M.P. Paisios, A.D. Polykrati, P.G. Halaris, C.G. Karagiannopoulos, and P.D. Bourkas (Greece)
DC Measurement on stationary contacts, temperaturecoefficient, film resistance, constriction resistance, crossingresistance
This paper presents results of experimental investigations of the potential and temperature difference across DC-contacts in practical applications without interruption of power (stationary contacts), such as decouplers, fuse-boxes etc, under a constant clamping spring force (capillarity force), having DC-current values as parameters. The above-mentioned contacts have achieved a stage of moderate degradation, after aging in real operating conditions. According to our measurements the voltage drop versus time decreases across the contacts, at the first phase of reoperation and under a constant DC-current value. This fact indicates, that the thermal coefficient becomes negative at high current densities. The negative temperature coefficient may be attributed to microstructures formed on the apparent contacting area, such as oxides and other chemical compounds, creating an interfacial layer, which seems to show semiconducting behaviour. Based on the experimental results, we have attempted to make a mathematical approximation to determine the thermal coefficient.
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