Study on the formation of arc plasma on the resistive wall liquid metal current limiter

Due to its significant attributes,the liquid metal current limiter(LMCL)is considered a new strategy for limiting short-circuit current in the power grid.A resistive wall liquid metal current limiter(RWLMCL)is designed to advance the starting current-limiting time.Experiments are performed to investigate the dynamic behaviors of liquid metal,and the influence of different currents on the liquid metal self-shrinkage effect is compared and analyzed.Furthermore,the liquid metal self-shrinkage effect is mathematically modeled,and the reason for the formation of arc plasma is obtained by simulation.The laws of arc plasma formation and the current transfer in the cavity are revealed,and the motion mechanisms are explained by physical principles.The simulations are in accordance with the test data.It is demonstrated that the sudden change of the current density at both ends of the wall causes the liquid metal to shrink and depress under the electromagnetic force,and the current starts to transfer from the liquid metal path to the wall resistance path.The RWLMCL can effectively advance the starting current-limiting time.

A novel fault current limiter topology design based on liquid metal current limiter

The liquid metal current limiter(LMCL)is regarded as a viable solution for reducing the fault current in a power grid.But demonstrating the liquid metal arc plasma self-pinching process of the resistive wall,and reducing the erosion of the LMCL are challenging,not only theoretically,but also practically.In this work,a novel LMCL is designed with a resistive wall that can be connected to the current-limiting circuit inside the cavity.Specifically,a novel fault current limiter(FCL)topology is put forward where the novel LMCL is combined with a fast switch and current-limiting reactor.Further,the liquid metal self-pinch effect is modeled mathematically in three dimensions,and the gas-liquid two-phase dynamic diagrams under different short-circuit currents are obtained by simulation.The simulation results indicate that with the increase of current,the time for the liquid metal-free surface to begin depressing is reduced,and the position of the depression also changes.Different kinds of bubbles formed by the depressions gradually extend,squeeze,and break.With the increase of current,the liquid metal takes less time to break,but breaks still occur at the edge of the channel,forming arc plasma.Finally,relevant experiments are conducted for the novel FCL topology.The arcing process and current transfer process are analyzed in particular.Comparisons of the peak arc voltage,arcing time,current limiting efficiency,and electrode erosion are presented.The results demonstrate that the arc voltage of the novel FCL topology is reduced by more than 4.5times and the arcing time is reduced by more than 12%.The erosions of the liquid metal and electrodes are reduced.Moreover,the current limiting efficiency of the novel FCL topology is improved by 1%–5%.This work lays a foundation for the topology and optimal design of the LMCL.

Closing performances of double-gap laser-triggered vacuum switch

To develop high-voltage-pulsed power switches with better performances,a multi-gap laser-triggered vacuum switch is proposed in this study.Based on established test pro-totype for double-gap laser-triggered vacuum switch,closing processes of double-gap laser-triggered vacuum switch are discussed combined with laser-produced plasma.Closing performances of double-gap laser-triggered vacuum switch under different gap polarity configurations,operating voltages,laser energies and laser split ratios are inves-tigated.Closing time delay characteristics of double-gap laser-triggered vacuum switch and single-gap laser-triggered vacuum switch are compared later.The test results prove that,affected by the imbalanced developed initial plasma between gaps,double-gap laser-triggered vacuum switch with two positive gaps and 1:1 laser split ratio presents best closing performances than other switches.With the rise of laser energy,closing delay time and jitter time of double-gap laser-triggered vacuum switch both decrease,while the influences from increasing voltages are weak.Closing delay time of P-P type double-gap laser-triggered vacuum switch can be controlled within 103�1.5 ns under 90 mJ laser energy,and it is about 10 ns longer than single-gap laser-triggered vacuum switch.For some direct current applications with changing voltage directions,P-N type double-gap laser-triggered vacuum switch with 1:1 laser split ratio shows more stable closing per-formances.In addition,closing performances of double-gap laser-triggered vacuum switch can be further improved by optimizing the developments of initial plasma in series gaps.