Dynamics of metallic particle contaminants in GIS withdielectric-coated electrodes

Electrical insulation performance of compressed gas insulated switchgear (GIS) and gas insulated transmission line (GITL) systems is adversely affected by metallic particle contaminants. Dielectric coatings applied to the inside surface of the outer enclosure of a coaxial GIS/GITL system improve the insulation performance in several ways. Coating has the effect of smoothing the electrode surface and reducing the prebreakdown current in the gas gap. Also, the electrostatic charge acquired by a particle is reduced and hence the range of its motion under an applied power frequency field is inhibited. The movement of such particles is complex and dependent on several parameters. In this paper the dynamics of wire particles in a coaxial system under AC voltage is studied when the inside surface of the outer enclosure of a coaxial GIS/GITL system is coated with a high resistance material. Suggestions for reducing the particle excursion in GIS/GITL systems are discussed     

特高压GIS隔离开关操作时其壳体电压暂态特性仿真分析

特高压(UHV)系统电压等级高、容量大,电磁暂态问题相当严重。为研究特高压气体绝缘变电站(GIS)在隔离开关操作时壳体电压的暂态特性,从而对今后特高压变电站的建设及绝缘配合问题提供参考建议,结合我国某1 100kV特高压气体绝缘变电站的具体情况,分析了特高压下GIS暂态壳体电压(TEV)的计算原理,利用多导体传输线模型计算了壳体各处的TEV,并对其进行了频谱处理。最后,分析了隔离开关的操作方式、操作相别、接地方式等对暂态壳体电压的影响。仿真结果表明:隔离开关操作方式不同时,暂态壳体电压最大值出现的位置不同;在GIS出线段,由于布置的对称性使得暂态壳体电压幅值也具有对称性。     

气体绝缘开关设备中特快速瞬态过电压研究的新进展

气体绝缘开关设备（gas insulated switchgear,GIS）中的隔离开关操作空载短母线会产生陡波前、高幅值的特快速瞬态过电压（very fast transient overvoltage,VFTO）、瞬态壳体电位和电磁干扰,对GIS及其连接的具有绕组的设备、与壳体连接的二次设备绝缘产生危害,干扰二次设备工作,严重影响设备的安全运行。对2009年前国内外在VFTO测量方法、特性试验、数字仿真和对绝缘影响以及外部VFTO方面的研究状况进行了综述。概要总结了国家电网公司在特高压GIS中VFTO实测及仿真研究方面取得的新进展,提出了特高压GIS中VFTO需要深化研究的内容,即重点关注VFTO的传播特性与仿真建模,VFTO下的绝缘特性和机制研究,以期全面掌握特高压GIS中VFTO特性,对特高压输变电设备的研制、工程设计和运行提供依据和有益的参考。     

Charging and behavior of a spherically conducting particle on a dielectrically coated electrode in the presence of electrical gradient force in atmospheric air

This paper discusses the charging and behavior of a spherically conducting particle on a dielectrically coated electrode in non-uniform dc and ac electric fields between non-parallel plane electrodes in atmospheric air. The charging mechanism of a particle resting on a dielectrically coated electrode is investigated by observing light emissions from partial discharges and by utilizing the dust figure technique. The charge acquired by a particle is estimated from the results of particle motion onset voltage measurement and direct measurement with a Faraday cage. The basic particle movement as well as particle-triggered breakdown characteristics under non-uniform electric field distribution along the electrode surface is also investigated. The results suggest that the effect of the electrical gradient force/dielectro-phoretic force on particle motion on a dielectrically coated electrode should be adequately considered in the design of gas insulated systems (GIS). This is because a particle can move laterally on the coated electrode toward increasing electric field regions by the action of the electrical gradient force which is independent of the charge on the particle. Also the possibility of the particle charging and lifting at high field regions or reaching and adhering onto an insulating spacer further increases the risk of breakdown.     

Particle-triggered pre-breakdown phenomena in atmospheric air gap under AC voltage

Corona discharge mechanism and breakdown voltage characteristics of air gaps in the presence of metallic particles were investigated including the relationship between the corona discharge mechanism and the phase resolved partial discharge patterns. These results are of interest for detection of foreign particles in gas insulated systems (GIS). The results with different shaped particles show that the corona mechanism depends on the particle shape and applied voltage. Moreover the corona discharges on both sides of the particle interfere with each other by inflow of charge carriers into the particle. The breakdown voltage is a minimum when the particle is in the vicinity of the electrode due to active interference of coronas. The phase-charge characteristics as the phase resolved partial discharge patterns vary with the particle shape. This suggests that the corona discharge mechanisms for all types of particles should be considered in the particle-detection method for GIS based on the phase resolved partial discharge patterns.     

Development and design of DC‐GIS

In order to realize a reliable, compact, and economical converter station for HVDC transmission, applications of gas insulated switchgear (GIS) for dc transmission lines are considered. The characteristics of dc gas insulation differ from those of ac. The behavior of metallic particles left in the enclosure is one of the largest differences. The accumulation of electrical charges on solid insulators is another essential factor in designing a DC‐GIS. Also, degradation of metal oxide arrester blocks under dc stress must be deliberated. Based on the fundamental studies, we developed the components of ± 500‐kV DC‐GIS. Electrical and mechanical performances of these components have been tested and proven to be satisfactory. Finally these components have been assembled into a full DC‐GIS and subjected to a long‐term voltage endurance test. In this paper, the design philosophy of ± 500‐kV DC‐GIS, details of the components, and the test results are described. © 1999 Scripta Technica, Electr Eng Jpn, 129(2): 51–61, 1999     

Suppression of Metallic Particle Lift‐Off in GIS by a Nonlinear Resistivity Coating

To suppress metallic particle lift‐off in compact gas‐insulated switchgear (GIS), a coating with nonlinear resistivity characteristics was developed for the inner surface of the GIS tank. An electrical field analysis that measured the current density and electric field (J–E) characteristic indicates that a nonlinear resistivity coating can reduce field intensification at triple junctions between metallic particles and the coating, and can effectively suppress particle lift‐off. The results of experiments using a GIS mock‐up model indicate that a nonlinear resistivity coating increases the lift‐off electric field of metallic particles with less statistical dispersion than a dielectric coating.     

特高压交流试验示范工程GIS隔离开关带电操作试验

为验证我国特高压交流试验示范工程金属封闭开关设备(gas insulated switchgear,GIS)中隔离开关带电操作的安全性,在长治、南阳和荆门变电站对所有特高压GIS隔离开关进行了带电操作试验。在前期特高压GIS和复合型气体绝缘金属封闭开关设备(hypid gas insulated switchgear,HGIS)中特快速瞬态过电压(very fast transi-ent overvoltage,VFTO)实测研究基础上,开展现场典型运行方式下隔离开关带电操作,监测产生的VFTO和暂态壳体电位(transient enclosure voltage,TEV)。试验初步得出了特高压变电站实际VFTO和TEV水平及分布,结果表明:特高压GIS隔离开关的带电操作是安全的,但应注意产生的TEV对二次设备的影响,阻尼电阻能够有效抑制VFTO和TEV。带电操作试验的开展为今后特高压GIS隔离开关的带电操作提供了依据。     

一起363kVGIS充电闪络故障的原因分析

分析了一起363kVGIS充电时闪络故障的原因,提出了GIS交接试验中做交流耐压试验的同时应进行局部放电的测量,并在条件许可的情况下进行操作冲击电压试验,以避免如绝缘子伤痕和裂痕、自由微粒、悬浮电位和异物遗留在GIS内部等原因而造成GIS故障。     

Development of GIS fault location system using pressure wavesensors

This paper describes a series of development tests carried out when developing a GIS (gas insulated substation) fault location system using pressure wave sensors for a GIS with a main bus in which each gas section per bay is connected by gas piping. This paper also refers to the basic construction of the software of the fault location system actually applied to a GIS with a rated voltage of less than 168 kV     

Development of a GIS fault location system

This paper describes a series of development tests carried out when developing a fault location system applied for the main bus of GIS (gas‐insulated switchgear) by using shock pressure relays. In the main bus of this GIS, each gas section per bay is connected by gas pipings. This paper also refers to the basic construction of the software of the fault location system actually applied to GIS with rated voltage less than 168 kV. © 2000 Scripta Technica, Electr Eng Jpn, 131(2): 20–29, 2000     

直流气体绝缘输电线路的绝缘设计

气体绝缘输电线路(gas insulated transmission line,GIL)与架空线路相似但占地空间小、损耗低,在高压直流输电和特高压直流输电领域具有较大的应用空间。通过分析表面电荷和金属导电微粒对绝缘子沿面放电的影响,指出了绝缘子表面电荷积聚和自由金属导电微粒附着是降低直流GIL绝缘性能的重要原因。采用了使电场分布合理的方法,即半圆锥形盆式绝缘子的优化和表面电阻率阶梯分布的覆膜。设计了包括电极覆膜、微粒陷阱、驱赶电极和屏蔽环的直流GIL的绝缘结构。     

Motion behavior and deactivation method of free-conducting particle around spacer between diverging conducting plates under DC voltage in atmospheric air

This paper deals with free conducting particle motion around different shaped spacers between diverging conducting plates under DC voltage in atmospheric air. Spherical particle motion was observed experimentally and the results were discussed on the basis of the electrostatic force acting on the particle with and without spacer. The results show that a particle around a spacer tends to move laterally towards or away from the spacer towards higher field regions, depending on the spacer configuration. It lifts at higher field positions and sometimes adheres to the spacer. The effects of spacer angle and spacer material (permittivity) on free conducting particle motion are also discussed. For comparing the results obtained with a sphere, a wire particle motion around different shaped spacers is also investigated. The obtained results suggest one of the methods to prevent/suppress the conducting particle from approaching or adhering to spacers, is to reduce the field strength in the vicinity of the triple junction of gas, solid dielectric and electrode in gas insulated system (GIS).     

On-line detection and location of low-level arcing in dry-typetransformers

This paper describes the development of a microprocessor based system, based on four different physical phenomena, for reliable and accurate detection and location of arcing in dry-type transformers. The proposed technique was tested for actual arcing, generated on a 15-kVA, 230/115-V Y/Δ transformer enclosed in a 30" × 30" × 21" metallic enclosure. Some results showing the performance of the detection and location system are presented in the paper. The technique can be applied to detect arcing in metal-clad low-voltage/medium voltage switchgear, drives, gas insulated switchgear (GIS), generator bus-ducts, and other metal-clad electrical apparatus against arcing     

Electric field effect on metallic particle contamination in a common enclosure gas insulated busduct

Sulphur hexaflouride (SF₆) is generally found to be very sensitive to field perturbations such as those caused by conductor surface imperfections and by conducting particle contaminants. A study of CIGRE group suggests that 20% of failures in gas insulated substations (GIS) is due to the existence of various metallic contaminations in the form of loose particles. The presence of contamination can therefore be a problem with gas-insulated substations operating at high fields. If the effects of these particles could be eliminated, then this would improve the reliability of compressed gas insulated substation. It would also offer the possibility of operating at higher fields to affect a potential reduction in the GIS size with subsequent savings in the cost of manufacture and installation. The purpose of this paper is to develop techniques, which will formulate the basic equations that will govern the movement of metallic particles like aluminum and copper in a bus duct. The simulation considers the electric field effect on particle movement and the results have been presented and analyzed     

Discharges from moving particles in GIS [gas-insulated switchgear]

The study of the motion of moving metallic particles in GIS requires a good knowledge of the carried charge of the particle. In this paper, measurements of the charging process of a moving particle, performed in a realistic single-phase GIS, are presented. By measuring the charge impulses and the voltage phase at consecutive impacts, it is possible to estimate the carried charge and then compare the results with the existing models of the particle charge. Also, besides the discharges from in-flight corona reported by several authors, it is shown that, for higher voltage levels, several discharges between the particle and the enclosure (outer electrode) can occur as the particle impacts with the enclosure     

Motion and size estimation of a free moving metallic particle in GIS based on propagation properties of acoustic waves

We have investigated the propagation properties of Lamb waves and motion characteristic of free moving metallic particle in a gas‐insulated switchgear (GIS) tank to diagnose the insulation performance of GIS. We have proposed a new identification technique for defect location in GIS based on the time–frequency analysis of the Lamb waves using the Wavelet Transform. In this paper, we measured the acoustic signals excited by a metallic particle colliding with the tank sheath. Furthermore, we measured the moving particles under a high electric field in GIS using a high‐speed video camera. As a result, we examined the relationship between maximum lifting height and the flight time during subsequent impacts of a moving particle. Moreover, we estimated particle size based on the propagation properties of Lamb waves. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 150(1): 26–33, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20023     

Dynamic analysis of motion of spherical metallic particles in non-uniform electric field

This paper presents a theoretical analysis of the dynamics of motion of spherical metallic particles under non-uniform fields for direct-current gas-insulated switchgear (dc GIS) and for electrostatic separators/sizers (ESS). The particle equations of motion between a pair of diverging conducting plates are numerically solved in three dimensions using a computational algorithm. The upper plate is energized by HV dc or HV ac of variable frequency, while the lower one is grounded. In the case of ESS, the lower electrode is also mounted horizontally on a vibratory conveyor. The results reveal that the particle exhibits several phenomena during motion depending on its initial position, radius and density, angle between the diverging plates, tilt angle of the electrode system, and frequency and amplitude of the applied voltage. The influence of vibratory-conveyor variables on the separation/sizing process is studied in the light of the particle trajectory in the third dimension. Moreover, the results are interpreted using dimensional analysis. The use of HV ac causes the separation/sizing process to be imprecise; the higher the applied-voltage frequency and the larger the particle radius, the higher is the risk of breakdown. Depending on the tilt angle and orientation of the earthed electrode relative to the divergent angle between the electrodes, particle trapping can be helped or hindered. Therefore, several factors should be taken into consideration in the design and installation of the particle drivers and traps in GIS. Finally, the effects of dielectric coating on the electrode and of gas pressure on the particle trajectory are also studied.     

GIS中的电磁暂态现象

GIS以其较高的运行可靠性,易维护,占地面积小等优点在电力系统中得到了广泛的应用。但是,在隔离开关、接地开关和断路器的动作过程中,会出现快速暂态过程。主要表现为:GIS母线套管上的快速暂态过电压和GIS壳体上的暂态地电位升高以及GIS周围空间产生暂态电磁场。主要分析和探讨由快速暂态过程引发的暂态电磁场的产生和传播机理以及它对GIS的电缆出线和与GIS相连的变压器的影响。     

Historical review of high voltage switchgear developments in the 20th century for power transmission and distribution system in Japan

In Japan during the 20th century, developments of high voltage transmission and distribution apparatus advanced tremendously and circuit breakers were the center of these developments. And as a result, 1100 kV SF/sub 6/ gas insulated switchgear (GIS) for ac transmission systems and also 500 kV dc GIS for dc transmission systems have become available. Vacuum circuit breakers (VCBs) have also been actively developed and a 168 kV two break VCB and 100 kA VCB are already available. This paper describes these developments and future trends in technology.