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

Biographical Motivations of Pilgrims on the Camino de Santiago

The question of what leads people from a biographical perspective to go on pilgrimage has been a research object in the Department of Sociology at the FernUniversität in Hagen, Germany. This qualitative study examines the biographical constellations which have led to the decision to go on pilgrimage and therefore a typology of biographical motivations was developed. To achieve the aim of a typology, methods of qualitative research were used. The database consists of narrative interviews that were undertaken mostly with German pilgrims. The life stories of the pilgrims were analysed with Grounded Theory Methodology and made into a typology of five main types of pilgrims: balance pilgrim, crisis pilgrim, time-out pilgrim, transitional pilgrim, new start pilgrim

“This trip is very meaningful to me, so I want to remember it forever”: Pilgrim Tattoos in Santiago de Compostela

Pilgrim tattoos have come into fashion: in Santiago de Compostela, the destination of all Ways of St. James, tattoo studios are springing up and in social networks, corresponding photographs can be found more and more often. In this paper we present the results of a survey of pilgrims who have been tattooed after their pilgrimage (N=256). It turns out that certain symbols and body parts are particularly popular among pilgrim tattoos. The tattooing practice of pilgrims also depends strongly on age, nationality and previous tattoos. The central features of the pilgrimage itself, on the other hand, have only a weak influence on the tattooing practice. The increasing popularity of pilgrim tattoos can therefore be seen as a further sign of a general renaissance of tattoos (Rees, 2016). Nevertheless, pilgrim tattoos fulfill an identity-forming function and should be seen in the context of the high biographical relevance of late modern pilgrimages

Studies of Breakdowns in Liquid Nitrogen at Different Pressures Between Rogowski Electrodes

AbstractThe usage of superconducting machines in the power grid or other high energy application makes it necessary that the machine can withstand all electrical stresses which can occur during normal operation and at transient overload. To guarantee a sufficient insulation, it is essential to know the properties of the insulating material. For HTS applications liquid nitrogen is a possible cooling and insulation liquid. In this paper the influence of pressurized liquid nitrogen on the discharge voltage is observed. Therefore, a cryostat was used, that can be pressurized and the discharge voltages at 3 barabs and 5 barabs were investigated. The investigations were performed between Rogowski electrodes to guarantee a homogeneous electric field without discharges at the electrode edges. Experiments were done with gap distances up to 7mm. The liquid nitrogen was stressed with lightning surge voltage of both polarities and AC ramp with a rise of 2000V/

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

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