Spatial and time characteristics of short gap, highdi/dt discharges

Under certain network conditions, vacuum circuit breakers may generate high-frequency currents. The quenching capability of vacuum circuit breakers for line-frequency currents and high-frequency currents plays an important role in the generation of unwanted voltage transients. This may occur when the gap distance at current zero is still too short to withstand the external voltage to the switch (TRV). The results of simulation calculations regarding these phenomena in the vicinity of current zero are described. Simulations are based on a detailed physical model, taking into consideration the basic conservation laws, the Maxwell equations, and the current continuity. The numerical solution takes into account the results of experimental streak photographs, revealing that the visible discharge covers only a small part of the contact diameter     

Some interruption criteria for short high-frequency vacuum arcs

If the contacts of a vacuum interrupter open shortly before a current zero, the transient recovery voltage (TRV) can cause a reignition and reestablish the arc. When the current in a diffuse vacuum arc passes through zero, there is a distinct pause before the TRV builds up (approximately 40 ns for copper). During this pause the gap carries conduction current only with an ion component which depends on dI /dt, varying between 3 A for dI/dt=60 A/μs and 60 A for dI/dt=1235 A/μs. The ion current subsequently decays in tens or hundreds of nanoseconds. It can be distinguished from the displacement current at this time by varying dV/dt, keeping the other parameters constant. Among the interruption criteria for short high-frequency vacuum arcs, dI /dt prior to current zero and initial dV/dt are the most important. High values of dI/dt are more likely to precipitate reignitions, but breakdowns can occur after lower dI/dt's if the gap has been subjected to a high current for a relatively long time (>100 μs)     

Computer simulation of post-arc plasma behavior at short contactseparation in vacuum

Rapid commutation of a vacuum arc prior to zero results in the postarc current that subsequently flows due to the transient recovery voltage (TRV) developing across the interelectrode gap. If the rate of change of the arc current exceeds the ability of the device to interrupt the condition, it can be reestablished in the reverse direction, i.e. what was the anode becomes the new cathode. An attempt to model the postcurrent zero phenomena in the light of gas dynamics as applied to the plasma of the metal vapor arc is described. The basic conservation laws and the Maxwell equations, as well as the current continuity law, are formulated and the solutions of those equations are presented. The short distance between the electrodes in practice of much less than a millimeter is specifically noted