Junping Zhao

The Breakdown Characteristics of Single-Gap Pseudospark Discharge Under Nanosecond Pulsed Voltages

In this paper, an experimental investigation of pseudospark discharge behaviors was conducted under nanosecond pulsed voltages using a flexible discharge chamber. The breakdown voltages of the pseudospark discharge gap were measured for a wide range of gas pressures, anode-cathode gap distances, and cathode aperture diameters to find the match of gap distance and cathode aperture diameter at a certain gas pressure with the nanosecond pulsed voltage. According to the experimental results, an empirical relationship was obtained. The roles of the parameters in the empirical relationship during the discharge were analyzed. The breakdown characteristics were also consistent with the Paschens law in the pseudospark under nanosecond pulsed voltages, when the gap distance was replaced by the effective gap distance. In the end, a possible reason was put forward to explain the difference between the empirical relationships obtained under dc voltages and nanosecond pulsed voltages.

3-MV compact very fast transient overvoltage generator for testing ultra-high-voltage gas-insulated switchgear

Gas-insulated switchgear (GIS) is widely used today in electrical power systems because of its reliability, compaction, long maintenance cycle, and small impact on the environment [1]. In its use the normal operation of the disconnector generates very fast transient overvoltages (VFTO) with frequencies ranging from 1 to 100 MHz [2] and amplitudes up to 2.5 p.u. [3]. For systems above 330 kV, the insulation strength of the GIS under VFTO is of concern as insulation failures caused by VFTO have exceeded those caused by lightning impulse (LI) [4]. This characteristic has attracted the attention of researchers worldwide and currently is a hot topic in the field of ultra-high-voltage (UHV) GIS insulation.

The Breakdown Characteristics of Multigap Pseudospark Under Nanosecond Pulsed Voltages

In this paper, breakdown characteristics of multigap pseudospark under nanosecond pulsed voltages were studied. Experimental results reveal that the characteristics under nanosecond pulsed voltages show the trend that the breakdown voltages decrease with the increase of the pressure and gap distance, increase with the increase of the number of gaps. Based on the experimental results, an empirical relationship was obtained. In the end, fast electron ionization effect has been observed, which offers successful explanations of the progress of multigap pseudospark discharge under nanosecond pulsed voltages.

Study on Characteristics of Nanopowders Synthesized by Nanosecond Electrical Explosion of Thin Aluminum Wire in the Argon Gas

As a new gas-phase synthesis method for the production of nanosize powders, the wire electrical explosion method has the advantages of high energy efficiency and high product purity through production under pure inert gas conditions and has been applied to the continuous industrial production of nanopowders. In this paper, an experimental device based on the electrical explosion of metallic wires for nanopowder production and collection is designed and built. Also, aluminum nanopowders were produced by electrically exploding an aluminum wire and collected by the microporous membrane filter successfully under different pressures of argon gas. Moreover, the influence of the argon gas pressure on the characteristics of the aluminum nanopowders was analyzed by a transmission electron microscope. The results showed that the particle shape, size, and distribution of the aluminum nanopowders could be controlled by the pressure of argon gas. The aluminum nanoparticles produced in the high-pressure argon gas had better spherical particle shape; meanwhile, the count mean diameter of the aluminum nanopowders increased obviously with the rise of the argon gas pressure. A higher pressure of argon gas could broaden the range of the aluminum nanoparticle size distribution evidently.

Effect of Medium on Deposited Energy in Microsecond Electrical Explosion of Wires

The properties of the medium have an obvious effect on the process of the electrical explosion of the wire. In this paper, the electrical explosions of copper and aluminum wires were investigated in air and water with pulsed voltage in a time scale of a few microseconds. Based on the measurements of the current and voltage waveforms in wire explosion with a self-integrating Rogowski coil and a voltage divider, respectively, the deposited energy in the stages of melting, liquid state, and vaporization was calculated by mathematical method. The effect of air and water on deposited energy in the three stages previously mentioned was analyzed by experiments and calculation. The results show that the pressure of the medium around the wire generated by compression from wire material expansion is an important factor of the effect of the medium on the energy deposition and the time of duration in the different stages. Additionally, the species of the medium also has an important effect on the formation of plasma discharge channel. The deposited energy in the electrical explosion of copper and aluminum wire in water is more than that in air, particularly after the beginning of vaporization.

Plasma Characteristics of Single Aluminum Wire Electrically Exploded in High Vacuum

In this paper, the plasma generated by the electrical explosion of a single aluminum wire in high vacuum is investigated, through self-emission spectrum in the range of near UV to visible wavelength (347.5–477.6 nm) captured by imaging spectrometer with the duration of the spectrometer time frame of 3 ns. Electron temperature and density of the plasma are determined through the spectrum using Boltzmann Plot and Stark Broadening Effect of isolated lines of Al III. The results show that the electron temperature in the plasma is in the range of 3.7–8.6 eV and the electron density has the order of magnitude about

Study on the electron emission process of the pseudospark during the hollow cathode phase under nanosecond pulsed voltage

10^{18}~{\rm cm}^{-3}

Fast Electron Ionization Effect in Multigap Pseudospark Discharge Under Nanosecond Pulsed Voltages

. Population inversion of Al II is found according to the intensity of the isolated lines in the spectra.

Wormholes effect in flashover process of alumina filled epoxy resin surfaces in SF 6

Pseudospark discharge, discovered in 1979, has remarkable parameters that may make it useful in various applications. This paper explores the influence of the cathode aperture on the breakdown characteristics of pseudospark discharge. In addition, the discharge process in both the main gap and the cathode aperture has been researched by a high-speed framing camera. Results revealed that the influence of the structure of the hollow cathode on the breakdown voltage characteristics lies in the structure of the cathode aperture. Besides, the delay of the electron emission process has been calculated based on the explosive electron emission model. In the end, a possible reason for the great discharge current and high increase rate of the discharge current has been discussed.

Discharge Mode in Electrical Explosion of Aluminum Wire Under Various Argon Pressures

In this paper, research studies on the breakdown progresses of multigap pseudospark discharge under nanosecond pulsed voltages are reported. The experimental results show great differences from dc voltages. The discharge mechanism of the pseudospark under nanosecond pulsed voltages has been successfully explained by the fast electron ionization effect. In each gap, collision ionizations caused by the fast electron start step by step, and development progresses are almost the same and approximately simultaneous until the main gap breaks down.