Low-voltage arc quench is one of the most processes for a successful power interruption in circuit breakers. Typical circuit breakers are designed to switch off the fault current within half a cycle, less than 10 milliseconds, which requires an efficient arc quench and thus poses great challenges in power interruption. Apart from using power electronics, which is very expensive and of low capacity, the classical circuit breakers that uses a stack of steel plates to split the fault-current arc into many sub-arcs are still dominant for both industry and residential installations. Due to the high current, the self-induced magnetic field will drive the arc towards to the steel plates and force the arc being spitted into many sub-arcs, from which the arc-steel plate interfaces generates multiple voltage drops. Once the sum of all voltage drops increases and exceeds the source voltage, the arc will extinguish and quench. Due to the ferromagnetic effect, the magnetic field increases dramatically during arc splitting by steel plates. However, the self-induced magnetic field have reversed direction on both sides of the steel plates which pushes the sub-arcs to opposite directions and prevents concurrent and even arc splitting. In this report, we report a new technique to compensate the self-induced the magnetic field by using a background magnetic coil, thus, to give an even and simultaneous arc splitting and guarantee the power interruption.
Plasma interacting with electrodes is one of the most challenging issues in many industrial applications, such as power-interruption and plasma-metal erosion. Because of the concentration of arc attachments (root) and the voltage drop across the plasma sheath layer, the arc roots consume great amount of energy, which subsequently will increase the local temperature and erode the electrodes. Due to the nonequilibrium condition at plasma sheath, it is very difficult to quantitatively estimate the arc root temperature profile. The recognition of arc roots behavior, like instability and pattern formation, is important to estimate the electrode erosion. The potential drop arising through the sheath (double layer) is nonuniform. Due to thermionic field emission, the strong flux of charge carriers through the sheath will cause instability of the double layer, which weakens the inner potential gradient. As a result, the strong current dependent potential drop features a negative resistance. The existence of negative resistance causes the instability of arc attachments in the forms of immobility and constriction. Their interdependence between local current density and potential drop gives rise to the arc root formation that concentrates the energy into a small spot. Owing to the negative resistance, any perturbation will cause the current density in the sheath to grow to approximately infinity or decay to vanish, namely arc root formation or extinction. Thereby, the arc root instability provides the basis for the dynamic behavior of arc attachments and detachments on the electrodes, which will help to understand electrode erosion and avoid the damage from the arc plasma in engineering applications.
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