Influence of an insulating spacer on the V-tcharacteristics of a coaxial gas-insulated cable. II. Tests on EHV buses

For pt.I see ibid., vol.3, no.1, p.16-25 (1988). The V- t characteristics of EHV buses were evaluated for two configurations with rated voltages of 550 and 800 kV. The bus dimensions were 6 m in length and 17.8/53.3 cm and 20.3-61 cm in diameter, respectively. They were each fitted with two tripod-type epoxy spacers. The results show a pronounced influence of the supporting spacers on the V-t characteristic, corresponding to a reduced withstand voltage and less dispersion in the measured breakdown voltages. A statistical method is presented for deriving the V- t characteristics of a gas-insulated system from those of the individual components     

Electrical breakdown of SF6 at small values of theproduct pd

The breakdown of SF₆ when static and impulse voltages are applied at small values (from 10^-4 bar-mm to 1 bar-mm) of the product pd was investigated. It was found that the prevailing breakdown mechanism up to 8×10^-3 bar-mm was the Townsend mechanism. Between 8×10^-3 and 5.5 bar-mm the Townsend and streamers mechanisms combined, whereas from 5.5 bar-mm on the streamers mechanism took over. The Paschen law was found to hold for the points lying to the right of the minimum when static voltage was applied, whereas edge-type breakdown occurred on the points lying to the left of the minimum. When impulse voltage was applied, the Paschen law was valid only for the points to the right of the 1 bar-mm point. The electrode material affected the static and impulse breakdowns through the values of its work function     

Particle-Initiated Breakdown Characteristics and Reliability Improvement in SF6 Gas Insulation

Particle-initiated breakdown characteristics in SF6 gas are investigated. Breakdown voltages are greatly influenced by particle diameter especially for AC voltages, and for very fine metallic wire particles are much higher than those for moderately thick ones. The breakdown stress of a gas gap is obtained as a function of particle length and can be estimated fairly well by assuming a corona stabilizing zone. For a spacer, the electric stress which is parallel to its surface dominates surface breakdowns and the relation between the stress and particle length is experimentally determined. In order to increase breakdown voltages, the effects of both the dielectric coating on a high-voltage electrode and spacer shape are examined. Finally, the effectiveness of the dielectric coating on a grounded electrode is demonstrated to prevent particle levitation.     

High field performance of thin-wall spacers in a vacuum gap

This paper reports the electrical conduction and breakdown characteristics of thin-wall ceramic spacers for a field emission display (FED). These spacers bridge two thin-film electrodes, which represent the FED cathode and the phosphor anode in a FED. Techniques to set up a high aspect-ratio thin-wall spacer without glue were developed. An extra-low light detection 3D-imaging system using an intensified CCD camera was developed which was able to identify the location of low-level light activity in the stressed vacuum-gap, indicative of imminent device failure. Thin wall spacers made of various ceramics were investigated extensively. The scanning electron microscopy (SEM) surface investigation showed that zirconia spacers exhibited a smoother surface morphology compared to all other materials studied; however, their breakdown voltages were rather low. The breakdown voltages of alumina spacers were severely limited by triple junction effects. At HV, breakdown at the edge of the thin-film electrode was observed. This edge breakdown can be used to explain the saturation of the breakdown voltage vs. vacuum gap spacing. The results of this work are highly encouraging in that an ~1000 μm tall spacer can support ~18 kV dc, at least 80% above the expected operational voltage of HV FED. The spacer breakdown voltage is expected to improve through surface treatment and elimination of the electrode edge-breakdown and triple junction effects     

Corona Inception and Breakdown in Nonuniform Field with Insulating Support in Air

Corona inception and breakdown was investigated in air for point-to-plane gaps with cylindrical spacers under 60-Hz ac voltages. The effect of a series gap, between the high-voltage point electrode and the spacer, on corona inception and breakdown voltages was also studied. For epoxy spacers the corona inception voltage decreased but the breakdown voltage increased, compared to an equivalent point-to-plane air gap without a spacer. The corona inception voltage characteristic was found to exhibit a maximum at a certain value of the series air gap. The results are interpreted in terms of recently reported observations of spacer surface charging in air and in other insulating gases and insulating barriers.     

A Z-transform model of transformers for the study ofelectromagnetic transients in power systems

A Z-transform model, which combines transformer frequency-dependent short-circuit impedances with gain functions, has been developed. It sets up a relationship between transient voltages and currents on both sides of a transformer winding pair. The model can be used to calculate impulse responses of the transformers with open-circuit secondary winding as well as those connected to other networks. It could be incorporated into EMT (electromagnetic transient) programs for calculating the EMTs in power systems in which the distributed characteristics of transformer windings are to be considered     

碳纤维复合芯导线与钢芯铝绞线的起晕特性对比试验

为研究碳纤维复合芯导线（ACCC）的起晕特性,基于小电晕笼电晕测量系统进行了ACCC-600/71单根导线和LGJ-630/45钢芯铝绞线单根导线起始电晕特性的对比试验。试验结果表明：在干净及人工涂污下,ACCC-600/71导线的起晕电压均要高出LGJ-630/45导线起晕电压,说明ACCC-600/71导线确实能够降低线路损耗,在节能、环保方面具有良好运行性能;表面污秽会降低导线表面粗糙度系数,从而大幅度降低起晕电压,且污秽物颗粒度越大影响程度越高。     

间隔棒对塔线体系脱冰跳跃的抑制研究

输电线路电力事故主要由导线微风振动、导线舞动和覆冰导线脱冰跳跃3种情况引起。其中覆冰导线脱冰跳跃使得导线跳跃较大的幅度,导致相间间距不足引发电气事故,且较大的导线跳跃易引发机械事故,在三相导线呈竖直排列的线路中,脱冰跳跃引发的危害尤为严重。针对三相导线呈竖直排列的输电线路,建立输电铁塔一线一相间间隔棒体系的三档有限元模型．当覆冰导线脱冰跳跃时,在不同的脱冰相组合下,研究相间间隔棒对塔顶位移的抑制规律,并对几种相间间隔棒布置方案进行研究。得出在档距的2／9、1／2、7／9处加装相间间隔棒是最优布置方案。     

线夹回转式导线阻尼间隔棒防舞机理与模态分析

线夹回转式导线阻尼间隔棒已经大量运用到超高压和特高压输电线路中,但该种间隔棒的防舞效果需要进一步研究.根据间隔棒的设计原理与参数,研究和验证间隔棒的防舞机理.线夹回转式导线阻尼间隔棒的部分线夹可转动,使得子导线可绕其自身轴转动,从而使覆冰导线截面形状均匀,起到了舞动抑制作用.利用ANSYS软件,建立了导线间隔棒体系的三维有限元模型;通过导线间隔棒体系的模态分析,得到导线阻尼间隔棒体系前6阶模态的固有频率和固有频率振型图.固有频率和振型图分析结果表明,线夹回转式导线阻尼间隔棒具有较好的防舞作用,在此基础上,提出线夹回转式导线阻尼间隔棒的工程应用建议.     

快速振荡电压下SF6气体间隙放电的光电检测

利用光电倍增管及分幅式变象管高速相对放电产生的光信号进行了检测。实验证明,光电检测是研究快速振荡冲击（FOI）作用下SF6气体放电过程的有效手段。由检测结果可看出,SF6气体间隙在FOI下的放电特征与标准雷电波（LI）下的放电特征是不同的,负极性FOI作用下的放电机理遵循茎先导机理。     

Feasibility study of compact high-Tcsuperconducting cables

A conceptual design of a compact high-T_c superconducting cable was developed by using the Bean model. The experiments suggested that the Bean model provides a rough evaluation of hysteresis loss in high-T_c superconducting wires, which is supposed to be the main component of AC loss. A compact high- T_c superconducting cable was designed using a method based on the Bean model so that it could be installed in existing cable ducts. The results indicated that a compact high-T_c superconducting cable system can increase the power transmission capacity without the need to construct new cable ducts or tunnels. It has also been found that the high-T_c superconducting cable system is acceptable with regard to such system aspects as stability and short-circuit capacity     

Corona and breakdown characteristics between sphere electrode with a protrusion and plane electrode under negative pulse voltage in N/sub 2/ gas

Corona and breakdown characteristics for a configuration of a sphere with a needle and a plane in N/sub 2/ gas are studied. The protrusion was used to simulate a metallic particle attached to a high voltage conductor surface in power apparatus. The corona and breakdown characteristics depend on the vertical distance between the needle tip and the bottom sphere. It was observed that the breakdown path changed from needle-to-plane to sphere-to-plane while increasing the vertical distance of the needle from the plane. Although corona was generated at the needle-tip at first and developed in the direction of the plane, both the needle-plane and the sphere-plane breakdown occurred at some short vertical distances. The sphere-plane breakdown in that distance was triggered by corona from the needle.     

Partial and complete electrical breakdown in simulated hightemperature superconducting coils

The partial breakdown (PBD) and complete breakdown (BD) phenomena in a composite insulation system of glass fiber reinforced plastic (GFRP) and liquid nitrogen are investigated to find the PBD and BD characteristics in high temperature superconducting (HTS) coils at quench. The electrode system used is made from a coaxial spiral coil-to-cylindrical electrode with an insulation barrier and spacers, and is immersed in liquid nitrogen. A heater is mounted inside the coil electrode to generate boiling which occurs on quenched superconducting coils. The experimental results show that (1) the polarity of PBD initiation under 60 Hz ac applied voltage depends on the width l_c of the cooling channel, (2) PBD appears through a gas bubble locked between the coil and concentric insulation barrier due to the electrical gradient and the spacer, (3) breakdown voltages are affected severely by the risetime of the applied voltage and the current amplitude associated with PBD, (4) two kinds of BD mechanisms are found depending on the shape of the spacer, length of cooling channel and heater power     

Voltage-time characteristics for steep-front impulse voltages ofparticle-contaminated spacers in SF6 gas-insulated switchgear

The voltage-time characteristics of spacer surfaces for steep-front impulse waves are investigated under a particle-contaminated condition in SF₆ gas. The characteristics are measured as a function of particle length, particle position, and space shapes. Flashover voltages monotonically increase in the submicrosecond region as time to flashover is shorter, and are a minimum in the 1 μs region. Applicability of the equal voltage-time area criterion for estimating the voltage-time characteristics is discussed and the estimation is clarified. Moreover, it is demonstrated that an optimized spacer with ribs greatly improves flashover voltages in the submicrosecond region as well as in the 1 μs and power frequency region     

Fundamental insulation characteristic of high-pressure CO/sub 2/ gas under actual equipment conditions

SF₆ gas has been widely used in electrical power equipment such as circuit breakers and transformers due to its superior insulation and interruption characteristics. However since 1997, SF₆ gas has been designated a greenhouse gas subject to emission restrictions at COP3 (The 3rd session of the Conference Of the Parties to the United Nations Framework Convention on Climate Change) so a new insulating gas is needed as a substitute for SF₆ gas. This research considers the use of high-pressure CO₂ gas as an insulator while stressing the environment aspects. Fundamental insulation data for the insulating gas acquired supposing gas insulated switchgears (GIS) consists of; (1) insulation breakdown characteristics under clean conditions and, (2) insulation breakdown characteristics with metallic particle contamination. The parameters in this case were assumed from an actual apparatus viewpoint, to be a high gas pressure up to 2.0 MPa, an electrode size capable of determining the surface area effect, the electrode surface roughness, and metallic particle length, etc. at the base electrode of the 72 kV GIS. As a result, experiments using these parameters revealed insulation characteristics for high-pressure CO₂ gas and that negative lightning impulse decided the insulation design, as well as the present SF₆ GIS. The need for taking measures to suppress PD under AC voltage and also the need for restricting metallic foreign particles around the central conductor and insulating spacer were recognized     

1 000 kV特高压输电线路换位塔

1 000 kV特高压交流输电线路与其他电压等级的输电线路一样,长距离输电也需要平衡各相电压、电流,进行导线换位。根据500 kV输电线路几种导线换位塔型的运行经验和1 000 kV特高压的电气距离,初步规划出直线换位塔、小构架耐张换位塔、自身式换位塔、门型换位塔和分立式换位塔,并进行了技术经济比较。     

Use of gas plasmas to increase breakdown strengths in polycarbonatefilm/foil capacitors

It is shown that the electrical breakdown voltages of polycarbonate film/metal foil capacitors can be increased. This can be achieved by briefly exposing the metal foil in these spirally wound film foil sections to a low-pressure, low-temperature gas plasma. Exposure of tin/lead foil to a 96% CF₄/4% O₂ gas plasma for four min, for example, produced >500% increase in breakdown voltage of sealed polycarbonate capacitors     

Dielectric strength coordination and generalized spacer design rules for HVAC/DC SF/sub 6/ gas insulated systems

The problems of HVAC/DC gas insulated systems (GIS) dielectric strength coordination and support spacers design criteria are discussed in this paper. The most important challenge is to protect the spacers against flashover and consequently exclude them from consideration when coordinating an insulation of GIS. Both experimental and numerical studies demonstrate that electric field formation mechanisms and insulation behavior at SF/sub 6//epoxy interface are substantially different for AC and DC voltage excitations. Nevertheless, in actual power systems, HVDC apparatus are frequently subjected to impulse and time-varying voltages, implying capacitive field grading, and vice versa, HVAC apparatus can actually be subjected to harmful pseudo-DC voltages occurring in certain operating modes. Therefore, the above-mentioned problem is considered in order to find generalized criteria which will provide a reliable spacer performance in both HVAC/DC gas insulated systems. To illustrate the specificity of SF/sub 6//epoxy insulation behavior at HVDC stress, static V-T characteristics for post-type spacer models were studied experimentally. Dielectric strength coordination requirements and constraints arising for AC/DC GIS conditions were discussed. Some design and technological alternatives directed to improve the DC spacer reliability were analyzed. Based on these results, generalized design criteria for AC/DC conical and post type spacers were formulated. For conventional range of GIS operating stress and insulation parameters, it has been shown that proposed design rules can be realizable with no additional enlargement of apparatus dimensions. Such an approach provides unification and interchangeability of support spacers in HVAC/DC SF/sub 6/ apparatus, which could be technologically worthwhile and economically beneficial for manufacturers and power utilities.     

Dielectric breakdown in high-ε films for ulsi DRAMs: III. Leakage current precursors and electrodes

Abstract

A somewhat qualitative review of leakage currents J(V,t) in perovskite oxides is presented. It is stressed that space-charge-limited currents (SCLCs) are not alternatives to ionic conduction, Schottky emission, Poole-Frenkel, or Fowler-Nordheim tunneling, but can occur whenever currents due to any of those mechanisms reach a certain threshold and are no longer limited by the details of the metal electrode-ferroelectric interface. Standard metal-semiconductor band models that exclude surface states fail qualitatively to account for the experimental dependences of leakage currents and breakdown voltages on electrode work function; the correct model is metal-n-p-n-metal, with surface donor-state trapping. A discussion of conduction properties in these materials is presented from an ionic conductor viewpoint.     

Transformer modelling for distribution system studies. II. Additionof models to YBUS and ZBUS

For pt.I see ibid., vol.7, no.2, p.567-74 (1992). A distribution transformer modeling procedure is discussed which represents the distribution transformer with a minimum of input data for network, load, and fault studies thereby allowing the transformer to be routinely included as part of the distribution network. How these transformer methods are used in the formation of Y_BUS and Z _BUS system models is described