Electrical contact activation: A phenomenoloigcal model

Abstract

A phenomenological model of contact activation is presented based on diffusion of trace gaseous pollutants. The chemistry of these gases when adsorbed on the contact surface is discussed. Contact operating rates, gaseous pollutant concentrations, and contact surface roughness are considered. Experiments are performed and discussed which involve the decomposition of inorganic halogenated compounds and hydrocarbon compounds, the chemical effects of these compounds when on palladium contacts with protection circuits, and the rate of operation of contacts. Experimentally, an attempt is made to simulate conditions as they are found in the field whenever possible. The results of these experiments show that both classes of compounds can activate and thereby cause contact erosion when they are present at the ppm level. It is further shown that a 1-Hz versus 10-Hz relay operating rate can increase average arc time by typically a factor of 10 when 1 ppm of selected gaseous impurities are present in the atmosphere around the contact. These results fit the model as presented, agree with data collected from the field, and are capable of explaining erosion rate differences between the field and various life tests.