Modeling of graphite electrode failure in high power spark gaps

Abstract

The purpose of this research is to determine the mechanism for the abrupt failure of graphite electrodes in high power spark gaps. The occurrence of damage was initially linked to a high current rate of rise (di/dt) of the system, on the order of 10/sup 11/ A/s. Under these conditions, no electrode fracture occurred. Diagnostics and theoretical modeling are provided and testing is to continue. An indirect technique is used to measure the magnitude and duration of dynamic stress on graphite electrodes during switch operation. Different operating conditions (i.e. different currents, energies) are used to obtain relative measurements. A preliminary model of the impact force on the electrodes as a function of circuit parameters is presented, possibly with a model of the force interaction and propagation through the electrodes. The experimental results are compared with the model. The ultimate goal is to pinpoint the cause of electrode rupture and improve the performance by altering external circuit, mechanical mounting or electrode geometry.