Compressed Gas Insulation Research Articles

Understanding surface charge accumulation and surface flashover on spacers in compressed gas insulation

Surface charges have the effect of changing the electric field over spacers in compressed gases, which may affect the stable operation of gas insulated equipment and could possibly trigger a catastrophic surface flashover without warning. In this paper, we review the literature on surface charge accumulation and related surface flashover phenomenon on spacers in compressed gases. A summary of experimental research of surface charge accumulation is presented and, the surface charge accumulation mechanism is also summarized, with some newly identified factors in mind that may affect surface charge transport and measurements thereof. Subsequently, the correlation between surface charge accumulation and the surface flashover phenomenon is thoroughly discussed, and the effect of surface charges on surface breakdown under applied voltage pulses of various waveforms is analyzed. Finally, several important research topics in this area are proposed. In addition, some ideas on potential surface charge control methods are presented to aid the design of a better spacer free from surface charges in future studies.

Movement Patterns of Metallic Particles in a Single Phase Compressed Gas Insulated Busduct with Electromagnetic Field Effect

Movement Patterns of Metallic Particles in a Single Phase Compressed Gas Insulated Busduct with Electromagnetic Field Effect

超高圧不燃変圧器の実用化

超高圧不燃変圧器の実用化

Electronic system for measuring non-destructively single electron emission rates from surfaces in compressed gases under high electric fields

Abstract The practical implementation of sampling the statistical variation in magnitude of prebreakdown avalanches is given which allows the high electric field electron emission from surfaces to be determined for the first time non-destructively. A six channel purpose-built compact pulse height analyser is described and special emphasis is placed on the design and evaluation of a low noise proportional amplifying system for the tiny electron and ion currents produced by the avalanches in the inter-electrode gap and their interaction with the input stage, so that the measurements can be made far removed from the destructive spark. Typical results are given which show that present data are vastly different from previous measurements by other workers employing a destructive method and that the deviation from Paschen's law in compressed gas insulation sets in when the electron emission rate becomes substantial (about 150 e/s(. Whilst present results are limited to 20 kV, it is intended to extend the voltage range up to 100 kV.

Spacer Involvement in Conducting-Particle-Initiated Breakdown in Compressed Gas Insulated Systems

This paper describes the results of an investigation into conducting particle initiated breakdown in a 76/250 mm coaxial electrode configuration, representative of a 145 kV gas insulated transmission line (GITL) or gas insulated substation. A free moving particle is known to initiate breakdown through a sequential two-stage process. The involvement of an epoxy disk spacer in such a breakdown, when the particle is at a distance from the spacer, is studied through specially designed experiments. For 6.4 mm long, 0.45 mm diameter aluminum particles it is observed that the discharge path may involve the spacer surface even when the particle is several centimeters away from the spacer surface. However, the 60 Hz ac breakdown voltages for discharge paths involving the spacer surface are not significantly different from those without spacer involvement, if the particle-to-spacer distance is greater than 3 mm.

Development of 1200-kV Compressed-Gas-Insulated Transmission and Substation Equipment in the United States

Major research and development (R&D) programs for the development of sulfur hexafluoride (SF6) compressed-gas-insulated (CGI) equipment for ultrahigh-voltage (UHV) application at 1100-1200 kV have been under way independently in both the United States and Japan. The CGI transmission and substation equipment under study and development in these countries has included the surge arrester, circuit breaker, CGI transmission bus, disconnect and ground switches, and an air-SF6 termination. The U.S. CGI program has also included development of a power transformer, shunt reactor, voltageand current-sensing instrumentation, and a line trap, all for 1200-kV application. This paper presents the overall status of development of CGI substation equipment for UHV application in the United States. It describes the major CGI components developed, highlights their key design aspects, indicates the present status of development and testing, and addresses the work remaining to establish final design concepts. The paper also includes 23 references, a number of which have not been widely distributed or included in any of the recently published bibliographies of UHV substation equipment.

Development of 1200-kV Compressed-Gas-Insulated Transmission and Substation Equipment in the United States

Major research and development (R&D) programs for the development of sulfur hexafluoride (SF6) compressed-gas-insulated (CGI) equipment for ultrahigh-voltage (UHV) application at 1100-1200 kV have been under way independently in both the United States and Japan. The CGI transmission and substation equipment under study and development in these countries has included the surge arrester, circuit breaker, CGI transmission bus, disconnect and ground switches, and an air-SF6 termination. The U.S. CGI program has also included development of a power transformer, shunt reactor, voltageand current-sensing instrumentation, and a line trap, all for 1200-kV application. This paper presents the overall status of development of CGI substation equipment for UHV application in the United States. It describes the major CGI components developed, highlights their key design aspects, indicates the present status of development and testing, and addresses the work remaining to establish final design concepts. The paper also includes 23 references, a number of which have not been widely distributed or included in any of the recently published bibliographies of UHV substation equipment.

New insulating materials and their use to achieve high operating stresses in electrostatic machines

Compressed gas insulation has provided the main insulation for sustaining terminal voltages of electrostatic accelerators. Essentially coaxial geometry is used with mechanical support of the terminal achieved by long columns which also support the acceleration tubes. Because of the vacuum insulation in the acceleration tubes, the electric gradient along the columns is typically 10–20 kV/cm, whereas the radial gas gap can operate at stresses about ten times larger. Until now, the terminal support has always been located in the low stress axial direction along the column and not in the radial high stress region. This paper is concerned with support insulation to be used in the radial direction. Advantages of radial supports include: simpler, more compact column structures, higher total voltages, and support of discrete stress redistribution electrodes such as vivitron. Important factors to the design of radial support insulators include the insulation constraints imposed by the gas gap, mechanical contact to the solid insulator, and basic limits of gas-solid dielectric interfaces. The gas gap insulation strength is shown to be limited by surface microirregularities and this accounts for electrode area and pressure effects. Based on the gas gap requirements, a design strategy for the insulators is developed. Epoxy is employed as the dielectric to allow the use of cast-in metal inserts at the ends. The inserts provide mechanical contact, shielding of the triple junction, and redistribution of the interface electric stresses. By careful design, the electric stress on the interface is made lower than that in the plain coaxial electrode gap. Practical experience shows that voltage increases linearly with insulator length and that designs achieve more than 10 MV/m into the multimegavolt region.

Electrical Design of the Revelstoke Hydroelectric Project

The Revelstoke hydroelectric project on the B.C. Hydro system is a six unit 2910 MV*A powerplant, with four units placed in service in 1984. The paper describes the basic design of the electrical features of the project including the main and station service single lines and the equipment parameters adopted. Special emphasis is placed on the power equipment aspects and the extensive use of 500 kV and 230 kV Compressed Gas Insulated (CGI) bus and switchgear. Some testing and early operating information is reported.

Breakdown mechanism and time development of discharges in compressed insulating gases

Compressed insulating gases with high specific electrical strength recently have become of increasing importance. Thereby compact insulating arrangements comparable with those using liquid or solid dielectrics can be constructed. For proper design those will have superior insulating characteristics. However great care must be taken to overcome interface problems which may occur at the electrode surface or at the surface of solid insulators. Compressed gas insulation can also be influenced even by short overvoltages. Therefore the voltage-time characteristic of compressed gas insulated apparatus is of special interest.

Gas Breakdown in Case of Steep-Fronted Pulses and Insulator Interfaces

Two fundamental factors influencing the insulating characteristics of compressed gases are steep-fronted overvoltages and interfaces between gas and solid insulators. In order to estimate the influence of steep-fronted overvoltages it is necessary to know the limiting voltage-time-characteristics, that is the formative time lag. Especially in electronegative gases it is necessary to separate the statistical time lag from the formative time lag as the first time interval may be many orders of magnitude higher than the second. It will be shown that especially in SF6 the formative time lag may be either extremely short or rather long, mainly influenced by the field distribution. In compressed gas insulation the breakdown voltage is reduced by even "clean" insulator surfaces. In this case breakdown is induced by one or several micro-discharges caused by local field enhancement at the insulator surface. Further electron multiplication must be caused by photoionization. Breakdown occurs if several micro-discharges develop and grow together.

Surface Flashover of Spacers in Compressed Gas Insulated Systems

The spacer surface in a compressed gas insulated apparatus constitutes the weakest electrical location in the system. Discharges originating at the spacer-gas-electrode interface and the electric field distortion at the spacer surface may cause surface flashover. The presence of water vapor, conducting particles, and other contaminants may alter the flashover characteristics of the spacer. This paper reviews the various types of spacers used in gas-filled systems. The flashover performance of spacers under contaminated conditions is also evaluated. Further areas of work on the flashover of spacers are proposed in order to obtain a better understanding of the mechanism of flashover and towards the design of an efficient and reliable compressed gas insulated system.

Free Conducting Particles in Compressed Gas Insulation

This paper presents an electrostatic study of free conducting particles that contaminate com pressed gas-insulated high voltage apparatus and transmission lines. Analytical and numerical techniques are used to describe the effect of the particle charge and the magnitude of the ambient electric field on the field intensification on and near the particle surface. The electrostatic force acting on filamentary and spherical particles as they lift off one electrode and move towards the other, is also analyzed. The techniques developed in this study enable the construction of a breakdown voltage profile which describes the instantaneous voltage required to break down the insulation as the particle moves between electrodes.

Particle-Initiated Breakdowns in Compressed Gas Insulation Under Time-Varying Voltages

The need is growing for an analytical model to describe the performance of particle-contaminated compressed gas insulation. The model should take into account the wide practical variety of particle shapes and sizes, insulation configurations, applied voltage magnitudes and wave forms, and gas pressure. This work introduces 'Breakdown Voltage Profile' as an attempt in that direction. The profile offers a description of the instantaneous breakdown voltage as a function of the location of a given particle within the gaseous insulation. The profile explains and, in turn, predicts such characteristics as critical particle position and free-particle and fixed-particle breakdown voltages. When properly combined with the particle moving trajectory under a transient (impulse) or steady state voltage, the profile enables the determination of the critical voltage magnitudes.

Particle-Initiated Breakdowns In Compressed Gas Insulation Under Time Varying Voltages

Particle-Initiated Breakdowns In Compressed Gas Insulation Under Time Varying Voltages

Time Dependence of Breakdwon Voltage and Endurance Testing of Compressed Gas Insulation

Factors which may influence the long term endurance characteristic of gas insulated equipment are discussed in this paper. Time dependence in the dielectric strength of gas is attributed to the statistical nature of the electrical breakdown in compressed gas. The influence of the factor will diminish in large scale practical systems. Solid insulators may be subjected to deterioration, but properly fabricated gas insulated equipment is normally designed to be free from those deteriorations.

Time Dependence of Breakdown Voltage and Endurance Testing of Compressed Gas Insulation

Time Dependence of Breakdown Voltage and Endurance Testing of Compressed Gas Insulation

Correction to "Particle-Initiated Breakdown in Compressed Gas Insulation Under Time-Varying Voltages

Correction to "Particle-Initiated Breakdown in Compressed Gas Insulation Under Time-Varying Voltages

Specification and Application of SF6 Compressed Gas Insulated Switchgear A Utility's Point of View

The introduction and application of a new technology, SF6 compressed gas insulated (CGI) switchgear has resuled in some problems not foreseen by the users nor are they adequately provided for in the existing standards for conventional switchgear. This paper discusses the accumulated experience of the B.C. Hydro and Power Authority in the areas of planning, specifications, tender evaluation, testing and operation of 550 kV and 230 kV minisubstations. Particular emphasis is placed on the need for national and international standards specially framed for CGI switchgear and for in-depth knowledge by present and potential users of this equipment.

A Test for the Effect of High Energy Arcs on the Flash-over Strength of Insulators in Compressed SF6

A test method for evaluation of solid insulating material for insulators in Compressed Gas Insulated Transmission (CGIT) systems has been developed. The test measures the ability of an insulating surface to withstand voltage after being subjected to a high energy power arc across its surface. The test has been used to evaluate several different solid insulators in SF6 at 0.4 MPa. The test circuit is designed to effect an efficient transfer of energy from a capacitor bank to an arc on the insulator surface. Voltage reversals in the capacitor bank are minimized. Flash-over of the insulator is initiated using an impulse generator. After exposing the insulator to the arc, the power frequency flash-over voltage is used as a relative measure of the ability of the material to withstand power arcs. The test circuit, sample geometry and representative measurements are described. Epoxy systems with the best performance in these tests showed little or no decrease in power-frequency flash-over voltage after arcing, while large reducitons were observed in other epoxies after only a few power arc-overs. This arc damage test was developed as part of an ERDA Contract to develop a prototype 1200 kV CGIT system.