Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker

When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V–12.33 V drops along the17 μm space charge layer away from the cathode(65.5 k V/m–72.5 k V/m) when the current varies from 20 k A–80 k A.The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core,but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.

Solid-state Circuit Breaker Based on Cascaded Normally-on SiC JFETs for Medium-voltage DC Distribution Networks

Solid-state circuit breakers(SSCBs)are critical components in the protection of medium-voltage DC distribution networks to facilitate arc-free,fast and reliable isolation of DC faults.However,limited by the capacity of a single semiconductor device,using semi-conductor-based SSCBs at high voltage is challenging.This study presents the details of a 1.5 kV,63 A medi-um-voltage SSCB,composed primarily of a solid-state switch based on three cascaded normally-on silicon car-bide(SiC)junction field-effect transistors(JFETs)and a low-cost programmable gate drive circuit.Dynamic and static voltage sharing among the cascaded SiC JFETs of the SSCB during fault isolation is realized using the pro-posed gate drive circuit.The selection conditions for the key parameters of the SSCB gate driver are also analyzed.Additionally,an improved pulse-width modulation cur-rent-limiting protection solution is proposed to identify the permanent overcurrent and transient inrush current associated with capacitive load startup in a DC distribu-tion network.Using the developed SSCB prototype and the fault test system,experimental results are obtained to validate the fault response performance of the SSCB.Index Terms—Solid-state circuit breaker,DC distribu-tion network,SiC JFET,voltage balancing,inrush current.

Magneto-hydrodynamic simulation study of direct current multi-contact circuit breaker for equalizing breaking arc

This work is based on a direct current(DC)natural current commutation topology,which uses load-carrying branch contacts carrying rated current and multiple sets of series arcing branch contacts in parallel to achieve circuit breaking.The proposed topology can meet the new requirements of higher voltage DC switches in aviation,aerospace,energy and other fields.First,a magneto-hydrodynamic arc model is built using COMSOL Multiphysics,and the different arc breaking characteristics of the arcing branch contacts in different gas environments are simulated.Then,a voltage uniformity coefficient is used to measure the voltage sharing effect in the process of dynamic interruption.In order to solve the dispersion of arcing contact action,a structural control method is adopted to improve the voltage uniformity coefficient.The uniform voltage distribution can improve the breaking capacity and electrical life of the series connection structure.

Influence of dc Component during Inadvertent Operation of the High Voltage Generator Circuit Breaker during Mis-Synchronization

This paper analyses the synchronization problem of a generator onto power system without satisfying synchronization condition. The main focus of the paper is on the impact of the dc component of the current in the high voltage circuit breaker during its close-open operating cycle. Using real time measurements of currents/voltages and angles during the close-opening cycle of high voltage generator circuit breaker and the impact of the dc component of current in context of interrupting large magnitude of current from the circuit breaker. In addition, the paper describes a study case model and the results of simulations performed using the software EMTP-ATP of an actual incident that occurred during the inadvertent synchronization of a large 339 MW, 24 kV generator to the grid.

Key stress extraction and equivalent test method for hybrid DC circuit breaker

Firstly, relevant stress properties of millisecond level breaking process and microsecond level commutation process of hybrid HVDC circuit breaker are studied in detail on the basis of the analysis for the application environment and topological structure and operating principles of hybrid circuit breakers, and key stress parameters in transient state process of two time dimensions are extracted. The established digital simulation circuit for PSCAD/EMTDC device-level operation of the circuit breaker has verified the stress properties of millisecond level breaking process and microsecond level commutation process. Then, equivalent test method, circuits and parameters based on LC power supply are proposed on the basis of stress extraction. Finally, the results of implemented breaking tests for complete 200 kV circuit breaker, 100 kV and 50 kV circuit breaker units, as well as single power electronic module have verified the accuracy of the simulation circuit and mathematical analysis. The result of this paper can be a guide to electrical structure and test system design of hybrid HVDC circuit breaker.

A Fault Current Limiting Hybrid DC Circuit Breaker

Due to the low impedance characteristic of the high voltage direct current(HVDC)grid,the fault current rises extremely fast after a DC-side fault occurs,and this phenomenon seriously endangers the safety of the HVDC grid.In order to suppress the rising speed of the fault current and reduce the current interruption requirements of the main breaker(MB),a fault current limiting hybrid DC circuit breaker(FCL-HCB)has been proposed in this paper,and it has the capability of bidirectional fault current limiting and fault current interruption.After the occurrence of the overcurrent in the HVDC grid,the current limiting circuit(CLC)of FCL-HCB is put into operation immediately,and whether the protected line is cut off or resumed to normal operation is decided according to the fault detection result.Compared with the traditional hybrid DC circuit breaker(HCB),the required number of semiconductor switches and the peak value of fault current after fault occurs are greatly reduced by adopting the proposed device.Extensive simulations also verify the effectiveness of the proposed FCL-HCB.

Research on Parameter Collaborative Configuration of DC Circuit Breaker and DC Fault Current Limiter

Fault current suppression is the key technology to ensure the safe operation of the DC power distribution system. In order to realize the parameter collabora-tive configuration of the DC circuit breaker and the DC current limiter and improve the fault current suppression capability, the fault current suppression mechanism of the DC power distribution system is revealed based on the circuit model. Then, based on the mathematical model of the DC breaker, the characteristic parameters of DC breaking are extracted, and then the influence of different characteristic parameters on the breaking characteristics of fault current is studied. Finally, the mathematical model of the collaborative process between DC circuit breaker and DC current limiter is established. The charac-teristic parameters of fault current collaborative suppression are extracted. The coupling effects of different characteristic parameters on the fault current col-laborative suppression are studied. The principle of collaborative configuration of DC circuit breaker and DC current limiter is proposed, and the collaborative suppression ability of DC circuit breaker and DC current limiter to fault current is fully exploited to ensure the safe and reliable operation of the DC power distribution system.

The Study on New Solid-State Breaker and Its Over-voltage Suppression Technique

A design scheme of the intelligent SSB (Solid State Breaker) based on the IGCT (Integrated Gate Commutated Thyris- tor) is presented. The topology of switch module and the structure of the SSB are proposed. Firstly, to the IGCT’s over-voltage sensitivity problem, a new technique of reducing the over-voltage is introduced, which releases the elect romantics energy of faulty line by a capacitive current branch to reduce the amplitude of over-voltage. Secondly, the principle of over-voltage suppression with current release branch is analyzed, and the overall control scheme of solid- state breaker is put forward. Finally, the simulation results also demonstrate its obvious effectiveness in over-voltage suppression after adding a current release branch into the SSB.

SiC JFETs Modular Cascaded Method with Active Clamp Control Strategy for DC Solid-state Circuit Breaker

Power semiconductor devices cascaded topology is one of the most common solutions for solid-state circuit breakers(SSCBs)working in medium-voltage DC systems.However,when the number of cascaded devices is large,current series technologies of power semiconductor devices will be difficult to be applied since with uneven voltage sharing problems.Thus,this paper proposes a novel cascade method of multi-SiC JFETs based on modules cascaded.This method consists of two parts:one is a single-gate driver cascaded SiC JFETs topology which is used to form the module,the other one is an active clamp control strategy which ensures that each module is protected from overvoltage when modules are cascaded.The proposed cascade method can effectively suppress voltage overshoot of cascading power devices in the switching process.Based on the proposed cascade method,a 5kV/63A SSCB prototype is designed.Finally,an experiment is conducted based on the designed SSCB.Experimental results validate the effectiveness of the proposed cascaded method for SSCB.

Numerical Study on Arc Plasma Behavior During Arc Commutation Process in Direct Current Circuit Breaker

This paper focuses on the numerical investigation of arc plasma behavior during arc commutation process in a medium-voltage direct current circuit breaker （DCCB） contact system. A three-dimensional magneto-hydrodynamic （MHD） model of air arc plasma in the contact system of a DCCB is developed, based on commercial software FLUENT. Coupled electromagnetic and gas dynamic interactions are considered as usual, and a thin layer of nonlinear electrical resistance elements is used to represent the voltage drop of plasma sheath and the formation of new arc root. The distributions of pressure, temperature, gas flow and current density of arc plasma in arc region are calculated. The simulation results indicate that the pressure distribution related to the contact system has a strong effect on the arc commutation process, arising from the change of electrical conductivity in the arc root region. In DCCB contact system, the pressure of arc root region will be concentrated and higher if the space above the moving contact is enclosed, which is not good for arc root commutation. However, when the region is opened, the pressure distribution would be lower and more evenly, which is favorable for the arc root commutation.

Vacuum Dielectric Recovery Characteristics of a Novel Current Limiting Circuit Breaker Base on Artificial Current Zero

为了保证新型强迫换流型真空直流限流断路器关断短路电流的可靠性，对该型断路器分断过程的真空介质恢复特性进行研究。设计了与断路器关断过程等效的介质恢复试验方案，通过等效试验结果和理论推演公式的拟合，得到了新型强迫换流型限流断路器真空灭弧室触头打开过程的动态介质强度恢复规律。研究结果表明：减小燃弧能量、提高触头运动速度可提高真空灭弧室介质的临界击穿电压；综合考虑燃弧时间与燃弧能量及触头开距的关系，随着燃弧时间的增加，真空灭弧室临界击穿电压先减小后增大。所得介质恢复规律可以作为新型断路器优化设计的参考依据。

Research on arc root stagnation when small current is interrupted in self-excited circuit breaker

The self-excited DC air circuit breaker(SE-DCCB)has been widely used in urban rail transit due to its excellent stability.It can realize forward and reverse interruption,but has difficulty interrupting small currents due to the phenomenon of arc root sticking at the entrance of the arc chamber in the splitting process,which is known as arc root stagnation.A coupling model of the self-excited magnetic field and magnetohydrodynamics is established for the SE-DCCB with the traditional structure.The magnetic field,temperature and airflow distribution in the arc chamber are investigated with an interrupting current of 150 A.The simulation results show that the direction and magnitude of the magnetic blowout force are the dominant factors in the arc root stagnation.The local high temperature of the arc chamber due to arc root stagnation increases the obstruction effect of the airflow vortex on the arc root movement,which significantly increases the arc duration time of small current interruption.Based on the research,the structure of the magnetic conductance plate of the actual product is improved,which can improve the direction and magnitude of the magnetic blowout force at the arc root so as to restrain the development of the airflow vortex effectively and solve the problem of arc root stagnation when the small current is interrupted.The simulation results show that the circuit breaker with improved structure has a better performance for a small current interruption range from 100 A to 350 A.

基于电弧磁流体仿真的DC 1500V两极塑壳断路器气道优化设计

该文开发了用于DC 1500V光伏和储能系统的新一代两极直流塑壳断路器样机。通过DC 1500V/15 kA,时间常数10 ms的短路分断实验发现,电弧电压快速升至350 V是提升断路器限流和分断性能的关键。为了加快初始燃弧阶段电弧运动速度使弧压快速上升,建立了断路器触头区域的二维局部电弧磁流体仿真模型,通过分析灭弧室温度、压力分布和气流速度变化曲线,明确了初始样机中电弧运动停滞的机理,并以此为依据提出了参差栅片排布和添加导流锥的气道优化设计方案。使用优化后的样机进行分断实验,比较优化前后的电压变化曲线和电弧运动高速摄像,验证了优化方案的有效性,对于DC 1500V两极直流塑壳的设计开发具有很强的实践指导意义。

直流故障下MMC-HVDC的两段式限流保护策略

如何对直流故障电流进行有效抑制是实现柔性直流电网大规模发展的关键。为此,研究模块化多电平变换器(modular multilevel converter,MMC)的控制方法,提出一种针对半桥型MMC的两段式限流保护策略,通过减少子模块的投入数目来降低换流站直流出口电压,达到限制短路电流的目的。首先,介绍MMC的拓扑结构及基于MMC的高压直流输电(MMC based high voltage direct current,MMC-HVDC)系统控制策略;其次,分析两段式限流保护策略的原理与直流故障电流特性,介绍MMC-HVDC系统的直流故障保护策略;最后,通过双端MMC-HVDC系统仿真实验,对所提限流保护策略的有效性进行验证。仿真结果表明,两段式限流保护策略可以有效降低断路器开断电流和吸收能量,节约成本。

Coordinated Control of DC Circuit Breakers in Multilink HVDC Grids

High voltage DC grids are developing in more terminals and with larger transmission capacity,thus the re-quirements for DC circuit breakers(DCCB)will continue to rise.Conventional methods only use the faulty line DCCB to withstand the fault stress,and therefore this paper presents a coordination method of multiple DCCBs to protect the system.As many adjacent DCCBs are tripped to interrupt the fault current,the fault energy is shared,and the requirement for the faulty line DCCB is reduced.Moreover,the adjacent DCCBs are actively controlled to help system recovery.The primary protection,backup protection,and reclosing logic of multiple DCCBs are studied.Simulations confirm that the proposed control reduces the energy dissipation requirement of faulty line DCCB by approximately 30%-42%,the required current rating for IGBTs is reduced,and the system recovery time is also reduced by 20-40 ms.

Review on Z-Source Solid State Circuit Breakers for DC Distribution Networks

DC technologies will be essential building blocks for future DC distribution networks.As in any DC system,these networks will face crucial threats imposed by short-circuit DC faults.Protection is thus of great interest,and it will likely rely on DC circuit breakers(DCCBs).Among available configurations,Z-source solid-state circuit breakers(Z-SSCBs)are promising candidates for protecting low and medium-voltage distribution networks,as well as DC equipment due to their structural and control simplicity and low cost.In this paper,start-ofthe-art of Z-SSCBs topologies is reviewed.To set the context,the use of DC technologies for grid integration of renewables,DC power transmission,and the main types of DCCBs to protect DC transmission and distribution corridors are discussed.The Z-SSCB topologies are then classified into unidirectional and bidirectional.Advantages and disadvantages of different configurations are compared and analyzed based on existing research.Finally,a perspective on the future development of Z-SSCBs is discussed and potential challenges are elucidated.

Study on TRV of circuit breaker in two substation operational ways and its countermeasure

To verify a vacuum breaker's feasibility,when a transformer substation chooses a vacuum circuit breaker,it takes two different actual operational ways to cut off a transformer.This paper,using the power system computer aided design/electro magnetic transient in DC system(PSCAD/EMTDC)software,simulates the substation system and studies transient recovery voltage(TRV)caused by the two different ways which can cut off a with load transformer or a no-load transformer.Simulation and calculation results show that TRV indexes of the first way are much higher than that of the second one,and their TRV indexes are both in a permissible range.The breaker is proved to be available.Besides,this paper proves that paralleling resistance has a good effect when the indexes exceed the standard.The resistance value depends on specific circumstances.

Adaptive Reclosing Scheme Based on Traveling Wave Injection For Multi-Terminal dc Grids

The hybrid dc circuit breaker(HCB)has the advantages of fast action speed and low operating loss,which is an idealmethod for fault isolation ofmulti-terminal dc grids.Formulti-terminal dc grids that transmit power through overhead lines,HCBs are required to have reclosing capability due to the high fault probability and the fact that most of the faults are temporary faults.To avoid the secondary fault strike and equipment damage that may be caused by the reclosing of the HCB when the permanent fault occurs,an adaptive reclosing scheme based on traveling wave injection is proposed in this paper.The scheme injects traveling wave signal into the fault dc line through the additionally configured auxiliary discharge branch in the HCB,and then uses the reflection characteristic of the traveling wave signal on the dc line to identify temporary and permanent faults,to be able to realize fast reclosing when the temporary fault occurs and reliably avoid reclosing after the permanent fault occurs.The test results in the simulation model of the four-terminal dc grid show that the proposed adaptive reclosing scheme can quickly and reliably identify temporary and permanent faults,greatly shorten the power outage time of temporary faults.In addition,it has the advantages of easiness to implement,high reliability,robustness to high-resistance fault and no dead zone,etc.

Circuit breakers in HVDC systems: state-of-the-art review and future trends

High voltage direct current(HVDC)systems are efficient solutions for the integration of large-scale renewable energy sources with the main power grids.The rapid development of the HVDC grid has resulted in a growing interest in DC circuit breakers(DCCBs).A fast and reliable circuit breaker is a necessary requirement in the development of large scale HVDC grids.This paper provides a comprehensive review and survey of the HVDC CBs and discusses potential research directions.Operational principles and the main features of various DCCBs are described and their merits and shortcomings are also highlighted.

基于固态断路器主动注入式直流故障测距方法

随着直流配电网的快速发展与深化应用,准确可靠的故障测距技术对直流故障检修和恢复至关重要。该文提出一种基于固态断路器(SSCB)主动注入式直流故障测距方法。首先,利用SSCB开断主动注入不同脉冲宽度的信号,并检测注入脉冲首末端和反射波首末端的时间差作为注入波形传播时间间隔,能够减小采样频率带来的误差。然后,提取电缆线路电压线模量作为检测量,削弱正负极线路之间的耦合作用,获得稳定波速。最后,基于小波变换原理提出改进自适应模极大值方法来检测脉冲首末端时刻,减小噪声和过渡电阻对测距精度的影响。仿真结果表明,基于SSCB主动注入式测距方法在直流配电网单极接地和极间短路故障情况下均能够实现准确且快速的定位。