| The behavior of rapidly commutated (up to 1.2 kA/(mu)s) diffuse vacuum arcs has been studied using three different interrupters: (a) A GE 10 cm diameter Cu electrode interrupter, (b) a GE 10 cm diameter Be electrode interrupter, and (c) a VIL (V5) interrupter.; These interrupters were tested using a synthetic test circuit which allowed independent variation of arc current prior to commutation (I(,ss)), the dI/dt at current zero and the dV/dt following current zero. Post arc currents and voltages were recorded. Whereas the peak post arc current (I(,pk)) was found to vary with I(,ss) at higher dI/dt, V(,pk) is a function of dI/dt only. Only two breakdowns occurred for the VIL and GE Be interrupters whereas the occurrence of breakdowns for the GE Cu interrupter increased rapidly above 400 A/(mu)s.; A theoretical model for sheath growth, including the influence of variations in current during the ion flight time has been developed. The model can be used to: (a) derive plasma parameters from test oscillograms; (b) given the plasma and circuit parameters, predict the post arc behavior of the interrupter.; The model predictions agree well with experimental results. Higher ion charge to mass ratio, electrode area or commutating inductance reduce electric fields at ex-Anode and the probability of breakdown. Higher plasma charge density and dI/dt increase the probability of breakdown. Breakdown fields in the presence of plasma are found to be higher than in its absence and could be due to in situ electrode conditioning. |
