SF6 Spark Research Articles

Mechanism of Trace O2 on SF6 Characteristic Decomposed Components Under Spark Discharge

Trace O2 significantly affects the diagnosis accuracy of decomposed components analysis method for spark discharge due to its direct participation in SF6 decomposition process. Therefore, spark discharge decomposition experiments were conducted under different proportions of SF6/O2 mixtures. The influence rules and mechanisms of φ(O2) on the content and characteristic ratio of SF6 spark discharge decomposed components were analysed quantitatively. Meanwhile, the materials on the electrode surface after spark discharge were conducted XPS analysis. Results show: no matter how much O2 adds, there exist SOF2, SOF4, SO2, and SO2F2 in the process of SF6 decomposition. The increase of φ(O2) plays a positive role in the production of SOF4 and SO2F2, but has the adverse effect on SO2. The content of SOF2 barely changes with φ(O2) increasing. Characteristic ratio φ(SO2F2 + SOF4)/φ(SOF2) gradually grows with φ(O2), but change little with discharge time extended. The X-ray photoelectron spectra show that the solid materials on the surface of the plate electrode after discharge contain Al2O3 and AlF3, and S mainly exists as metal sulfides.

Study on the influence rules of trace H2O on SF6 spark discharge decomposition characteristic components

To figure out the influence rules of trace H2O on SF6 decomposition characteristic components under spark discharge, a series of spark discharge decomposition experiments with various H2O contents were performed using needle-plate electrode to simulate metal protrusion insulation defect. The changing rules and mechanisms of five decomposition characteristic components were achieved quantitatively, indicating that no matter how much H2O was, there exist five main decomposition components: CF4, SOF2, SO2, SOF4 and SO2F2. The contents of the five decomposition components increased with the time extended, and resulting in the contents of SF6 spark decomposition components by the order: SOF2 > SO2F2 > SOF4 > SO2 > CF4. Additionally, the higher H2O content is, the stronger promoting effect on the generation of SO2F2, SOF2, SOF4 and SO2 is.

Investigation on SF6 spark decomposition characteristics under different pressures

The decomposition characteristics of SF6 gas-insulated equipment remarkably vary under different working pressures (0.3–0.7 MPa). Thus, the influence of pressure should be considered when adopting decomposed components for spark discharge fault diagnosis. A series of experiments on SF6 spark discharge decomposition under various pressures were performed on the spark discharge simulation experimental platform. The influence of pressure on SF6 spark discharge decomposed components were analyzed quantitatively combined with molecule chemical decomposition mechanisms. Results show that the species of spark decomposed components do not vary under different pressures. However, pressure directly affects the accumulated energy of the electrons in the spark channel, leading to diverse dissociation intensities of electrons on SF6. This phenomenon further affects the rate of neutral-neutral molecule and ion-molecule reactions responsible for the decomposed components. Finally, the yields and effective generation rates of decomposed components CF4, SOF4, SO2F2, SOF2, and SO2 decline with varying degrees under increasing pressure. Moreover, mathematic regression equations were derived for the effective generation rates of the components influenced by pressure.

Influence Mechanisms of Trace H2O on the Generating Process of SF6 Spark Discharge Decomposition Components

Trace H2O directly participates in the SF6 decomposition generating process under spark discharge, but its mechanism remains ambiguous. Thus , determining the influence rules of trace H2O on the decomposition characteristics of SF6 spark discharge is necessary . Moreover, the foundation of the effective spark discharge fault diagnosis methods should be established for SF6 gas-insulated apparatus. In this paper, a series of spark decomposition experiments of different proportions of SF6/H2O mixtures were conducted with a trace H2O injector accurately controlling H2O content. Influence mechanisms of trace H2O on the effective generation rates and the characteristic ratio of spark decomposition components were determined. Results show that trace H2O remarkably influences the effective generation rates of SF6 spark decomposition components, including SOF2, SOF4, SO2F2, SO2 and CF4. The characteristic ratio varies because of the distinct mechanisms of H2O on the components. Mathematical expression between the ratio and H2O contents was also derived. In addition, the X-ray photoelectron spectra show that the solid materials contain Al2O3 and AlF3, and the existing forms of S are sulfite and sulfate.

Pulsed energy storage antennas for ionospheric modification

Abstract. Interesting, "new", very high peak-power pulsed radio frequency (RF) antennas have been assembled at the HIPAS Observatory (Alaska, USA) and also at the University of California at Los Angeles (UCLA, USA); namely, a pair of quarter wavelength (λ/4) long cylindrical conductors separated by a high voltage spark gap. Such a combination can radiate multi-megawatt RF pulses whenever the spark gap fires. The antenna at HIPAS is 53m long (λ/2) with a central pressurized SF6 spark gap. It is mounted 5 meters (λ/21) above a ground plane. It radiates at 2.85MHz. The two antenna halves are charged to ± high voltages by a Tesla coil. Spark gap voltages of 0.4 MV (at the instant of spark gap closure) give peak RF currents of ~1200A which correspond to ~14 MW peak total radiated power, or ~56 MW of Effective Radiated Power (ERP). The RF pulse train is initially square, decaying exponentially in time with Qs of ~50. Two similar but smaller 80-MHz antennas were assembled at UCLA to demonstrate their synchronization with a pulsed laser which fired the spark gaps in the two antennas simultanoeously. These experiments show that one can anticipate a pulsed array of laser synchronized antennas having a coherent Effective Radiated Power (ERP)>10GW. One can even reconsider a pulse array radiating at 1.43MHz which corresponds to the electron gyrofrequency in the Earth's magnetic field at ~200km altitude. These "new" pulsed high power antennas are hauntingly similar to the ones used originally by Hertz (1857-1894) during his (1886-1889) seminal verifications of Maxwell's (1864) theory of electrodynamics.

A 10-GW Pulsed Power Supply for HPM Sources

A research activity involving the detailed consideration of novel high voltage transformers (HVTs) for pulsed-power applications has recently begun at Loughborough University (LU). Although the main goal is the demonstration of a compact and lightweight unit employing magnetic self insulation under vacuum conditions, the initial stage of the work is directed towards the development of a conventional air-cored HVT as a main component in a compact power supply for HPM sources. In cooperation with the Swedish Defence Research Agency (FOI), the power supply has been tested with a HPM source of the vircator type. The power source for the system uses a 70 kJ/25 kV capacitor bank and an exploding wire array to generate a 150 kV voltage pulse in the primary circuit of the HVT. A pressurised SF6 spark gap in the secondary circuit sharpens the high-voltage output, so that pulses approaching 500 kV and with a rise time below 100 ns are generated on a 20 Omega high-power resistor. The peak power produced by the power supply is in excess of 10 GW. Measurements provided by various diagnostic techniques are analysed with the aid of a detailed numerical code. Experimental results are presented from final testing of the system, where a reflex triode vircator replaces the 20 Omega resistor. Measurements made of the microwave emission using free-field sensors are presented for various electrode configurations. Comments are made with the microwave emission from the same vircator powered by a Marx generator at FOI.

Delayed expansions and ionization instabilities observed in the current decay phase of a SF6 spark discharge

In SF6 gas at 5–30 Torr, self-breakdown spark discharges starting in a constricted phase expanded spatially when the discharge current decayed to a critical value. The strength of the electric field increased from 400 to 2×103 Td in E/N, where 1 Td=10−21 V m2, where E is the electric field and N is the neutral gas number density. At the same time, the optical emission from the spark increased in strength and ionization instabilities started to grow. In the decay phase of SF6 spark discharge, negative ions strongly enhanced electron diffusion in the multipolar diffusion that resulted in the expansion and the excitation of ionization instabilities.

Pulse power technologies and related new approaches in LIMAY-I.

Technological troubles and new approaches in a pulse-power machine : LIMAYI as a relativistic electron and light ion beam generator are reported. Liquid Fron-113 is successfully tested as insulator of the Marx generator for the first case. We develop a new type of a SF6 spark gap switch for the Marx generator.

The transition between two glow discharge phases in the SF6 spark

The glow phases of sparks in SF6 have been studied at pressures around 1 Torr, and for discharge gaps of between a few cm and 1 m. Applied voltage pulses were maintained low enough so that the sparks did not proceed to their final arc phase. Measurements were made of discharge current, voltage and axial potential distribution as functions of time, and information on neutral particle density as a function of time was obtained using a polarization interferometer. The SF6 spark was found to develop through two glow phases. The first is a low current (tens of mA) phase, in which little molecular dissociation occurs; it is dominated by electron attachment. Gas heating during this phase leads to dissociation in times of the order of 100 mu s, and a transition occurs to a higher current (around 1 A) glow phase. In this dissociated phase, electron attachment is not so important. The interferometer study showed the increase in discharge refractivity due to dissociation, which accompanies the glow-glow transition. Further evidence for the role of dissociation in the transition was obtained from comparison of the SF6 spark with sparks in hydrogen, argon and SF6/argon mixtures.

KrF Laser-Triggered SF6 Spark Gap for Low Jitter Timing

KrF laser-triggered spark gaps exploit the high dc-dielectric strength and low ultraviolet (UV) breakdown threshold of SF6 gas. Detailed measurements using a dc-charged pulser demonstrate subnanosecond jitter for switching a 0.5-cm gap operated at 80 kV with 7 mJ in 20 ns of 248-nm KrF radiation. A 200-kV pulse-charged 0.7-cm gap gives similar performance.

Line Entrance Protection of 500 KV Gas Insulated Substations by SF6 Spark Gaps

The use of both station arresters and line entrance arresters provides absolute protection for all operating conditions of gas insulated substations (GIS). However, it represents a costly installation. Hence the adoption of line entrance rod gaps in air can be taken into consideration. But their protection ability is questionable because the slope of the V-t curves for air gaps is much steeper than that for GIS, while SF6 spark gaps with good sparkover characteristics would meet the requirements for the ability to protect the line entrance apparatus of GIS.

The Hydra Electron Beam Generator

The Hydra electron beam generator was designed to simrultaneously produce two 1 MV, 0.5 MA, 80 nanosecond electron beams that could be combined to form a single beam. The machine, undergoing final developmental tests, has generated a 0.5 MA, 1 MV peak electron beam from each line. This accelerator consists of a low-inductance Marx generator, two water-dielectric pulse-forming (PF) and impedance-transforming transmission lines and two low-inductance, high-current diodes. A description of the generator is presented along with developmental studies and initial testing data. The Hydra machine is based on accelerator principles described in the literature. The Marx generator is submerged in transformer oil and separated from the transmission line water by a lucite interface. The Marx charges each coaxial PF transmission line which is deionized water insulated to 3 MV in 0.9 microseconds. At peak voltage, a 3 MV SF6 spark gap electrically connects the 4 ohm PF line to the impedance transforming (4 ohm to 2 ohm) transmission line. The pulse is transmitted through this line to the single radial insulator diode. A 30 kilojoule, 100 nanosecond duration electron beam is formed by a cold cathode in each diode.