Effect of operating rate on the arc duration of activated telephone relay contacts

A contact operating rate effect, or more correctly, a contact open-time effect, has been experimentally measured on palladium wire spring relay contacts breaking a 50-V 100-Ω nominally resistive load in an air-diethylphthalate (?5 ppm) environment. The steady-state average arc duration is almost constant at 100 μsec for open times greater than 1 sec, and is proportional to the square root of the open time for open times less than 1 sec. To test whether the observed critical open time of 1 sec could be the result of a slow drift of clustered organic ions to the contact surface, the ion drift velocity of the various positive and negative ions was measured. The slowest velocity (?60 cm/sec) was found to be a thousand times too fast to explain the open-time effect. However classical diffusion of the organics to the contact surface can explain the 1-sec open time. The functional dependence of the open-time effect has been predicted by a dynamic activation model; however, this model only considered organic adsorption on the contact metal surface rather than on the carbon particles, which is more likely. A new dynamic model of the over-all contact activation process is therefore developed for the activating organics being adsorbed on carbon together with a new form of carbon removal based upon the carbon particles being burned with the oxygen adsorbed on the carbon particles themselves. This model successfully predicts the form of the experimentally observed contact operating rate effect.