Modeling and Simulation of High-Frequency Vacuum Arc Under the Influence of Actual Magnetic Field

The article proposes a mechanical DC circuit breaker (CB) based on a series LC circuit. It requires two switches (a fast disconnector and an AC circuit breaker), an inductor and a capacitor, and therefore the cost is expected to be low. A series LC circuit is analysed and it is concluded that fault current will always have natural zero‐current crossings which enable use of simple AC CBs. The current commutation into a capacitor is investigated since this is important for successful operation. A number of analytical conditions are derived for the voltage stress across disconnector contacts which enable arc‐less contact opening. Experimental results on a 900 V laboratory prototype LC DC CB illustrate successful DC fault clearing, with commutation of 130 A and peak DC current of 190 A. A detailed PSCAD model for 320 kV LC DC CB is developed and DC fault clearing is evaluated in order to understand the possible benefit for high‐voltage direct current applications. Further comparisons with the commercialised hybrid DC CB and mechanical DC CB on 320 kV system illustrate some benefits in terms of performance and simplicity. The mechanical LC DC CB operates very fast because of early capacitor insertion, and this results in low peak current and energy dissipation.

Recently, there has been significant interest in developing the modular multilevel converter (MMC) based DC grids in the power industry. However, the immature DC circuit breaker (DCCB) technology hampers the development of DC grids in overhead lines transmission field. The full controlled power electronic devices based hybrid DCCB has been proposed and researched substantially. But the hybrid type DCCB suffers from the drawback of high cost and low reliability, leading to high capital cost for DC grids that require numerous DCCBs. In this paper, a mechanical type DCCB, consisting of a mechanical switch, a circuit and an oscillation circuit, is proposed. Then, a four-terminal bipolar MMC-HVDC system implementing the mechanical DCCBs is studied. Extensive simulations have been conducted to analyse the transient performance under different fault conditions. The simulation results verify the technical feasibility of this mechanical DCCB in DC grid.

DC circuit breakers are used to achieve fault isolation and clearing of DC systems. It is an essential core equipment for DC network construction. The contact of the vacuum interrupter in the mechanical DC circuit breaker has different magnetic field distribution under different frequency currents. It affects the breaking ability of the breaker at different current frequencies. The cup contact is a commonly used contact in a vacuum interrupter. In this paper, the transient three-dimensional magnetic field distribution of the cup contact at 50~10000Hz current frequency is simulated. The variation of the longitudinal magnetic field distribution along the center of the open center plane with frequency is analyzed. It has been found that the magnetic field lag time of the cup-shaped contact at medium frequency current is large, and it cannot keep up with the change of current. It is too late to establish a longitudinal magnetic field during the arcing process. Therefore, it is similar to the flat contact in the process of breaking the vacuum arc, so that the structure of the cup contact does not play its due role. In order to reduce the magnetic field lag time of the cup contact at medium frequency current, it is necessary to redesign its geometry.

Dc power transmission has been widely used in recent years with low cost, low power and energy loss, high stability and other characteristics, DC power transmission in the technical level there are still some technical obstacles, it for circuit breaker improvement and optimization research level has also received the corresponding attention at home and abroad. As one of the most important components in DC system, DC circuit breaker will become increasingly importan in the future DC transmission technology. In this paper, DC circuit breakers are classified and compared. To combat the present stability issues with circuit breakers in terms of stability, breaking reliability and cost economy, a circuit breaker design scheme based on coupled reactor is proposed. In order to meet the requirements of 500KV DC transmission, the analysis and research of a new coupled mechanical high-voltage DC circuit breaker with current limiting feature are completed. Moreover, PSCAD simulation software is used to verify the scheme's viability through computer modeling. The scheme more effectively inhibits the short-circuit current rise rate and the on-state loss increase, reduces the solid-state switch consumption and capacitor size, so that the cost is better controlled and the low cost and low loss is realized.

DC circuit breaker is of vital importance for security in a high voltage (HV) multi-terminal DC (MTDC) network, particularly in the HV MTDC based on voltage source converters (VSCs) that are typically based on two-level, neutral point clamed (NPC) three-level and modular multilevel. Mechanical DC circuit breaker characterized with low costs and losses has been widely used in the conventional LCC-based HV MTDC network, but cannot be directly applied in the VSC-based HV MTDC due to its slow response and limited breaking capacity. On the other hand, the technology of hybrid DC circuit breaker is immature at present, which has been demonstrated with prototype and cannot be employed in HV (320kV) applications in over ten years. As a result, DC circuit breaker has become an obstacle for HV MTDC development. This paper presents a kind of coordinated operation between mechanical DC breakers and full-bridge sub-module (FBSM) based MMCs to guarantee DC fault ride-through in a HV MTDC network. The proposed coordination strategy is dependent on the DC fault current controllability provided by FBSM-based MMC. Specifically, the capability of FBSM's negative level is adopted to change the common-mode component of MMC arm's reference voltage, which can restrain the fault current to the maximum operation threshold of mechanical DC circuit breaker. This scheme can reduce the demand of breaking capacity and response time for mechanical DC circuit breaker, which thus shows great potential in the applications of HV MMC-based MTDC network. The effectiveness and validity of the coordinated operation is verified by simulation results.

The chapter starts with a short introduction of the research necessity and development history of HVDC circuit breakers and summarizes the functional requirements of HVDC circuit breaker. The working principles of the Hybrid DC circuit breaker, the mechanical DC circuit breaker and the solid-state DC circuit breaker are summarized and described in detail. According to the test requirements of DC circuit breaker, full scale testing method and Metal Oxide Surge Arrester (MOSA) energy absorbing verification by multi-part testing method are proposed, and the application of HVDC circuit breaker in the Nan’ao multi-terminal HVDC system, the Zhangbei HVDC Grid and the Zhou’shan multi-terminal HVDC system are introduced in detail. The operation indicates that the HVDC circuit breaker can accurately and reliably isolate faults and ensure the safe and stable operation of the DC system.

DC Interruption technology is essentially required as DC systems and microgrids have increased. The Interruption technology also includes current limiting technology. Until now, many hybrid Interruption technologies have been proposed in which a semiconductor element or a superconducting element is combined with a mechanical DC circuit breaker. In this paper, an interrupting test was performed by combining a superconductor and a DC circuit breaker. The advantage of circuit breakers combined with superconducting elements is that they do not cause losses and effectively limit the fault current. When the fault occurs, if the fault current exceeds the critical value of the superconducting material, resistance occurs in the superconducting element. The fault current is limited by the resistance generated during quenching and resonates due to the LC divergence oscillation circuit. The current flowing through the mechanical circuit breaker reaches zero-point by resonance. After that, the mechanical breaker is completely opened, and the fault current is interrupted. Superconducting elements exhibit different characteristics depending on their winding method, material, and length. The purpose of this study is to comparatively analyze solenoid and toroid coil type superconducting elements. Both types are made with the same number of turns, permeability, and length. As a result of the experiment, the toroid coil has generated more impedance than the solenoid coil.

Currently, we are developing an AC/DC conversion technology with the development of power semiconductors. Accordingly, DC is attracting attention because it is advantageous in the current transmission system. However, it has a problem that the cut-off technology required for DC system operation has not been secured yet. We are researching and developing a DC cut-off technology in several ways. We proposed a model that combines a superconducting fault current limiter and a DC circuit breaker. This is a configuration which a superconducting fault current limiter and a mechanical DC circuit breaker are connected in series. The superconducting fault current limiter limits the initial fault current and the mechanical DC circuit breaker cuts off the fault current. The mechanical DC circuit breaker consists of a high-speed DC switch, a LC divergent oscillation circuit and a surge arrester. This creates an artificial zero-point by affecting the blocking of the DC fault current according to the LC diverging oscillation circuit. In this paper, we analyzed the effect of the LC divergent oscillation circuit on the superconducting DC circuit breaker according to Reactor (L) and Capacitor (C). As a result, we analyzed the operating characteristics of the superconducting DC circuit breaker according to the application of the LC divergent oscillation circuit using the PSCAD/EMTDC program. Also, we confirmed the characteristics of the initial fault current limit rate of the superconducting fault current limiter and the possibility of controlling how the LC divergent oscillation circuit affects the DC arc generated at the opening of the mechanical DC contacts.

With the rapid development of multiterminal high-voltage direct current (HVdc) transmission systems, the research and development of high-speed and stable high-voltage dc circuit breakers have received attention. Among them, mechanical dc circuit breakers based on manual zero-crossing dc breaking technology have been applied in practical projects, owing to their small size, low on-state loss, and low price. However, this method adds a high-frequency current, which deteriorates the magnetic field between the poles of the interrupter when the arc is broken. Therefore, the development of HVdc circuit breakers that maintain high peak magnetic fields and low residual magnetic fields at high frequencies has become the key to the development of multiterminal HVdc transmission. To solve this problem, this article proposes a new interrupter for a vacuum dc circuit breaker based on artificial zero-crossing technology and studies its key characteristics, such as temperature rise, electromagnetic field, and arc column plasma distribution characteristics. The results reveal that the new interrupter proposed in this article has a low-temperature rise, uniformly distributed electric field, high peak value and low remanence of the longitudinal magnetic field, and uniformly distributed plasma in the arc column, and exhibits arc diffusion. Its ability to cope with high-frequency current is significantly higher than that of the traditional cup-shaped axial magnetic field (AMF) contact system interrupter, which is conducive to the high-speed and stable breaking of the interrupter.

The recovery characteristics of the withstanding voltage of a vacuum gap are crucial for the development of direct circuit breakers with mechanical switches. In the active-current-injection-type dc circuit breakers, a negative voltage, i.e., a voltage of polarity opposite to that of the interrupting current, is initially applied after current zero caused by the energy stored in the active-current-injection branch. Subsequently, the recovery voltage obtains the same polarity as the interrupting current, namely, it becomes positive as the capacitance around the mechanical switch is charged. In this study, the recovery characteristics of the withstanding voltage for the negative and positive polarity are measured by applying impulse voltage after the current zero of dc interruption simulating current. The recovery of the withstanding voltage for a positive impulse takes a longer time than that of the negative impulse. The recovery of the positive withstanding voltage is determined by the decrease in the temperature of the microprojections on the cathode spot edges. The postarc current analysis shows that the postarc plasma decays with time according to the power law in the time range of 1–50 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> after current zero. Under the dc interruptions, where the current decreasing ratio increases, the residual plasma density after current zero tends to be higher than that under ac interruptions.

With the rapid development of Flexible DC transmission technology accompanied with new sources of electricity in recent years, DC circuit breaker, as the core component of DC system protection and control, has received wide attention. As the power source of the circuit breaker, the operating mechanism’s dynamic characteristics have important influence on the DC breaking capacity. Based on the module prototype of mechanical DC vacuum circuit breaker, this paper established DC breaking experiment platform. Main fracture of the prototype was driven by the repulsion mechanism and the vacuum interrupter used the TMF-AMF compound magnetic field contacts. DC short circuit breaking experiments were carried out based on parameter variables such as the opening speed and contact gap. Through the experiments, the images of the DC arc and the curves of arc voltage were observed, the influence of the dynamic characteristics on the DC vacuum arc shape were investigated. The results were analyzed and, it was showed that with the increase of opening speed, arc ignition time is earlier, the acceleration of opening speed will promote vacuum arc to go diffuse, it means that increase the initial opening speed is beneficial to DC breaking under certain conditions. The results can provide theoretical basis for developing DC special vacuum interrupter and improving the DC breaking capacity of the system.

With the announcement of a policy to reduce carbon emissions, the range and technologies of renewable energy sources are increasing. In new renewable energy, the amount and range of solar power generation is relatively gradually expanding[1]. Based on the high-speed DC circuit breaker used in the solar power generation, we combined the LC divergence oscillation circuit and the superconducting element that this research team is working on. This is to protect peripheral equipment against an increase in solar power generation and unspecified disturbances. The DC circuit breaker, we propose is a mechanical DC circuit breaker with a superconducting element applied. The superconducting element can lower the initial fault current within about 2 ㎳ through the quenching operation. However, it takes a large power burden and a long time to cut-off the fault current. In the mechanical DC cut-off part, the existing high-speed mechanical circuit breaker, LC divergent oscillation circuit and Surge Arrestor are connected in parallel to safely and reliably cut off fault current. The characteristics of the cut-off operation that appear when a superconducting element and an LC divergent oscillation circuit are combined with a conventional mechanical DC circuit breaker were analyzed. As a result, through the application of the superconducting element, the speed at which the artificial zero-point of the fault current occurs was reduced, and the time to complete the shutdown was shortened.

The paper presents recent development progress of a mechanical EHV DC circuit breaker with current injection scheme. An EHV level DC circuit breaker composes of multi-break HV vacuum interrupters, a current injection circuit and a metal oxide surge arrester (MOSA) energy absorption unit. The interrupting and energy dissipating performance of HVDC circuit breakers based on current injection scheme were demonstrated at DNV-GL/KEMA laboratory supported by the PROMOTioN projects, funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 691714. A test circuit of DC current interruption uses AC short-circuit generators operated at reduced power frequency, which is capable of providing the stresses evaluated from various DC fault conditions with a simple multi-terminal HVDC grid [1]-[6]. Moreover, a prototype of mechanical HVDC circuit-breaker using a couple of 100 kV vacuum interrupter units was tested in our high power laboratory to demonstrate DC current interruption performance at different current magnitudes ranging from 2 kA to 16 kA with both directions of positive and negative DC currents by creating a current zero immediately after contact separation. The MOSA energy absorption units also showed successfully energy dissipation performance up to 4 MJ with a parallel column arrangement. It will also be demonstrated in PROMOTioN project. The paper will describe the performance and recent development progress in detail.

We proposed a superconducting DC circuit breaker that can reliably cut off the fault currents in preparation for the DC system. It consists of a superconducting element and a mechanical DC circuit breaker. The mechanical DC circuit breaker is connected in parallel with a mechanical high-speed switch, an LC divergence oscillation circuit, and a surge arrester. This provides stable cutoff operation due to the fault-current-limiting operation of the superconducting element and the artificial current zero point of the mechanical DC circuit breaker. In this paper, the operating principle of the LC divergence oscillation circuit that creates an artificial current zero point was reviewed based on the theory. We used experimental data to model the time constant of the initial fault current, the arc model generated by the mechanical high-speed switch, and the experimental equipment. As a result, the LC divergence oscillation circuit was confirmed in the simulation, and simulation modeling was reviewed based on the theoretical principle of generation.

Transformer-type superconducting fault current limiter (TSFCL) interruption system is a current breaking technology proposed by applying a transformer, superconductor, and mechanical dc circuit breaker. When the fault occurs, the fault current is limited due to the operation of the counter electromotive force by the transformer and the quenching of the superconductor. The fault current is then interrupted by the mechanical dc circuit breaker. In this paper, the transition and the interrupting behavior was analyzed according to the applied voltage to secure the stability and reliability of a TSFCL interruption system using the PSCAD EMTDC program. As a result, it was able to improve the current breaking time and the breaking capacity. Also, the burden imposed on a mechanical dc circuit breaker was reduced fivefold.