High Current Arcing Research Articles

Simulation of Electric Arc Characteristics Based on MATLAB/Simulink

In high-voltage circuit breakers and high-speed railway Pantograph-OCS system, the plasma arc directly causes economic loss to the ablation of the equipment. It is important to study the electrical characteristics of the arc. Therefore, based on MATLAB/Simulink, several existing arc models are simulated to obtain the voltage and current waveforms of the arc and the volt-ampere characteristics. Through comparative analysis, the applicable conditions, advantages and disadvantages of several models are clarified, which provides a reference for the improvement of future arc models. The results show that the high-current arcing phase and the high-resistance and low-current phase of the arc are considered separately, and the simulation results are more accurate. The arc model time constant and the dissipated power are regarded as the functions of the arc conductance, and the simulation results can better reflect the dynamic changes of the arc conductance.

Migration of Composite Contact Materials Components at High Current Arcing

The paper presents a method for testing transport of composite contacts materials under electrical arc conditions at high currents and for polarized electrodes. Tests and the discussion of results were carried out for silver-metal, silver-metal oxide and silver-tungsten carbide contact materials. Additionally, tungsten electrode was used as the second contact which was either cathode or anode. Spectrometric analysis of arc erosion components transported onto the second electrode and into the surroundings was carried out.

Dielectric recovery characteristics of a high current arcing gap

Experimental measurements of the dielectric breakdown strength of an arcing gap after current zero were made to determine the effects of arc chamber venting on the reverse recovery voltage needed to break down a recovering gap. The recovery conditions applied closely matched those created in a molded case circuit breaker under power line fault conditions. Three different vent sizes were used to determine the effect of gas pressure on the recovery characteristics of the plasma with recovery time between 170 /spl mu/s to 280 /spl mu/s, and currents from 3 kA/sub p/ to 15 kA/sub p/. Larger venting, providing increased cooling of the plasma, resulted in increased breakdown strength over the full range of currents. Based on the approximation that the recovering plasma breakdown strength is inversely proportional to plasma thermal temperature, breakdown voltage values were fitted to an exponential model to obtain plasma time constants and the initial hold-off voltage. Comparing these results to curve fits of E/p values showed E/p was a more accurate representation of the data. It is proposed to use E/p values when there is significant post current-zero chamber pressure. These results could be used as a guide to predicting molded case breaker interruption performance, especially for small arc chambers and short gaps.

The behavior of vacuum arcs between spiral contacts with a fixed-polarity arc shield

A framing camera was used to study drawn vacuum arcs between spiral-type contacts. This contact design imposes a transverse (radially directed) magnetic field to drive the arc column along the edge of the gap. The fixed electrode was electrically connected to a cylindrical arc shield. With the fixed electrode and shield as cathode, the manner of ignition of cathode spots on the shield depended on the peak arc current I/sub p/. For I/sub p//spl gsim/25 kA, the arc entered an intense columnar mode, and cathode spots were produced on the shield when the arc column expanded radially outward from the gap for brief intervals during its running motion. For I/sub p/=12.6 kA to /spl sim/25 kA, cathode spots ignited on the shield when cathode spots moved over the adjacent edges of the fixed contact and large spikes occurred on the arc voltage. With the fixed electrode and shield as anode, there was less interaction of the arc column with the shield. In this polarity, there was no formation of an anodic arc root on the shield at least up to I/sub p//spl ap/38 kA, and a different mode of high-current arcing was observed.

Vacuum arc discharges preceding high electron field emission from carbon films

Field emission measurements on chemical vapor deposition diamond and laser ablated a-C films show an activation step after reaching a certain critical electric field. At this field a vacuum arc of some hundred ns duration initiates. While high current arcing leads to the evaporation of the spot surface melting, amorphization or cracking of the film is encountered for lower currents. In any case, much higher electron emission can be observed after this activation procedure due possibly to tip formation resulting in an electric field enhancement. By using a 1 GΩ resistance the discharge current can be limited nevertheless, an activation is observed.

Nanoscale/Multilayer Gradient Materials for Application in the Electromagnetic Gun Systems

AbstractAnalysis of fired rails from electromagnetic railguns indicates severe surface damage occurs due to high current arcing and tribological mismatch. We have explored the behavior of several nanoscale multilayered materials as possible routes to improve the thermomechanical properties of the rail and armature materials . Structures investigated include (i) Ti-Co alloy on Ta-Cu alloy on dlc (diamond-like carbon) on stainless steel; (ii) Ti-Co alloy on Ta-Cu alloy on dlc on Cu, (iii) Ti-Co alloy on Ta-Cu on Cu; and (iv) Ti-Co on Ta-Cu alloy on Al. The alloys were all 50:50 at% and film thicknesses were in the range 400-1000 Å. The films were formed using a repetitively pulsed vacuum arc plasma deposition method with substrate biasing- and IBAD-like techniques. The surfaces were characterized by scanning electron microscopy, transmission electron microscopy, Rutherford backscattering spectroscopy, optical microscopy, microhardness measurements, arc erosion resistance and scratch resistance tests. Preliminary results show improvement in the microhardness, arc erosion resistance and scratch resistance, most especially for the dlc-coated surfaces. This kind of multilayered approach to the fabrication of electromagnetic railgun and armature surfaces could be important for future advanced Electromagnetic EM Gun systems.

Separation of spiral contacts and the motion of vacuum arcs at high AC currents

A framing camera is used to photograph the vacuum arc between separating spiral-petal vacuum interrupter contacts. The rupture of the molten bridge between the contacts first leads to a high-pressure, transient arc column. This arc motion can become constricted for several milliseconds before it goes diffuse as the current decreases to zero. The current through the spiral contacts produces a magnetic field perpendicular to the arc column, which forces the arc to move outward and run along the periphery of the petals. Several vacuum arc modes occur during the half-cycle of high current arcing. Movies, gap-current curves, and arc voltage traces are used to study the development of the arc motion and how it is affected by the contact structure. This information is used to generate arc appearance diagrams in which the arc form and motion are correlated to instantaneous values of current and gap for a wide range of peak currents. Appearance diagrams are shown for two ranges of opening delay from current onset. >

Vacuum interrupter design based on arc magnetic field interaction for horseshoe electrode

Computational methods for evaluating the complex magnetic field structure in axial magnetic field type vacuum interrupters based on horseshoe electrode geometry are demonstrated. Arcing behavior can only be understood by incorporating an arcing model. An essentially low-current arcing model is capable of predicting the high-current arcing behavior and can be used to optimize the contact structure. >

Ablation-Stabilized Arcs in Nylon and Boric Acid Tubes

Using the isothermal ablation-stabilized arc model of Kovitya and Lowke [1], the high-current arcing behavior in tubes made from nylon or boric acid can be predicted from the tube length and radius. In the analyses of such arcs that occur in expulsion fuses and circuit breakers, the physical properties of the vapors formed from the ablated liner materials are required. Values of viscosity, thermal and electrical conductivities, density, specific heat, enthalpy, and sonic velocity for nylon and boric acid plasmas have been calculated for pressures of 1, 10, and 100 atm (1 atm = 101.3 kPa) over the temperature range from 5000-30 000 K.

The Vacuum Interrupter Contact

A survey of developments in electric contact design for vacuum interrupters is presented. The major emphasis is placed upon those characteristics of contact design that have led to practical vacuum interrupters. A brief description is given of the different modes of vacuum arc that have been observed and how these modes occur during one-half cycle of high current arcing. In the main body of the paper the design philosophy behind vacuum interrupter contact design is presented. It is shown that only two classes of contact have achieved practical utilization. The first of these design classes causes a magnetic field to be impressed at right angles to the arc current and hence, causes the arc to move rapidly over the contact face. The second design class impresses a magnetic field parallel to the arc current. This forces the arc into a diffuse mode with many widely separated cathode spots and a diffuse current collection at the anode even at very high currents. Each of these contact designs is discussed and their advantages and disadvantages are deline- ated.

Voltage Effects of Low and HIgh Current Arcing on Vacuum Interrupter Contacts

Experiments are described which indicate the effect upon pulse breakdown voltage of high current arcing between copper electrodes in vacuum. Our results indicate a moderate degradation of breakdown voltage occurs when the electrode surfaces have been arced at currents exceeding 5000 A peak. This change is probably associated with the melting and erosion of the contacts by the arc. The degradation at the arc anode and the arc cathode appear to be about equal for all currents up to 45 kA peak.

Effect of mechanical contact force on withstand voltage of copper-bismuth and CLR vacuum interrupters

The d.c. breakdown voltages of two commercial vacuum interrupters, having different electrode materials, is measured prior to and following axial compression of the contacts in a hydraulic press. In one switch, the contacts are fabricated of copper-bismuth alloy and the other of a propriety material known as CLR. It has been found that the compression of the contacts results in reducing the withstand direct voltage (deconditioning) of the open contacts in both interrupters. After a few compression cycles, the deconditioning effect diminishes and almost disappears for the Cu-Bi contacts. The CLR switch shows some tendency to cold welding of the contacts. However, the welds are easily broken and after a few compression cycles the deconditioning is smaller compared with, for example, the deconditioning due to high current arcing. The d.c. and a.c. breakdown voltages of vacuum gaps can be made to have almost the same values after spark conditioning of both electrodes with alternating voltage.

Effect of Arcing on the Microstructure and Morphology of Ag-CdO Contacts

The changes in the microstructure, the composition, and the morphology of internally oxidized Ag-CdO contacts after high current arcing were investigated. The contacts were always opened on the same half cycle (60 Hz ac); thus one electrode was always the cathode, the other always the anode. Qualitative spectra of the arc at its midpoint were also taken, The results indicate that during arcing, there is a much higher concentration of Cd vapor than of Ag vapor in the interelectrode region. It is also found that the erosion of the cathode is more severe, and that the metal in the interior of the cathode craters is depleted of CdO, while a layer of Ag-Cdo is built up in the anode craters.