Roland Michal

Investigation on the Switching Behavior of AgSnO 2 Materials in Commercial Contactors

The switching behavior of several varieties of Ag/SnO 2 contact materials was tested in commercial contactors and the results are compared with those obtained with standard Ag/CdO material. The properties tested were arc erosion under AC3 and AC4 conditions, contact resistance, temperature rise under continuous current, and making capacity. It was found that the newer Ag/SnO 2 -type materials, which contain WO 3 or MoO 3 in order to reduce overtemperatures, qualify as substitutes for Ag/CdO.

On the application of W/Cu materials in the fields of power engineering and plasma technology

The application of tungsten/copper materials produced by powder metallurgy as contacts and electrode materials in power engineering and plasma technology is discussed. These materials are suitable for use as electrodes in spark gaps, CO/sub 2/ lasers, and excimer lasers. By means of varying microstructure and tungsten content, as well as by introducing suitable additives, it is possible to optimize the material for quite a number of specialized tasks. The ways to influence the switching properties or the discharge behavior, respectively, are demonstrated with the aid of experimental results obtained in various applications of copper-tungsten materials. Application examples include switchgear, circuit breakers, transformer tap changer, vacuum contactors, vacuum load switches, contactors in a protective atmosphere, and electrodes for gas lasers.<<ETX>>

Erosion Characteristics of Silver-Based Contact Materials In a DC Contactor

Electrical life tests in a dc contactor are performed under DC4 and DC5 conditions. Results from our observations and erosion measurements are compared for different silver-based contact materials. For the device used a relation can be established between the arc energy and material loss and transfer. The erosion mechanism during the make operation determines the overall arc erosion to a larger than expected extent. Silver nickel 90/10 stands out as the contact material with the lowest erosion rate under both conditions.

Optoelectronical Position Indicators Applied to Arc-Motion Research

Two optoelectronical position indicators yielding continuous information about the arc motion are presented. The application of a system consisting of one of these position indicators and a proper computer system yields information comparable with highspeed cinematography. However in contrast to film technique, the evaluation of one test is very inexpensive and requires only a small amount of time. These two optoelectronical position indicators are applied to arc-motion research, and the various stages of the arc motion influenced by a transverse magnetic blast field in an opening contact (e.g., arc immobility and initial arc motion, arc running, and arc-spot commutation) are discussed. The experiments show that these devices are especially qualified to be used in arc-motion re- search.

Metal-Filled Polymer Combining Electric Conductivity and Gas Blasting

Metal-filled polymer (MFP) electrodes are presented producing extensive interactions with the switching arc. These electrode materials have an electric conductivity of a few percent of a good electric conductor like copper. Under the thermal stress of an arc spot they evaporate hydrogen and other gases yielding a strong axial gas blast effect on the arc column. Thus arc voltage and arc extinguishing capacity during current zero interval are remarkably increased. Also additional fillers like polytetrafRuor0ethylene (PTFE) may favor the arc extinguishing properties. The current carrying capacity and the Switching performance of a typical metal-filled polymer is discussed using a simple electrode arrangement especially suited for this material.