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The amplitude and rise time of fault currents can be reduced by installing a resistive-type superconducting fault current limiter (SFCL) in a voltage-source converter high-voltage DC (VSC-HVDC) system. Such an SFCL can provide sufficient time for a mechanical-type dc circuit breaker to interrupt a fault current. The objective of this paper is to elucidate the dc-current-limiting characteristics of Yttrium Barium Copper Oxygen (YBCO)-coated conductor tapes for a wide range of prospective currents (ranging from 50 to 10 kA). The factors investigated include critical currents (Ic) of the tape of 102 and 225 A, circuit time constants of 1 and 3 ms, and rated dc voltages of 250 and 500 V. The experimental results show that the limited current remains nearly constant with prospective current when the prospective current is higher than ten times Ic. The circuit time constant affects only the peak value and rise rate of the limited current. A single tape (I c = 102 A) can limit a 10-kA prospective current to a peak value of 555 A. The limited current for a rated voltage of 500 V is always higher than that for a rated voltage of 250 V. [ABSTRACT FROM PUBLISHER]

• We explored short-circuit current interruption characteristics of a double-break FVCB within the minimum arcing time. • The minimum arcing time and the critical arc extinguishing contact gap of the double-break FVCB decreased with the increase of the opening velocity. • The uneven voltage distribution in minimum arcing time short-circuit current interruption was mainly caused by stray capacitance. • For failure interruptions, the two breaks were all asynchronous breakdowns. After the breakdown of the upper break, even if the insulation was recovered, it still could not withstand the voltage before the breakdown. • Capacitive current and field-induced emission current jointly determined the voltage development of the two breaks after the breakdown of the upper break. It is significant for circuit breakers to expel a short-circuit fault in a short time for the new power grid with high proportional photovoltaic or wind power plants to achieve high transient operating stability. Compared with a traditional circuit breaker, a fast vacuum circuit breaker (FVCB), operated by an electromagnetic repulsion actuator, has an extremely shorter opening time and lower deviation in their opening times. This potentially contributes the FVCBs to interrupting a short-circuit fault current in the first half-wave when introducing a controlled switching technology. Meanwhile, it is beneficial to improve the short-circuit current breaking capacity of the FVCBs by adopting series-connected double-break circuit breaker technologies. This paper aims to explore short-circuit current interruption characteristics of a double-break FVCB within the minimum arcing time. We performed a series of short-circuit current interruption tests in a Weil synthetic test circuit. Two series-connected FVCBs and independent single-break FVCBs were used. Three different kinds of opening velocities were adopted for each of the FVCBs. Results showed that the increase in opening velocity resulted in both a decrease in the minimum arcing time and the critical arc extinguishing contact gap, whether for the single-break or the double-break interruption tests. The ratio of the shared voltage on each of the series-connected FVCBs was about 54 (for the break on the high-voltage side) and 9 (for the break on the low-voltage side). Taking the break with a shorter opening time as a break in the high-voltage side could reduce the minimum arcing time and the critical arc extinguishing contact gap. At the same opening velocity, the sum of the critical arc extinguishing contact gap of the two breaks in double-break interruption tests was significantly higher than twice the critical arc extinguishing contact gap in the single-break interruption tests. This could be caused by the fact that in double-break interruption tests, after the breakdown of one break, even if the break restored insulation, could not share the transient recovery voltage (TRV) before the break broke down. In addition, the sudden drop of TRV without breakdown occurred for the break on the high-voltage side might correlate with the micro-discharge of the vacuum gap. The interaction of the charged particles with the electrode surface would be responsible for the formation and evolution of the micro-discharge in some successful interruption cases. [ABSTRACT FROM AUTHOR]

According to the vacuum breakdown model based on Cranberg “clump” hypothesis, micro-particles on contact surface can be detached from the contact surface and accelerated across the vacuum gap towards to the opposite contact under an applied voltage in vacuum interrupters (VIs). Finally they can impact on the target contact surface with high velocities, which probably triggers a breakdown in the vacuum gap. Thus, the mechanism of the impact phenomena may be the key to understanding the mechanism of the vacuum breakdown initiated by the micro-particles. Moreover, the detailed nature of the dynamic impact process is a subject of the hydro-dynamical theories on the projectile impact. The objective of this paper is to study the micro-particles impact phenomena in VIs by introducing a mesh-free numerical calculation method Smoothed Particle Hydrodynamics (SPH) method which is an efficient method of the projectile impact studies. In this paper, the materials of the micro-particle and the target contact were assumed to be copper and stainless-steel, respectively. The radius of the micro-particle was assumed to be 0.1 µm. The characteristics of the deformations occurring during the high-velocity impact processes are investigated under the different applied voltages (10 to 60 kV). As a result, it is found that the deformations of the micro-particles and the target contacts are severer with the increase of applied voltages, due to the increase of the impact velocities. With the applied voltages 50 kV and even to 60 kV (the impact velocity 526 and 631 m/s), there can be damages generated on the contact surface accompanying by a large number of high-velocity secondary particles. Furthermore, the influencing factors of the micro-particles impact phenomena in VIs, such as the size of the micro-particles, the microscopic electric field distribution, the contact materials and so on, have also be considered. The result of this paper may provide some useful information to understand the vacuum breakdown initiated by the micro-particles. [ABSTRACT FROM AUTHOR]

Inside a high-voltage vacuum interrupter, multiple floating shields form the multiple vacuum gaps (VGs) in series. When the number of series VGs exceeds three, there will exist floating potential VGs in which both electrodes have floating potentials. The floating potential VG is important for the dielectric strength of multiple VGs in series. The objective of this paper is to quantitatively determine the effect of the floating potential VG distance on the breakdown (BD) characteristics of triple VGs in series. In the experiments, triple VGs were built up by series-connecting three pairs of sphere-plane electrodes vertically. A negative standard lightning impulse voltage (1.2/50 μs) was applied. The experimental results revealed that a critical gap distance of the floating potential VG was required to support the dielectric strength of triple VGs in series. The distance was approximately 0.7 mm in this experiment. The critical distance of the floating potential VG can be determined by an intersection of the maximum electric field strength at cathode and the 100% BD electric field strength of the floating potential VG. This method can be used to estimate the critical distance of the floating potential VG in a high-voltage vacuum interrupter. • Quantitatively investigate the effect of floating potential VG distance on BD characteristics of triple VGs in series. • Determine a critical gap distance of the floating potential VG in triple VGs in series. • Propose a method to estimate the critical distance of the floating potential VG. [ABSTRACT FROM AUTHOR]

• Determining the influence of the prestrike characteristics of four types of VCBs combined with two types of controlled switching strategies on the suppression effect of the inrush current. • Proposing a novel controlled switching strategy which the closing command depends on the 50% pre-arcing time t a50 of the VCBs. • The spiral-type TMF double-break VCB combined with the novel controlled switching strategy is the best choice for applying back-to-back capacitor bank controlled switching. Controlled switching of capacitor banks is an effective way to suppress the inrush current during capacitive-making operations. The objective of this paper is to determine the influence of the prestrike characteristics of four types of vacuum circuit breakers (VCBs) combined with two types of controlled switching strategies on the suppression effect of the inrush current. The four types of VCBs are cup-type axial magnetic field (AMF) single-break VCB, spiral-type transverse magnetic field (TMF) single-break VCB, cup-type AMF double-break VCB and spiral-type TMF double-break VCB. The prestrike characteristics of the four types of VCBs are investigated by synthetic tests. The two types of controlled switching strategies are the traditional controlled switching strategy (the closing command depends on the mechanical touch instant of the two contacts in VCBs) and the novel controlled switching strategy (the closing command depends on the 50% pre-arcing time t a50 of the VCBs). The results show that the spiral-type TMF double-break VCB combined with the novel controlled switching strategy is the best choice for applying back-to-back capacitor bank controlled switching. © 2017 Elsevier Inc. All rights reserved. [ABSTRACT FROM AUTHOR]

Plasma electrolytic oxidation process is a surface modification technique using plasma-assisted oxidation to prepare the protective layers that improve the surface performances of valve metals such as aluminium, magnesium, and titanium. However, there is poor understanding and ability to control the process, and many uncertainties. The main objective of this paper is to present the discharge behavior with windmill structure, stable group movement and long-term stability. All processes were carried out on 6061 aluminium alloy by applying a bipolar pulsed current with a frequency of 200 Hz, positive and negative pulse durations of 2 ms, and equal pulse pauses. Utilizing current pulses having equal amplitudes between the positive and negative periods resulted in destructive discharges in the late stage. By adjusting the average positive current at a certain time, destructive discharges were eliminated. Meanwhile, various windmill discharge migration patterns were established, in which collective discharges aggregated into several clusters and rotated as a whole on the sample surface. The number of the clusters was correlated to the average positive current. A complete plasma electrolytic oxidation process was proposed to produce a series of coatings, in which the average positive current was reduced at a rate of 0.1 A·min−1 from 95 min to 100 min, and the windmill discharge migration pattern gradually emerged after 100 min. The proposed method increased the treatment duration from ~95 min to ~180 min compared to the process with no current adjustment. In addition, the thickness, relative content of α- and γ-Al 2 O 3 phases, and Vickers hardness of the coatings were significantly enhanced, allowing for the preparation of high-quality coatings. [Display omitted] • Plasma discharges aggregate into several clusters and rotate as a whole. • Adjusting positive current changes discharge migration pattern. • Reducing positive current eliminates destructive discharges. [ABSTRACT FROM AUTHOR]

• A novel UN-CN is proposed for few-shot HVCB fault diagnosis. • U-net is introduced to extract discriminative features with insufficient samples. • Capsule network is used to reduce feature loss and solve the few-shot problem. • The dynamic routing algorithm is employed for model optimization. • The results demonstrate the superiority of UN-CN in few-shot fault diagnosis. Deep learning methods have achieved noteworthy seeing results in the mechanical fault diagnosis of high-voltage circuit breakers with the recent advancements in artificial intelligence. However, the premise of the above method for obtaining excellent performance is to have sufficient samples, which is impractical due to the characteristics of the high-voltage circuit breakers. This study proposes a novel U-Net with CapsNet for high-voltage circuit breakers fault diagnosis to resolve these issues, achieving a high-precision and robust diagnosis of few-shot high-voltage circuit breakers. In a few-shot diagnosis, the U-Net with CapsNet takes advantage of the high accuracy of the U-Net. The capsule network is used in the contraction and expansion paths of the original U-Net to reduce the loss of features in the pooling process. The forward transfer from the bottom to the high-level capsule is completed by the dynamic routing algorithm. The feature information in the high-level capsule is unified with the bottom layer. The experimental results show that using the U-Net with CapsNet proposal, we can quickly and accurately realize the fault diagnosis of few-shot high-voltage circuit breakers, with an accuracy of 93.25%. The model has faster convergence speed and better stability, which provides a reliable solution for efficient and accurate fault diagnosis of high-voltage circuit breakers compared with traditional methods. [ABSTRACT FROM AUTHOR]

[Display omitted] Previous studies mainly focused on the prestrike phenomena in single-break vacuum circuit breakers (VCBs) under capacitive switching. However, experimental investigations on prestrike characteristics under capacitive making operations of double-break VCBs were not addressed in literatures, which were important for the strategies of capacitive controlled switching. The objective of this paper is to experimentally investigate the prestrike characteristics of single-break and double-break VCBs in switching capacitor banks, to determine the most suitable type of VCBs in capacitive switching. The double-break VCB consists of two commercial 12 kV vacuum interrupters (VIs) with cup-type axial magnetic field (AMF) contacts, which is the same VI in the single-break VCB. The results show that the 50% prestrike gap d 50 of each VI in the double-break VCB, which was calculated based on the complementary Weibull distribution, was significantly reduced by 10.5% compared with the single-break VCB. Due to the voltage-sharing effect in the double-break VCB, scatters in prestrike gaps of the double-break VCB were smaller than the single-break VCB. With the application of the double-break VCB, both the inrush current interruption and the prestrike arcing time can be reduced. The double-break VCB can reduce the erosion caused by the inrush current of the low-voltage side VI. In capacitive switching, the double-break VCB is superior to the single-break VCB, especially in capacitive controlled switching. [ABSTRACT FROM AUTHOR]

• Building the arc reignition model of a 40.5-kV vacuum circuit breaker. • Simulating the overvoltage caused by switching off shunt reactors in the 35-kV substation. • Studying the impact of five types of overvoltage suppression measures in identical systems and vacuum circuit breaker conditions. • The suppression effects in descending order are the phase-controlled vacuum circuit breaker, adding surge arresters, adding RC snubbers, double-break vacuum circuit breaker and increasing the cable length. Shunt reactors are commonly used in substations to compensate the capacitive reactive power of electric power systems. When a vacuum circuit breaker (VCB) switches off shunt reactors, an overvoltage with high amplitude and high frequency (HF) is generated because of the current chopping and multireignition of the VCB. The objective of this paper is to build the 40.5 kV statistical VCB model, simulate the overvoltage caused by switching off shunt reactors in a 35 kV substation, and analyze the impact of five types of overvoltage suppression measures under identical VCB conditions and substations. The statistical VCB model is established in MATLAB/Simulink and verified by the field tests. Three basic factors are considered in this model: chopping current value, dielectric dynamic insulation strength and HF current quenching capability of the VCB. The simulation results show that the suppression effects in descending order are the phase-controlled VCB, adding surge arresters, adding RC snubbers, double-break VCB and increasing the cable length. [Display omitted] [ABSTRACT FROM AUTHOR]

• LN 2 has 2–2.7 and 1.4–1.8 times higher FOVs in comparison to the air and oil insulation. • The +ve and -ve lightning impulse tests have almost the same surface flashover characteristics. • The EFD simulations of 12 kV umbrella and smooth type VI bottles have no significant difference. • Umbrella type VIs are recommended for the superconducting power switchgear applications. • The findings can provide a good reference to the VI manufacturing industry. Liquid Nitrogen Insulated metal enclosed Switchgear (LNIS) is a new type of power switchgear system. It uses liquid nitrogen (LN 2) as coolant, insulation and arc quenching medium. LNIS mainly consists of resistive type superconducting fault current limiter (R-SFCL), LN 2 isolator switch and Vacuum circuit breaker (VCB). Vacuum interrupters (VIs) are used in combination with magnetic actuator to operate as VCB in LNIS. This paper deals with the surface flashover investigations of VI in LNIS. For fair comparisons, two types of standard manufacturing, 12 kV, VI modules, namely; Smooth type and Umbrella type, were selected and tested in open air, transformer oil (also known as Hydro-treated Light Naphthenic Distillate) and LN 2 environments under the standard lightning impulses, i-e positive and negative. Therefore, a total of 12 comparisons have been reported in this paper. Up and down method has been followed and Statistical analysis have been done for all types of tests. Weibull and Box & Whiskers plots reveal some important results with accumulated probabilities from 0% to 100% Flashover voltages (FOVs), the most important be the critical FOV, also known as 50% Flashover voltages (U50). The results reveal that, for Air tests, the 12 kV smooth type VI has a U50 range of 109–121 kV and Umbrella type is 98–123 kV. In transformer oil tests, the 12 kV smooth type VI has a U50 range of 161–164 kV and Umbrella type is 161–168 kV. In addition, For LN 2 tests, the 12 kV smooth type VI has a U50 range of 232.5–282 kV while Umbrella type is 256–260 kV respectively. The 200 shoots survival tests were also done on three smooth type and 3 umbrella type VI bottles. Electrical distribution simulations were carried out to compare the experimental results with the simulation results. All types of tests were done at least 200 times or when the results became stable. It was also observed that the FOVs gets higher after 100 tests due to conditioning process. Lastly, it was observed that Umbrella type VIs are more suitable for LNIS applications because of its mechanical toughness and overall higher range of FOVs. The results documented in this paper will play an important role in designing the overall structure of LNIS. VI manufacturing companies are expected to take advantage of these findings for their design of VIs in Air, Transformer Oil and LN 2 environments because the literature lacks such results about VIs until now. [ABSTRACT FROM AUTHOR]

Due to the high-temperature nature of SiC, SiC MOSFETs can encounter a unique gate failure in SC operation at temperatures below the limit of thermal runaway. This paper aims to identify the two distinct failure modes of SiC planar MOSFETs under specific SC conditions based on the understanding of electro-thermal-mechanical failure physics. The SC failure mode depends on the heating rate and time of two key zones: the source Al adjacent to the upper side of the inter-metal dielectric and the hot spot inside the semiconductor near the JFET region. A 1D multilayer thermal model is used to estimate the transient temperature of the two locations and is validated for a wide range of V DS (from 200 V to 800 V). The model can also predict the failure mode and SCWT using a short turn-on pulse. • Identification of the two distinct failure mechanisms during short-circuit of SiC MOSFETs • Clarification of the failure thresholds based on electro-thermal-mechanical failure physics • Failure mode prediction by simplified multi-layer thermal modeling [ABSTRACT FROM AUTHOR]

Data-driven diagnosis methods have been systematically investigated for the diagnosis of gas-insulated switchgear (GIS) partial discharge (PD). However, because of the scarcity of samples on-site, an operational gap exists between the diagnostic methods and their actual application. To settle this issue, a novel metric-based meta-learning (MBML) method is proposed. First, a hybrid self-attention convolutional neural network is constructed for feature extraction and trained through supervised learning. Then, the episodic MBML is used to train other parts, and the metric classifier is employed for diagnosis. The proposed MBML exhibits an accuracy of 93.17% under 4-way 5-shot conditions, which is a significant improvement over traditional methods. When the number of support sets is small, the benefits of MBML are more prominent, providing a viable solution for the on-site diagnosis of PD in GISs., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 ISA. Published by Elsevier Ltd. All rights reserved.)

The study on the mechanism of the effect of temperature on the decomposition reaction of SF n (n = 1-6) under discharge conditions is very important in studying the potential fault of SF 6 high voltage switch equipment and perfecting the chemical kinetic model of SF n discharge. In this paper, structural optimizations, thermal correction to Gibbs free energy for the reactants, and products were performed at the B3LYP/6-311 +  + G(d,p) theory level. The single-point energies of all species were collected at the CCSD(T)/aug-cc-PVTZ level. The electric and thermal decomposition mechanism of SF n under discharge conditions of 298-10,000 K were studied, respectively. The conclusion drawn was that in the temperature range of 298-10,000 K, the thermal decomposition homopolytic reaction △G began to decline from 200 kJ/mol, while the △G of the other two heterogenous reactions began to decrease from 1000 kJ/mol and 2000 kJ/mol, showing a downward trend of an almost similar slope. The electrolysis of SF n is related to electron energy. When the electron energy is low, SF n  + e → SF n - series reactions occur, and △G of R12, R20, R28, R36, and R44 increases with temperature rise, while △G of R4 decreases with temperature. When the electron energy is high, one of SF n -  → SF n-1 -  + F, SF n -  → SF n-1  + F - , and SF n -  → SF n-1  + F + e will occur, and the reactions that occur at various temperature ranges as the temperature rises vary. When the second electron hits the SF n - , the SF n -  + e → SF n-1 -  + F reaction will occur. The △G of this reaction slowly decreases with an increase in temperature. This study in clearer terms explains the decomposition process and mechanism of SF n at different temperatures., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

Sufficiently high voltage applied between two metal electrodes, even in ultra high vacuum conditions, results in an inevitable discharge that lights up the entire gap, opening a conductive channel through the vacuum and parasitically consuming large amounts of energy. Despite many efforts to understand the processes that lead to this phenomenon, known as vacuum arc, there is still no consensus regarding the role of each electrode in the evolution of such a momentous process as lightning. Employing a high-speed camera, we capture the entire lightning process step-by-step with a nanosecond resolution and find which of the two electrodes holds the main responsibility for igniting the arc. The light that gradually expands from the positively charged electrode (anode), often is assumed to play the main role in the formation of a vacuum arc. However, both the nanosecond-resolution images of vacuum arc evolution and the corresponding theoretical calculations agree that the conductive channel between the electrodes is built in the form of cathodic plasma long before any significant activity develops in the anode. We show evidently that the anode illumination is weaker and plays a minor role in igniting and maintaining the conductive channel.

N 2 has been introduced to gas-insulated switchgears (GIS) as an environmentally friendly insulation medium for SF 6 gas. Considering the low breakdown strength of N 2 , it's essential to apply a dielectric coating on part of the electrode in GIS. In the current work, yttria-stabilized zirconia (YSZ) and zirconia-toughened alumina (ZTA) ceramics are tactfully applied as dielectric coating materials and successfully coated on the surface of rod electrode via high efficiency supersonic atmospheric plasma spraying method. It is demonstrated that both YSZ and ZTA have excellent thermal stability. In the measured frequency range 10 -2 -10 6  Hz, the dielectric constant (ε') decreases with the increase in frequency. At measured temperatures (0-140 °C), ε' increases from 15.45 to 16.31 for YSZ ceramic at 1 kHz, while it varies between 30.23 and 39.34 for ZTA ceramic. As compared to that of bare electrode, the 50% BDV (U 50 ) of solid/gas composite insulation system is significantly improved when using YSZ and ZTA as coating materials. Furthermore, the U 50 increases with the increase of coating thickness. For the electrode coated with ZTA ceramic (500 μm), the U 50 value reaches to 86 kV, which is enhanced about 21.13% in comparison with that of bare electrode. With respect to YSZ ceramic coating (500 μm), a higher U 50 value of 88 kV is obtained. This is mainly due to that YSZ has a lower permittivity, which can generate a more uniform electric field distribution between the rod and plane electrodes, bringing about a higher breakdown voltage.

An innovative array of magnetic coils (the discrete Rogowski coil-RC) with the advantages of flexible structure, miniaturization and mass producibility is investigated. First, the mutual inductance between the discrete RC and circular and rectangular conductors are calculated using the magnetic vector potential (MVP) method. The results are found to be consistent with those calculated using the finite element method, but the MVP method is simpler and more practical. Then, the influence of conductor section parameters, inclination, and eccentricity on the accuracy of the discrete RC is calculated to provide a reference. Studying the influence of an external current on the discrete RC's interference error reveals optimal values for length, winding density, and position arrangement of the solenoids. It has also found that eccentricity and interference errors decreasing with increasing number of solenoids. Finally, a discrete RC prototype is devised and manufactured. The experimental results show consistent output characteristics, with the calculated sensitivity and mutual inductance of the discrete RC being very close to the experimental results. The influence of an external conductor on the measurement of the discrete RC is analyzed experimentally, and the results show that interference from an external current decreases with increasing distance between the external and measured conductors., Competing Interests: The authors declare no conflict of interest.