Particle emission from low-current break arcs at atmospheric pressure

The particle production from low-current (0.48-A short circuit) nominally resistive break arcs between palladium-gold contacts have been examined under ``clean'' and ``activated'' conditions. Particles produced in air and in dry nitrogen were measured using a condensation particle counter which detected particles of approximately 20-Å diameter and larger, with a sensitivity limit of 25 particles cm−3 of air corresponding to about 5000 total particles per break arc under our experimental conditions. The operation of the relay at 15 Hz produced large numbers of particles, the production of which was nonlinear with the repetition rate, and therefore the experiments were carried out at lower cycle rates (<5 Hz). Under these conditions it was observed that after an initial period of about 500 operations, short (<10 μsec) break arcs did not produce any detectable particles. Particles were detected for arcs of greater than 30-μsec duration with the number of particles increasing with the arc duration. Activation of relay contacts with consequent production of particles was found to take place in both filtered air and dry nitrogen showing that the activation process does not require the presence of oxygen or atmospheric particles.