Insulation characteristics of triple mixtures of c-C_4F_8/N_2/CO_2 under lightning impulse voltage

This paper has researched the insulation characteristics of 10% c-C4F8/N2/CO2 mixtures under lightning impulse voltage by experiment. It is shown that the positive and negative lightning impulse breakdown voltages of 10%c-C4F8/N2/CO2 gas mixtures rise linearly as the electrode gap distance and gas pressure increase and under the same conditions, the positive lightning impulse breakdown voltage of the gas mixtures is always higher than the negative lightning impulse breakdown voltage. As the gas mixtures have a little higher liquefied temperature than SF6 and the comprehensive GWP is about 5% of SF6, and the positive and negative lightning impulse breakdown voltages can both reach 60% of SF6, 10%c-C4F8/N2/CO2 gas mixtures can be applied as insulation gas in electrical equipment such as C-GIS, GIT, GIL and so on.

Surface Partial Discharge Characteristics of Oil-paper Insulation Under Combined AC-DC Voltage

The valve side windings of converter transformers bear AC, DC, impulse, and reversal-polarity voltages during operation, which could result in serious insulation problems of the equipment. By performing experiments with surface discharge model of oil-paper insula- tion at 80 ℃ under combined AC-DC voltage for 200 h, we studied the spectrums and statistical parameters of partial discharges at different discharge stages. Furthermore, some fingerprint parameters were calculated in order to estimate the development situation of par- tial discharge, while the characteristic gases dissolved in the transformer oil were measured by gas chromatography. The surface discharges in the experiments were observed using a high speed camera, and a full discharge process could be marked off into four stages as follows. ①The elementary stage. When a partial discharge occurs near electrodes, electrical charges are injected into the region near electrodes and causing bubble generation. ②Due to their high resistivity and low dielectric constant, the bubbles would bare the major part of the voltage applied to samples. Therefore, discharge happens inside the small bubbles, and it emits a lot of light. ③Micromolecules of gas are produced in discharge, and further ionization in the transformer oil takes place simultaneously when high-energy electrons collide with oil molecules. ④The carrier charge moves forward to electrodes driven by the applied electric field, till they neutralize with the charge from electrodes, and hence discharge channels are formed subsequently.

Study on Intermittent Discharge Characteristics of Typical Solid Insulation Defects in Gas Insulated Switchgear

In response to the problem of frequent leakage and false alarm of partial discharge insulation defects in GIS,this paper conducts experimental research on intermittent discharge characteristics of common solid insulation defects in GIS.Using true GIS to build amulti-source testing platform for intermittent discharge of solid insulation defects,and using pulse current method,ultra-high frequency method,ultrasonic method,and gas characteristic component detectionmethod to study the variation law of intermittent discharge characteristics of solid insulation defects.The results showthat:the intermittent discharge state of metal fouling defects on the solid insulation surface decreases with the extension of the discharge time,the discharge time interval as a whole shows an increasing trend,and the metal fouling defects on the solid insulation surface in the intermittent discharge state is difficult to develop into a breakdown discharge fault.The overall discharge amount of air gap defects inside solid insulation also shows the law of increasing first and then decreasing,and the discharge amount of air gap defects inside solid insulation stays at a large level for a long time during intermittent discharge,and there is a risk of breakdown,and the discharge will gradually evolve into continuous discharge;ultrasonic method and characteristic component detection method cannot realize the effective perception of intermittent discharge of metal fouling.The 50-period mapping information commonly used in the power field cannot reflect the intermittent discharge variation law of solid insulation,and the 200-period UHF mapping composed of four groups of 50-period UHF mapping data can initially derive the intermittent discharge distribution law of solid insulation defects.The research results of this paper are of great significance to expand the knowledge of intermittent discharge characteristics and the detection of GIS discharge defects in the field.

Impact of the Insulator on the Electric Field and Generation Characteristics of Vacuum Arc Metal Plasmas

The field electron emission plays a vital role in the process of vacuum discharge breakdown. The electric field strength at the cathode tip is significant to the generation char- acteristics of vacuum arc metal plasmas. To increase the field strength at the cathode tip, a coaxial electrode plasma source was employed with an insulator settled between the electrodes. The math expression of the field strength is derived based on the Gauss theory. The impact of the insulator on the electric field and parameters of plasmas were investigated by MAXWELL 3D simulation software and the Langmuir probe. In addition, a composite insulator was adopted to further strengthen the field strength. A series of experiments were performed to focus on the role of the composite insulator in detail. The experimental and simulation results indicate that, a reasonable layout of the insulator, especially the composite insulator, can effectively increase the field strength at the cathode tip and the plasma density.

Influence of spacer insulator material temperature characteristics on its electric properties

Spacer insulators are important insulating component of gas insulated switchgear(GIS). In order to analyze the influence of spacer insulator materials temperature characteristics on the electric performance, we tested the temperature distribution under work condition and the temperature characteristics of the material's relative permittivity. Then established a spacer insulator simulation model in finite element numerical simulation software to calculate its temperature and electric field. Using the temperature test results as a reference to verify the temperature calculation, and in order to analyze changes of the electric field along the surface of the spacer insulator, the temperature characteristics of relative permittivity have to be considered. Through the experimental research and simulation analysis, we found that the temperature characteristics of the spacer insulator materials have great impacts on the spacer insulator performance. When the temperature increases, the material relative permittivity also increases. In the low-temperature region of spacer insulator, the electric field intensity along the surface increases, so the electrical performance deteriorates. The conclusion of this paper can provide an important reference for further research about spacer insulator's working performance analysis.

Comprehensive simulation of snow crystal deposition and electric field characteristics of composite sheath improved porcelain cantilever insulator in a wind and snow environment

The installed porcelain insulators on existing railway lines in China are prone to“snow flash”in winter.In order to prevent the occurrence of“snow flash”and improve the reliability of the insulators,a composite-porcelain insulator is designed.A multi-physics coupling simulation model is built based on numerical simulation methods of the electromagnetic field theory and computational fluid dynamics.Taking average electric field intensity on the surface of the insulator as the characteristic parameter of the electric field distortion degree and the snow crystal collision coefficient and distribution coefficient as the characteristic parameter of snow crystal deposition,the characteristics of snow crystal deposition under different wind speeds and wind direction angles and the electric field characteristics under two snow cover types are analyzed.The simulation results show that the average electric field intensity of composite-porcelain insulators is 10.4%and 13.8%,respectively,lower than that of porcelain insulators in vertical and horizontal wind snow covers,which can effectively reduce the degree of electric field distortion.The collision coefficient of snow crystals on the surface of the composite-porcelain insulator sheds is 16.0%higher than that of the porcelain insulator,and the collision coefficient of the trunk and the fittings are lower 20.2%and 11.9%than that of the porcelain insulator.There is almost no change in the distribution coefficient of the insulator sheds.

Electrical characteristics of SiGe-on-insulator nMOSFET and SiGe-silicon-on-aluminum nitride nMOSFET

This paper investigates the electrical characteristics and temperature distribution of strained Si/SiGe n-type metal oxide semiconductor field effect transistor （nMOSFET） fabricated on silicon-on-aluminum nitride （SOAN） substrate. This novel structure is named SGSOAN nMOSFET. A comparative study of self-heating effect of nMOSFET fabricated on SGOI and SGSOAN is presented. Numerical results show that this novel SGSOAN structure can greatly eliminate excessive self-heating in devices, which gives a more promising application for silicon on insulator to work at high temperatures.

Influence of Electrical Field Distortions Induced by Water Droplets on the Contamination Characteristics of an Insulator

When separated water droplets condense on the surface of a composite insulator,the electrical field on the insulator surface is distorted.In turn,such distortions change the trajectories of pollution particles.In this study,the COMSOL software is used to simulate such a process for the FXBW4-10/100 composite insulator with or without water droplets condensation under a 10 kV DC voltage.The influence of the wind speed and particles concentration on the contamination characteristics of the considered 110 kV insulator is analyzed.The results show that:1)in the presence of water droplets on the insulator surface,the ratio of electrical field force and gravity acting on the particles is large;2)the contamination on the insulator surface increases with the wind speed;3)when the wind speed is small,the relationship between the contamination amount and the pollution concentration is essentially linear.

The electrical characteristics of a 4H-silicon carbide metal-insulator-semiconductor structure with Al_2O_3 as the gate dielectric

A 4H-silicon carbide metal-insulator-semiconductor structure with ultra-thin Al2O3 as the gate dielectric, deposited by atomic layer deposition on tile epitaxial layer of a 4H-SiC （0001） 80N-/N＋ substrate, has been fabricated. The experimental results indicate that the prepared ultra-thin Al2O3 gate dielectric exhibits good physical and electrical characteristics, including a high breakdown electrical field of 25 MV/cm, excellent interface properties （1 × 10^14 cm^-2） and low gate-leakage current （IG = 1 × 10^-3 A/cm 2@Eox = 8 MV/cm）. Analysis of the current conduction mecha- nism on the deposited Al2O3 gate dielectric was also systematically performed. The confirmed conduction mechanisms consisted of Fowler-Nordheim （FN） tuaneling, the Frenkel-Poole mechanism, direct tunneling and Schottky emission, and the dominant current conduction mechanism depends on the applied electrical field. When the gate leakage current mechanism is dominated by FN tunneling, the barrier height of SiC/Al2O3 is 1.4 eV, which can meet the requirements of silicon carbide metal-insulator-semiconductor transistor devices.

Aging Characteristics and Influencing Factors of the Sheds of Composite Insulators in Karst Regions of China

In recent years,more and more high-voltage overhead transmission lines were built passing through the karst regions in southwestern China.This type of special landform seems to have an adverse effect on the aging of the sheds of the line suspension composite insulators,which may lead to unexpected flashover and line tripping.In order to find out the particularity of the aging characteristics of insulators operating in the karst regions,samples in operation were selected from both the karst regions and the flatlands.Hydrophobicity,amount of surface contamination,and contaminant composition of the sheds were studied,then a comparison of performance between the two was made,and the possible influencing factors that cause such differences were discussed.The results show that the overall aging of the sheds of the composite insulators operating at the karst regions is more aggravated,which is caused by the combined influence of factors including the special topography,climate,and pollution in the area.The strong wind crossing the col will bring about the mutual scraping on the edges and stress concentration at the root of the sheds,leaving scratches and root cracks;the infiltration from these rupture of acid liquid,if any,will accelerate the aging and corroding of the internal silicone rubber material;moreover,the carbonates enriched on the surface of the sheds will gradually transform into more corrosive sulfates in an acidic environment,leading to further deterioration and chalking of the sheds of the insulators.The research work in this paper can provide guidance for the current operation and maintenance of composite insulators in the karst areas,as well as having important reference values for the layout design and insulation configuration of transmission lines to be built across karst landforms in the future.

Numerical Simulation of Contamination Accumulation Characteristics of Composite Insulators in Salt Fog Environment

To investigate the fouling characteristics of the composite insulator surface under the salt fog environment,the FXBW-110/120-2 composite insulator was taken as the research object.Based on the field-induced charge mechanism,the multi-physical field coupling software COMSOL was used to numerically simulate the fouling characteristics,explored the calculation method of ESDD,and demonstrated its rationality.Based on this method,the pollution characteristics of the composite insulator under the pollution fog environment were studied,and the influence of wind speed,droplet size,and voltage type on the pollution characteristics of the composite insulator was analyzed.The results showed that:with the increase in wind speed,the amount of accumulated pollution of insulator increases in the range of droplet size,and the relationship between wind speed and accumulated pollution is approximately linear;at the same wind speed,the amount of accumulated pollution increases with the increase of droplet size under the action of DC voltage;when there is no voltage,the amount of dirt on the upper surface of the insulator is more than that on the lower surface,while it is the opposite under DC voltage.

Generation characteristics of a metal ion plasma jet in vacuum discharge

To improve the performance of a metal ion plasma jet in vacuum discharge, an anode-insulated cone-cylinder electrode with insulating sleeve is proposed in this paper. Discharge characteristics and generation characteristics of plasma of the electrode are investigated, effects of diameter of insulating sleeve, variety of cathode material and length of the insulating sleeve on characteristics of metal ion plasma jet are discussed. Results indicate that a directional and steady plasma jet is formed by using the novel electrode with insulating sleeve under high vacuum conditions. Moreover, the properties of metal ion plasma jet are improved by using the aluminum cathode and thin and long insulating sleeve. The study provides strong support for research of vacuum metal ion plasma thruster and ion implantation technology.

Research on Propagation Characteristics of XLPE Cable Electrical Trees in different Electrode System

The electrical tree discharge channel will be formed at concentrate spot of electric field in solid insulation dielectric,in order to study the difference of electrical tree under different electrical field,the short-cable electrode system with actual XLPE cable was designed,experiments were performed under 12 kV,15 kV,18 kV,21 kV compare to the needle-plate electrode system.Experiment results show that the electrical tree of short-cable electrode system have the same growth trend with the needle-plate electrode system in the growing characteristic,the dense of electrical tree increase with the increase of voltage level,electrical tree of short-cable electrode system growth is slower than the needle-plate electrode system at the same voltage;To get the same shape of electrical tree,the voltage of short-cable electrode system must be higher than needle-plate electrode system,the results show that the semiconductor layer and the copper shield layer outside of XLPE cable have very important affection on the electrical trees degradation.

Flashover Characteristics of Flat Plate Model Under DC Voltage in Wind-sand Condition

The influence of sand dust on discharge of external insulation has caused widespread concern.At present,the research results show wind-sand electricity has a remarkable effect on the discharge characteristics of insulator and has little influence on the discharge characteristics of air gap.The flashover of insulator strings occurs along the insulator surface and air gaps,and the sand dust deposited on the insulator surface may affect the flashover characteristics of insulator strings.This paper studies the flashover characteristics of flat plate model under DC voltage in wind-sand condition.The experimental results show that under positive polarity voltage,the flashover voltage of the flat plate model has a maximum value,while under negative polarity voltage,the flashover voltage of the flat plate model has a minimum value with a certain degree of sand dust deposition.The wind or sand in sand-dust weather has an important effect on the flashover characteristics of the flat plate model.In certain variation range of electric charge,electric charge of sand dust has little effect on the flashover voltage of flat plate model under DC voltage.The deposition of sand has significant influence on the flashover process of flat plate model,which is related to the deposition density and moisture content of sand particle.

Influence of Repetitive Impulse Waveforms on Surface Discharge Characteristics and Insulation Life for Polyimide Film

Accelerated insulation aging problems under high frequency repetitive impulses in power electronic transformers are drawing more and more attention in modern power systems. Partial discharge (PD) characteristics including discharge inception voltage, phase distribution and statistical characteristics on polyimide (PI) surface under different impulse waveforms and the insulation life of PI films are studied in this paper. We carry out experiments based on PD and insulation lifetime test systems, using five different types of repetitive impulses, including three bipolar waves and two unipolar waves. The experimental results show that there is little variation in discharge inception voltage under different waveforms, but great variation in phase distribution and statistical characteristics of PD. In addition, insulation life is approximately the same under different waveforms with the same polarity, and the aging rate under bipolar waveforms is larger than that under unipolar waveforms. We explain the differences between the bipolar and unipolar waveforms on insulation life, which can be concluded that the surface charge under unipolar waveform accumulates more significnatly compared with bipolar waveform and decreases the electric filed strength in discharging the air gap and inhibits surface discharge from occurring.

GIL三支柱绝缘子表面电荷积聚特性

表面电荷积聚特性主要集中在平板试样、盆式绝缘子,对GIL设备用三支柱绝缘子表面电荷积聚特性鲜有报道。文中以实际550 kV GIL三支柱绝缘子为试品,建立三支柱绝缘子三维测量试验平台,采用电容探头法,改变电压幅值、加压时间、粗糙度,试验获取三支柱绝缘子表面电荷积聚规律。结果表明:交流电压作用下GIL三支柱绝缘子支柱区域积聚的电荷密度较小,而腹部区域积聚的电荷密度较大;提高试验电压幅值、延长试验电压作用时间、增大支柱绝缘子表面粗糙度,均可增加GIL三支柱绝缘子表面电荷密度;一定条件下,交流电压下随着表面电荷的积聚,500 kV三支柱绝缘子沿面闪络电压减小约9.6%。文中研究可为GIL设备三支柱绝缘子设计优化及设备运维提供一种解决问题的思路。

限域结构热致变色相变环氧复合绝缘陷阱特性的机理

热致变色相变复合绝缘在电热激励下能实现一系列先进功能,已广泛应用于大量智能电气与电子设备中.然而热致变色相变复合绝缘存在限域结构,无法通过现有的纳米复合界面模型分析其电荷陷阱特性,导致其在电热耦合应力下的介电可靠性提升缺乏科学依据.本文通过等温表面电位衰减(ISPD)、开尔文探针力显微镜(KPFM)等方法,研究了热致变色相变环氧复合绝缘的电荷陷阱特性与机理.结果表明:30℃和70℃下限域结构对热致变色相变环氧绝缘陷阱特性的影响趋势相反,可能源于限域相变或限域界面的影响.理论分析发现,限域相变对陷阱温度特性的影响规律与实验结果不符,并非影响陷阱温度特性的主要原因.通过KPFM原位表征直接验证了限域界面内存在势垒,且起源于接触起电机制.限域界面接触起电电荷量随温度的变化会影响限域界面势垒高度,是影响陷阱温度特性的主要原因.

考虑气隙缺陷与介电功能梯度材料的GIS盆式绝缘子电场特性研究

气隙缺陷是GIS盆式绝缘子内部常见的缺陷之一,气隙会引起电场畸变,而介电功能梯度材料的引入可以优化盆式绝缘子的局部电场,但在气隙缺陷与介电功能梯度材料共同作用下,其电场特性尚未可知。因此,本文建立具有均匀介质和介电功能梯度材料(ε-FGM)的GIS盆式绝缘子电场仿真模型,讨论气隙的存在及气隙位置对于均匀介质和ε-FGM盆式绝缘子电场分布的影响。结果表明:引入的介电功能梯度材料的调控效果较为理想。当均匀介质盆式绝缘子中掺杂气隙时,靠近高压导体、绝缘子中部、靠近接地外壳3个气隙位置的场强均有明显的增加,电场增加率分别为85.32%、78.10%和68.69%。气隙缺陷对ε-FGM盆式绝缘子电场特性影响趋势基本和对均匀介质盆式绝缘子的影响趋势一致,但从具体数值上看,气隙缺陷对ε-FGM盆式绝缘子电场特性影响与对均匀介质盆式绝缘子的影响仍有一定的差异性。气隙缺陷对于介电功能梯度材料绝缘子电场值的影响更大,在设计介电功能梯度材料绝缘子时,应尤其注意对介质中气隙缺陷的抑制。