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The dielectric recovery process has decisive effects on the current interruption process in vacuum circuit breakers, which has attracted the special attention of researchers. In commercial vacuum interrupters, ions and electrons of the residual plasma between the contact gap are separated and then fly to the electrodes under the effect of the transient recovery voltage after current zero. During this period, the post-arc current forms. During the formation of the post-arc current, ions also enter the post-arc anode due to their thermal motion. Therefore, the number of net electrons, which form the post-arc current, is only part of the total electrons between the contact gap at current zero. During the post-arc sheath expansion process, almost all electrons in the contact gap will enter the post-arc anode under the effects of the transient recovery voltage. If the proportion of ions and electrons, which enter the post-arc anode, can be obtained, the total number of electrons and consequently the residual plasma density between the contact gap could be estimated from the integration of the post-arc current. In this paper, the influences on the absorption of charged particles by the post-arc anode of some factors, e.g., rising rate of transient recovery voltage and metal vapor, have been simulated and discussed with a one-dimensional particle in cell-Monte Carlo collision model. [ABSTRACT FROM AUTHOR]

The dielectric recovery process is a crucial stage of current interruption in a vacuum circuit breaker (VCB). The postarc current is an important macroscopic electric characteristic of the dielectric recovery process, which has caused many concerns in the past few decades. In this paper, the postarc currents of VCBs with different types of contacts, such as butt contacts, axial magnetic field contacts, and transverse magnetic field contacts with different materials are measured with a high-resolution current-zero diagnostic system. Besides, the appearance of vacuum arcs is recorded using a high-speed camera in the experiments. The relationship between the arc memory effect and the postarc current is analyzed. What is more, the influence of the instability of the vacuum arc shape on the dispersion of postarc current is also studied. [ABSTRACT FROM AUTHOR]

Initial arc formation in high-current drawn vacuum arc was investigated experimentally and analyzed quantitatively in this paper. Experiments were conducted in a demountable vacuum chamber. Characteristics of molten metal bridges evolution and arc voltage indicated that initial arc formation could be divided into three stages. The correlation between the rupture of molten metal bridges and the fluctuation of arc voltage in stage 2 was analyzed. In addition, characteristics in stage 2 under different arc currents and opening speeds were analyzed quantitatively. [ABSTRACT FROM AUTHOR]

The preparation and storage of aluminum nanoparticles pose significant challenges due to their high chemical reactivity. This paper proposes a one-step method for the production of carbon-coated aluminum nanoparticles using an argon protective arc in a liquid nitrogen environment. The emission spectra of the arc validate that the method proposed in this paper can effectively mitigate the adverse impact of impurity gases such as oxygen and water on the product without the need for expensive vacuum equipment. The obtained nanoparticles underwent characterization through high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman analysis, thermogravimetric analysis, and dynamic light scattering. The characterization results demonstrate the successful synthesis of carbon-coated aluminum nanoparticles with nitrogen-doped fullerene shells. With an increase in arc current, the nanoparticles exhibit a corresponding enlargement in diameter, accompanied by a broader distribution. The characterization of the electrode erosion suggests that the aluminum droplet ejection plays a more important role in the nanoparticle generation process as the arc current increases. Optimized strategies are proposed to increase the percentage of successfully-formed carbon-coated aluminum nanoparticles. • One-step preparation of carbon-coated aluminum nanoparticles. • Arc discharge in liquid environment without vacuum and sealing equipment. • Core-shell structure: Al core wrapped in N-doped fullerenes. • The arc current impacts electrode erosion pattern and product characteristics. [ABSTRACT FROM AUTHOR]

Due to vacuum interrupter's excellent interruption performance, an increasing number of on-load tap-changers (OLTCs) have chosen it as a load changeover switch in recent years. The stability of the arcing process is crucial for the interruption since the vacuum interrupter in OLTC must break current frequently with the requirement of long electrical life. In this paper, experiments on butt contacts and axial magnetic field (AMF) contacts applied in OLTC were carried out in a demountable vacuum chamber, and the arcing process was investigated by a high-speed camera. Investigations were conducted on the effects of opening speed, opening phase, current amplitude, and AMF on arc characteristics, e.g., arc expansion and arc voltage. The experiment findings demonstrated that expansion and instability of arc increased with higher opening speed, number of cathode spots moving to the inclined surface decreased with shorter arcing time, and that cathode spots' propensity to form group cathode spots increased with higher current. AMF lessened the impact of high opening speed and high current on the arcing process. The investigation carried out in this paper helps to better understand the characteristics of arc evolution and the influence of some key factors, which may serve as a guide for improving the design and vacuum arc control of vacuum OLTCs. [ABSTRACT FROM AUTHOR]

In this paper, the evolution of vacuum arc under different conditions in the quench protection switch (QPS) based on forced current zero was investigated experimentally and analyzed quantitatively. Experiments were conducted with cup-shaped axial magnetic field (AMF) contacts in a demountable vacuum chamber. Images of the arc column were photographed through the observation window with a high-speed digital camera with exposure time of 2 μs. Arc appearance was analyzed quantitatively through digital image processing. Quantified arc appearance and arc voltage characteristics indicated that the high-current vacuum arc evolution in the QPS could be divided into four stages: arc formation stage, arc column merging stage, diffusing stage, and fast extinguishing stage. The influence of AMF on the evolution of high-current vacuum arc in the diffusing stage was also studied. Experiment results indicated that the vacuum arc at relatively low current had a simpler evolution process and the arc column merging had less correlation with voltage stability. It was found that the vacuum arc with a long gap distance developed faster and the time required to enter the stable burning state was shorter. In addition, the vacuum arc with long arcing time tended to constrict again, which is not beneficial to current interruption. [ABSTRACT FROM AUTHOR]

Development towards HVDC grids is drawing intense development of HVDC circuit‐breakers (CBs). The increasing rated voltage and capacity requires HVDC CBs with excellent performance to be installed and comprehensive tests on HVDC CBs are indispensable. This paper contributes to clarifying clearer test requirements on the current interruption test, which is the most challenging one and proposing a novel applicable test method. It is the toughest test because when an HVDC CB interrupts fault current, a high transient interruption voltage (TIV) is produced by the operation of metal oxide surge arrester (MOSA), and a large current continues flowing through MOSA simultaneously, which means considerable energy is demanded for the test. To verify an HVDC CB's current interruption ability, voltage withstand ability and energy dissipation ability in single test can be costly and even impractical in extra high voltage classes. Alternatively, a multi‐part test method is reasonable and valuable, in which the HVDC CB can be tested with large current and high voltage one after another, while the energy dissipation ability will be verified separately. At last, a proposed synthetic test circuit is validated by a simulation and a low voltage experiment, creating high equivalence between the simulation and the validation test. [ABSTRACT FROM AUTHOR]

Vacuum circuit breakers (VCB) are commonly used in active mechanical direct current circuit breakers (DC CBs) to accomplish the interruption of the fault current. The post-arc current phenomenon of a VCB is related to the dielectric recovery process of the VCB. Thus, we performed experiments to investigate the influence on the post-arc current by taking the electrode separation, breaking current, and interruption of the bi-directional current with the injecting high frequency current in a fixed direction into account. To be in accordance with the practical interruption duty, the breaking current in the experiment ranges from 500 A to 20 kA. At the same time, the di/dt at current zero (CZ) varies between 200 and 1100 A/μs. The experiment results reveal that the peak value of the post-arc current in an active DC circuit breaker can reach more than 100 A with high di/dt at CZ. It is found that with a longer electrode separation, not only the residual charge increases but also the post-arc current increases. The arcing current before CZ can influence the post-arc current but the effective duration before CZ is short. This duration is the memory time and it is derived from the experiment results. The influence of the breaking current and interruption of the bi-directional current with the injecting current in a fixed direction are dependent on the relation of the current commutation time with the memory time. [ABSTRACT FROM AUTHOR]