Vacuum Arc Ion Flux From Vacuum Interrupter Contact Gap

Dielectric properties of vacuum interrupters are influenced by metal vapour deposition on the inner ceramic surfaces. Therefore these surfaces are partly protected by shield electrodes. The metal vapour originates from the vacuum arc in the contact gap during switching off process. Metal layer thickness on ceramics after switching operations were measured by Gramberg and the negative effect on dielectric performance was demonstrated. In this paper we address the principle transport process of metal vapour in vacuum interrupters. Duning and Beilis performed ion flux measurements from vacuum arcs. We regard experiments with 5 kA effective arc current. There seems to be experimental evidence that the final particle transport onto the ceramic surface within a shield gap can be explained by particle tracing. The measured deposited layer thickness is taken as quantity to validate vapour densities and transport processes in vacuum interrupters

A Computational Model for High Current Density Arc Plasmas

A computational model for high current density arc plasmas is developed. Under the assumption of thermodynamic equilibrium the arc plasma is described as a compressible laminar fluid based on the magnetohydrodynamic (MHD) equations and the transport and thermodynamic properties of air. The arc plasma is studied in time and space on macroscopic values such as the temperature and the pressure. The simulation results are discussed and future research work is identified addressing the scientific domain of high current density arc plasmas

Development of a Plasma Solver for Surge Protective Devices using Spark Gap Technology

In this article we present the development of a single-fluid plasma model using the open-source CFD-based modelling framework OpenFOAM for the simulation of surge protective devices. The model uses a pressure based flow solver and supports the use of common radiation models such as the P1 model. Empirical models for electrode sheaths can be used and coupling the simulation to external circuits is possible. Some initial results are presented and compared with high-speed camera recordings

Experimental Investigations on Electrical Plasma Conductivity in a Model Spark Gap for Surge Currents

In this experimental investigation the electrical conductivity of plasma is measured during surge current using potential probes. The measurements were carried out in a narrow gap arrangement based on spark gap technology. In order to investigate the electrical conductivity during surge this model is tested using 8/20 µs surge currents according to the IEC 62475. The measured behaviour of the electrical conductivity during surge and the uncertainty of these measurements are discusse

Estimation of Current Density Using High-Speed-Camera Recordings in a Model Spark Gap during Surge Currents

For experimental investigations of short time plasma in spark gaps, as used in surge protective devices, high-speed camera recordings are used frequently. The analysis of these recordings provides further details regarding the plasma state and distribution. These deduced details are used to assist research and development processes. To increase the benefit of high-speed camera recordings an empirical model is presented to improve the picture analysis. In this model the recorded radiation intensity is empirically related to the current density within a spark gap. Therefore a specially adapted model spark gap was developed and tested. In this model spark gap areas with homogenous current densities occur. These current densities are determined in the experimental setup through current measurements with separated electrodes. Additionally, the relative radiation intensity between the electrodes is identified using high-speed camera recordings. An empirical correlation between these two measurement values was found and is discussed. It confirmed that the determined correlation improve the mostly intuitive interpretation of high speed camera recordings in spark gaps

Investigating of the Recovery Behaviour of a Small Switching Gap after Current Interuption

The recovery behaviour of switching arcs in a small gap was investigated experimentally. Therefore a simple mechanical model switch without an arcing chamber was designed. For the investigation the current carring contacts are separated. After various arcing times, the current is interrupted by an electronic switch. At a fixed contact distance, the switching gap was tested with variable voltages to investigate the dielectric strength. Based on these results the recovery behaviour was studied using the Weibull distribution function

Influence of Varying Gaps Between TMF Contacts on Constricted High Current Vacuum Arcs

The behavior of high current arcs in vacuum circuit breaker (VCB) is interesting for research and industrial development purpose which lead to further products. To improve the interruption capability of VCB, two approaches to control the arc have been proven successful. Applying transversal magnetic fields (TMF) on the arc is use for industrial VCB in medium voltage ranges. For greater gap distances the behavior of the arc is less thoroughly investigated. In this paper, the appearance of metal vapor arcs drawn by common TMF contacts in a vacuum-test-interrupter is investigated. An adapted drive mechanism enables to interrupt a fixed current with varying gaps from 5 to 25 mm and a constant opening time. Breaking operations with a 50 Hz current are observed with a high speed camera. With increasing gap distance a changed arc appearance can be observed. The goals of this work are to be understood as a feasibility study for optical evaluation methods for vacuum arcs under TMF

Diffusional Relaxation in Random Sequential Deposition

The effect of diffusional relaxation on the random sequential deposition process is studied in the limit of fast deposition. Expression for the coverage as a function of time are analytically derived for both the short-time and long-time regimes. These results are tested and compared with numerical simulations.Comment: 9 pages + 2 figure

Analysis of Radiation Discretization for Modelling a Spark Gap for Surge Currents

In this paper we address a method for spectrally resolved radiation modelling in thermal plasmas encountered in surge protective devices based on spark gaps. Compared to most switching applications, power input and plasma pressure are much higher which leads to an optically thick plasma with line broadening and enhanced wall ablation. In this situation it is possible to capture the full effect of spectrally resolved radiation on plasma dynamics by performing line-by-line calculations with downsampled absorption spectra. We show that it is possible to achieve radiation convergence with 1000 lines. Approaches for a further reduction of calculation times using band-averaged models and $\kappa$-group models are discussed. The κ-group model is based upon a grouping of the absorption coefficients into subgroups with different ranges of κ before averaging. The spectral calculation results are compared to the approximative methods and significant differences for Rosseland means are observed

Optical Investigations on Plasma Temperature Estimation in a Model Spark Gap for Surge Currents

In this experimental investigation optical emission spectroscopy is used to characterize the radiation of the plasma in a spark gap during surge. Different approaches are used, compared and discussed in order to estimate plasma temperatures. The measurements were carried out in a narrow gap arrangement based on spark gap technology. This model is tested using 8/20 µs surge currents according to the IEC 62475 with amplitudes of 5 kA and 11 kA