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The absence of current-zero points in the direct current (dc) waveform of high voltage dc (HVDC) circuit breakers makes the interruption process more severe than the case of conventional ac networks with sinusoidal currents. In this way, in the current HVDC networks, a parallel precharged capacitor is inserted to inject the reverse current into the interruption chamber of the vacuum circuit breaker and create the artificial current-zero points. In this paper, a novel method for reverse current injection has been proposed. In this method, two separate helical flux compression generators (HFCGs) have been applied to generate the reverse current and an intense axial magnetic field (AMF), respectively. Numerical simulation of high-current vacuum arc (VA) in the presence of very strong AMF has been presented. For this purpose, the magnetohydrodynamic equations describing the behavior of the VA are coupled to a simple circuit analysis and the previously developed multiphysics model of HFCG. The results indicate that the explosively driven current injection set can make current-zero points properly in a typical HVDC network and lead to successful interruption of fault current. This method needs much less volume and cost in comparison to the parallel precharged capacitor sets. Index Terms--DC power transmission, pulse power systems, vacuum arc (VA), vacuum circuit breakers, vacuum interrupters (VIs).

Flux compression generators (FCGs) are widely used to generate extremely high power pulses. When a peak current from a seed source is flowing through the generator circuit, the chemical energy of high explosives is used to increase the amplitude of the output current pulse applied to the load. During the transfer of explosive energy to the output electrical pulse, the critical issue is achieving a change in the inductance in a fast and controlled way. There have been many significant experiments on different kinds of FCGs, and almost all of the theoretical models used to describe generator behavior are based on empirical equations. In this paper, simultaneous detonic, electromagnetic, and circuit simulations are used to study the characteristics of helical FCGs. For this purpose, the magnetic field diffusion and losses due to the induced currents in metallic components are considered in more detail. Based on the results of these theoretical considerations, new modifications for the FCG are proposed. It will be shown that the proposed modified FCG geometries yield output current rise times that are about 60% of those achieved with conventional helical FCGs generating the same current pulse amplitudes. Index Terms--Explosive pulsed power, helical flux compression generator (FCG), magnetic field diffusion.

In some plasma applications, such as confinement and pinches, an ultrahigh magnetic field (several teslas) is required. Such magnetic flux densities can be produced by using flux compression generators (FCGs). This paper has proposed a joint thermodynamic and electromagnetic simulation method for a common type of FCGs (i.e., helical type) with respect to the magnetic coupled plasma studies. The images of displacements, pressure, and magnetic flux density distribution in generator and plasma chamber are presented as simulation results. Index Terms--Explosions, flux compression generators (FCGs), magnetic coupled plasmas, thermodynamic and electromagnetic simulation.

Subnanosecond breakdown of low-pressure gaseous spark gaps has been investigated by using a combined modeling of the volume discharge in gas and the electron emission at the electrodes. Simulation results predict minimum breakdown delays of about 400 ps for the geometries considered in this paper. These results are in good accordance with the measurements. Index Terms--Pulsed-power switches, subnanosecond breakdown, thermofield electron emission, volume discharge.