challenge to the insulator layer as the electric field in the insulator is exceeding the breakdown strength, which raises the concern of reliability. In order to evaluate the accuracy of different models, we compare the simulation results with two of the most recent experimental papers and show that the quantum model has a better match in terms of the electro-absorption rate and the differential driving voltage. However, the quantum moment model still cannot explain some other experimental results, which may be induced by different modulation mechanisms.
34 citations
32 citations
TL;DR: In this paper, a field plate structure was employed to maximize the breakdown voltage by suppressing the electric field at the anode edge of Ga2O3-based vertical Schottky barrier diodes.
Abstract: Gallium oxide (Ga2O3) based vertical Schottky barrier diodes (SBDs) were designed for high voltage switching applications. Since p-type Ga2O3 epitaxy growth or p-type ion implantation technique has not been developed yet, a field plate structure was employed in this study to maximize the breakdown voltage by suppressing the electric field at the anode edge. TCAD simulation was used for the physical analysis of Ga2O3 SBDs from which it was found that careful attention must be paid to the insulator under the field plate. Due to the extremely high breakdown field property of Ga2O3, an insulator with both high permittivity and high breakdown field must be used for the field plate formation.
TL;DR: It was demonstrated that decreasing the number of columns in the post array allows for the dielectrophoretic trapping of nanometer-scale particles at voltages well below those reported in previous similar iDEP systems, illustrating how the iDEP channel configuration can be customized for specific applications.
Abstract: Insulator-based dielectrophoresis (iDEP) is a microfluidic technique used for particle analysis in a wide array of applications. Significant efforts are dedicated to improve iDEP systems by reducing voltage requirements. This study assesses how the performance of an iDEP system, in terms of particle trapping, depends on the number of insulating obstacles longitudinally present in the microchannel. In analogy with Kirchhoff’s loop rule, iDEP systems were analyzed as a series combination of electrical resistances, where the equivalent resistance of the post array is composed by a number of individual resistors (columns of insulating posts). It was predicted by the COMSOL model, and later confirmed by experimental results, that reducing the number of columns of insulating posts significantly affects the electric field distribution, decreasing the required voltage to dielectrophoretically trap particles within the post array. As an application, it was demonstrated that decreasing the number of columns in the ...
11 Jun 2018
TL;DR: In this article, the authors used electrostatic 2D simulations in the AC/DC module to predict the behavior of polluted insulators under AC voltage and applied different conductivity values.
Abstract: The knowledge of the distribution of the electric field within and around high voltage equipment is a crucial aspect of the design, exploitation and performance of high voltage insulators. It could be useful for the detection of defects in insulators. The objective of this study is predicting the behavior of polluted insulator under AC voltage. For thus, the distribution of the potential and the electric field along high voltage insulator is investigated using a numerical method. The commercial Comsol Multiphysics proved to be one of the best software used in 2D modeling. The potential and the electric field distributions along this insulator are simulated under various conditions: the two cases: clean and polluted insulators and applying different conductivity values. We used electrostatic 2D simulations in the AC/DC module. The results are auspicious and promising.
TL;DR: In this article, both field contamination experiments of HVDC (High Voltage Direct Current) transmission lines and wind tunnel contamination simulation tests were conducted, and pollution non-uniformity coefficient KT/B, KW/L and KH/M were proposed and obtained.
Abstract: In recent years, the air particulate pollutants formed by the combustion of fossil fuels and the emission of industrial waste gases have constantly been produced, and the polluted particles deposit also seriously affects social production and people’s lives. For instance, pollution-induced flashover is seriously threatening the safe operation of the power system, while insulator pollution non-uniformity has great influence on the flashover voltage of insulators. Therefore, in this paper both field contamination experiments of HVDC (High Voltage Direct Current) transmission lines and wind tunnel contamination simulation tests were conducted, and pollution non-uniformity coefficient KT/B, KW/L and KH/M were proposed and obtained. The results showed that the degree of contamination on top surface and leeward side is heavier than that on bottom surface and windward side. Thus, in the DC energized condition, contamination along the string is also non-uniform, and serious pollution occurs mainly in the high voltage terminal. In order to explain the uneven distribution phenomenon along the string, the coupling-physics model of composite insulator string was established and using the finite element method, the electric field around the insulator was simulated. Furthermore, basing on the field charging theory, the value of electric field force on particles around the insulator surface was calculated and the mechanism of non-uniformity along the insulator sting was then explained. The results are very important for guiding insulation design and field anti-pollution works.
TL;DR: In this paper, a geometric model of polymeric insulators was designed and studied using the finite element method as implemented in COMSOL multiphysics, and the results of the simulations showed that numerous parameters, such as the volume, number, and conductivity of the droplets, as well as their position with respect to the electrodes, affected the potential and electric field distribution.
Abstract: The main objective of this work is to study the behaviour of water droplets placed on a silicone surface in the presence of an electric field. We observed the effect of the water droplets on the distribution of the electric field and the voltage generated. A geometric model of the insulator was designed and studied using the finite element method as implemented in COMSOL Multiphysics. The results of the simulations showed that numerous parameters, such as the volume, number, and conductivity of the droplets, as well as their position with respect to the electrodes, affected the potential and electric field distribution. Furthermore, the simulations show that discharges caused by water droplets on the surface of polymeric insulators affect the long-term reliability of the component by lowering the surface hydrophobicity, boosting surface discharges.
TL;DR: In this article, the leakage current and its harmonic spectrum on clean and polluted 500-kV string insulators are determined under normal condition and lightning strokes, and the relation between back flashover and insulator surface condition are discussed under different magnitude of lightning strokes.
TL;DR: In this article, a charge transport model based on ion drift in gases of strong electron affinity has been studied in details and validated against experimental results in air and SF 6 at different pressure and voltage levels.
Abstract: A charge transport model based on ion drift in gases of strong electron affinity has been studied in details and validated against experimental results in air and SF 6 at different pressure and voltage levels. The size of the insulators also differs significantly. The choice of the model parameters, i.e. the solid and gas material properties, is carefully examined with information from existing literature. Results show that using the selected parameters, satisfactory agreement between predicted and measured potential distribution and surface charge density along the insulator surface can be obtained. Computational results for an 1100 kV epoxy spacer for use in HVDC wall bushing show that the concept of electrical conductivity as a material property is no longer valid in strong electric field for the gas surrounding the insulator. The polarity and density of the accumulated surface charge depend on the relative largeness of the electrical conductivity of the insulator material and the effective conductivity of the gas. The nonlinear effect due to ion generation and recombination becomes significant at very high voltage. The metallic cap providing shielding to the triple junction at the high voltage end of the insulator can induce much stronger local electric field near the insulator surface, by a factor of 1.48, if its shape is not optimized against the insulator geometry.
01 Mar 2018
TL;DR: In this paper, the change rule of insulator sheath hydrophobicity under the long-term operation condition, more than 390 samples produced by the same manufacturer that had operated for 3-22 years were extracted from the adjacent lines to eliminate the impact of the running environment and manufacturer formula.
Abstract: Due to excellent anti-pollution flashover performance, a composite insulator has become the most frequently and widely used insulator product in transmission lines
. Sheath hydrophobicity is the core factor that determines the anti-pollution flashover performance of the composite insulator. To study the change rule of insulator sheath hydrophobicity under the long-term operation condition, more than 390 samples produced by the same manufacturer that had operated for 3–22 years were extracted from the adjacent lines to eliminate the impact of the running environment and manufacturer formula. To study the reasons for hydrophobic fluctuations, surface energy tests and Fourier transform infrared spectroscopy tests were conducted on the superficial layer materials based on a two-droplet method. The change rule of the material physical and chemical properties with operation time was obtained. Next, the relationship between the surface microstructure of the material and operation time was determined by laser scanning confocal microscopy and scanning electron microscopy
. Finally, based on the analysis results of surface energy and surface topography, the physical model of shed material hydrophobic variation in the operation process was obtained.
TL;DR: In this paper, the fabrication and characterization of fully solution-processed flexible Metal-Insulator-Semiconductor (MIS) diodes are presented. The MIS structure was fabricated using aluminum doped zinc oxide and spin-on glass as semiconductor and insulator, respectively.
TL;DR: The feasibility of a permittivity-graded epoxy insulator with a low coefficient of thermal expansion (CTE) was clarified by evaluating the dielectric and thermomechanical properties of TiO2/SiO2 epoxy composites as mentioned in this paper.
Abstract: The feasibility of a permittivity-graded epoxy insulator with a low coefficient of thermal expansion (CTE) was clarified by evaluating the dielectric and thermomechanical properties of TiO2/SiO2 epoxy composites, which were epoxy composites co-filled with TiO2 and SiO2 particles. Upon varying the filling ratio of TiO2 to SiO2 while keeping the total filler volume constant, the relative permittivity of the TiO2/SiO2 epoxy composites varied in the range of 3.5–7.5 in our experiment while the CTE remained similar to that of an aluminum conductor used in gas-insulated power apparatus. The range of the relative permittivity of the TiO2/SiO2 epoxy composites with a low CTE satisfied the condition for realizing a permittivity-graded epoxy insulator. The application of an appropriate gradient of the permittivity distribution to a permittivity-graded epoxy insulator with a low CTE resulted in the relaxation of the electric field on the surface of an insulator.
TL;DR: In this paper, the authors discuss the problem of insulator flashover, which occurs when soluble and/or non-soluble contaminants cover the insulator surface which results in a reduction of the surface resistance.
Abstract: Insulator flashover happens when soluble and/or non-soluble contaminants cover the insulator surface which results in a reduction of the surface resistance. Significant research has been conducted ...
TL;DR: In this article, the development of low current arcs is classified in three stages: a formative leakage current phase (∼μΑ), a stage where discharges occur but are unstable with each half power cycle ( 1 mA).
Abstract: Low current arcs in the range 0.5 ∼5 mA occur in power networks in situations such as on overhead line insulators and cable terminations. These arcs are important because of their potential contribution to surface ageing, asset failure and potential flashover. In this paper, the development of low current arcs is classified in three stages: a formative leakage current phase (∼μΑ), a stage where discharges occur but are unstable with each half power cycle ( 1 mA). Arc resistance is a key element in controlling arc behavior in each stage, and is modeled as the combination of a stable arc resistance, an oscillating resistance and a surface resistance. The resulting arc model has been developed in PSCAD/EMTDC, to simulate an arc/discharge in each development stage. Simulations compare well with experimental data. The simulation reveals that peak arc current plays a key role in the transition from an unstable to stable arc. Analysis shows a significant increase in discharge energy as a result of its stabilization. These models explain the conditions required for accelerated ageing of polymeric insulators and can be used to design and interpret testing regimes, and for polymeric insulator asset management.
TL;DR: The designed DC electric cloaks succeed in providing DC electric invisibility of an electrical insulator in DC flow; specifically, an electric potential distribution is found that closely reproduces a distribution when no insulator is present.
Abstract: Based on the covariance matrix adaptation evolution strategy (CMA-ES), advanced designs of direct-current (DC) electric cloaks composed of bulk isotropic materials are presented through a topology optimization using a level set method. The designed DC electric cloaks succeed in providing DC electric invisibility of an electrical insulator in DC flow; specifically, an electric potential distribution is found that closely reproduces a distribution when no insulator is present. To produce this invisibility, we minimized the difference between distributions for the DC electric cloak and one without insulating obstacles as the objective function. CMA-ES explores optimal sets of level set functions as design variables that minimize the objective function with a perimeter constraint. In the best case in our simulation, the minimized objective function under cloaking reaches 0.00194% of that in the absence of cloaking. Toward multidirectional DC electric cloaks, a topology optimization subject to four-axial structural symmetries is demonstrated.
01 Oct 2018
TL;DR: An algorithm that detect the insulators' self-detonation defect based on deep learning reaches more than 99%, and the intelligent design effectively improves the efficiency of the power transmission system.
Abstract: Insulators are exerting an important influence in transmission lines. The timely detection of insulator explosion defects is an important guarantee for the safe operation of power systems. This paper puts forward an algorithm that detect the insulators' self-detonation defect based on deep learning. First, a Faster R-CNN target detection network is used to quickly classify and locate the insulators on the transmission lines. Then, a semantic segmentation to the located insulators is carried out by constructing a full convolutions neural network. In the end, the finished insulator image is input into the classification network to judge whether the insulator is burst. The experimental results show that the accuracy of insulator fault explosion recognition based on deep learning reaches more than 99%, and the intelligent design effectively improves the efficiency of the power transmission system.
TL;DR: In this paper, the surface flashover on the plane insulator-vacuum interface perpendicular to parallel electrodes is simulated by a Particle-In-Cell method using an external circuit model and a gas desorption model.
Abstract: With the introduction of an external circuit model and a gas desorption model, the surface flashover on the plane insulator-vacuum interface perpendicular to parallel electrodes is simulated by a Particle-In-Cell method. It can be seen from simulations that when the secondary electron emission avalanche (SEEA) occurs, the current sharply increases because of the influence of the insulator surface charge on the cathode field emission. With the introduction of the gas desorption model, the current keeps on increasing after SEEA, and then the feedback of the external circuit causes the voltage between the two electrodes to decrease. The cathode emission current decreases, while the anode current keeps growing. With the definition that flashover occurs when the diode voltage drops by more than 20%, we obtained the simulated flashover voltage which agrees with the experimental value with the use of the field enhancement factor β = 145 and the gas molecule desorption coefficient γ=0.25. From the simulation results, we can also see that the time delay of flashover decreases exponentially with voltage. In addition, from the gas desorption model, the gas density on the insulator surface is found to be proportional to the square of the gas desorption rate and linear with time.
12 Sep 2018
TL;DR: In this article, electrical, physical and mechanical properties of glass fiber reinforced polymer (GFRP) composites including acid absorption, breakdown voltage, and tensile strength have been investigated in order to be used as insulators in power transmission lines.
Abstract: Recent developments in applying composites in different industries result in replacing traditional materials with them Polymer matrix composites have become one of the most popular advanced materials in the industries due to their peculiar properties, appropriate cost, and various and easy manufacturing methods In this project, electrical, physical and mechanical properties of glass fiber reinforced polymer (GFRP) composites including acid absorption, breakdown voltage, and tensile strength have been investigated in order to be used as insulators in power transmission lines In order to identify the chemical structure of neat resins and their composites, and also determining the possibility of bonding between polymer and glass, Fourier Transform Infrared Spectroscopic (FTIR) test was conducted Regarding high voltage tests, a direct correlation was found between the amount of absorbed moisture by the specimens and the amount of breakdown voltage The composites were degraded because of exposing, and this behavior was verified by Scanning Electron Microscopy (SEM) and Atomic Absorption Spectrometry (AAS) analysis The results indicated a drop of 253% and 283% in tensile strength for E-glass epoxy and polyester composites with acid aging, respectively Also, the breakdown voltage declined to 32 and 21 kV mm−1 after the moisture content reached 01% and 027% for E-glass epoxy and polyester composites, respectively It can be concluded that epoxy matrix composite is more resistant to acid exposure compared to polyester matrix composite and is more suitable to be used in power transmission lines
TL;DR: In this article, a simulation model combining both the plasma hydrodynamics and charge trapping-detrapping process was built to study the mechanism of surface charge accumulation in HV power equipment with gas-solid insulation.
Abstract: Most of the HV power equipment with gas-solid insulation suffers a lot from the surface charge accumulation due to corona discharge. The existence of surface charge distorts the local electric field and leads to surface flashover faults in extreme situations. As a result, it is important to figure out the mechanism of surface charge accumulation process. In this study, a simulation model combining both the plasma hydrodynamics and charge trapping-detrapping process was built. The simulation results have a good agreement with the experimental data, the main summary is as follows: in the surface charge accumulation process, the corona discharge intensity increases first and then decreases with time. The curves of the surface potential distributions have different shapes at different times, the central value goes up rapidly with time in the beginning and finally reaches saturation. Surface charges exist in the skin layer of epoxy insulator, some of them may be captured by traps while transporting away under built-in electric field.
TL;DR: A triple-point-junction shield electrode is designed which minimizes the electric field at the delicate insulator-metal-vacuum interface and linearizes the potential across the insulator, thus reducing the risk of arcing along the ceramic insulator.
Abstract: Nuclear physics experiments performed at the Continuous Electron Beam Accelerator Facility (CEBAF) at the Jefferson Lab require a DC high voltage photogun to generate polarized electron beams from GaAs photocathodes. The photogun uses a tapered ceramic insulator that extends into the vacuum chamber and mechanically holds the cathode electrode. Increasing the operating voltage from nominal -130 kV to -200 kV will provide lower beam emittance, better transmission through injector apertures, and improved photocathode lifetime. This desire to increase the photogun operating voltage led to the design of a triple-point-junction shield electrode which minimizes the electric field at the delicate insulator-metal-vacuum interface and linearizes the potential across the insulator, thus reducing the risk of arcing along the ceramic insulator. This work describes the results obtained using COMSOL® electrostatic-field simulation software and presents the high voltage conditioning results of the upgraded -200 kV CEBAF photogun.
TL;DR: In this article, a measurement circuit was used to measure the partial surface conductivity of algae and non-algae dots on insulator surfaces and an image processing method was proposed to calculate the algae coverage rate.
Abstract: In recent years, microorganisms such as algae have been found on composite and RTV coated insulators in humid environment in southwest and southern China. Algae growth poses a potential threat to the outer insulation of electrical power system because of the special features of biological foul. Insulator samples with algae growth were obtained from transmission towers of 500 kV Tianguang DC transmission line and the influence of algae growth on the external insulation performance was studied in this paper. A measurement circuit was used to measure the partial surface conductivity of algae and non-algae dots on insulator surfaces. Water spray classification method was used to test the hydrophobicity of algae and non-algae parts of the insulators. An image processing method was proposed to discern algae on the insulator surfaces and calculate the algae coverage rate. The withstand capability of insulator were tested at working voltage and 1.2 times working voltage. The research results showed that the presence of algae increased the local salt distribution and reduced the hydrophobicity of insulator surfaces. The results also indicated that impacts of algae contanmination to withstand capability of insulators were limited when the algae coverage rate was less than 20%.