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.

Direct Current Circuit Breaker in EAST

This paper introduces the configuration and the operation principles of a high power direct current circuit breaker （DCCB）. The commutating current principle of the breaker is described in details with its theory and simulation analysis. The test results presented show that the DCCB meets the requirements for quenching protection. It will be used as the main breaker for quench protection in EAST.

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.

基于钳位型断路器的柔直系统控保协同技术

柔性直流系统以其在输电领域的巨大优势而获得广泛应用.但在直流系统中,短路故障的强冲击性与电力电子器件的脆弱性之间的矛盾异常尖锐,现有保护策略难以同时满足高速动性与高可靠性的要求.本文从控保协同思想出发,基于一种电压钳位原理的直流断路器,提出一种新的故障处理模式,初步探究在柔直系统中控制与保护深度融合的可能性.当发生短路故障时,投入断路器和换流器相配合的限流功能,一方面限制电力电子器件的过流,解决其脆弱性问题;另一方面为保护提供边界,辅助实现故障的快速定位.在甄别出故障线路后,利用断路器的故障切除功能将故障隔离.此方案同时实现了故障限流、保护边界和故障切除3项功能,可有效缓减由于模块化多电平换流器(modular multilevel converter,MMC)器件脆弱性所带来的一系列保护问题.在PSCAD/EMTDC中搭建四端双极柔性直流电网模型,仿真结果表明,本控保协同方案能在5 ms内准确识别并隔离故障线路,而且具有较强的耐受过渡电阻能力.

基于改进结构的自激式直流空气断路器小电流开断能力提升方法

大容量自激式直流空气断路器(SE-DCCB)广泛应用于轨道交通电力系统中,其可以快速切断大等级短路电流。但是SE-DCCB分断几百安小电流时自激磁场较小,导致电弧燃弧时间较长甚至开断失败。该文通过耦合自激线圈磁场的改进磁流体动力学(MHD)模型,仿真得出双气流涡旋和弧根黏滞是SE-DCCB开断小电流失败的主要原因。为了提高SE-DCCB开断小电流的能力,对其结构进行改进,改进结构SE-DCCB采用安装导磁条的导磁板,并减小跑弧道转弯角半径,可以加快弧根运动速度、削弱小电流开断时的双气流涡旋和弧根黏滞现象,从而缩短燃弧时间。同时,改进结构SE-DCCB降低了电弧熄灭时刻灭弧室入口处的温度,能够减小电弧熄灭后重燃的概率,提升其开断小电流的性能。该研究揭示了SE-DCCB小电流难以开断的物理本质,可为轨道交通用空气断路器提供研发指导。

一种可选择中断的混合式直流断路器拓扑

传统的混合式直流断路器应对瞬时性故障时必须先切断故障电流,再进行重合闸,会造成短暂性的电能供应中断。对此,提出一种适用于中压直流的可选择中断混合式直流断路器拓扑。该断路器可根据不同的故障类型选择运行方式,在与主导通支路串联的桥式结构中增加电容和限流电感抑制故障的电流上升,并储存能量,通过释能电阻对能量进行释放。对所提出的拓扑进行工作过程和理论分析。在单端直流等效系统中进行仿真验证,该结构在应对永久性短路故障时,可在9 ms内切除故障;应对瞬时性故障时,可使系统在不中断电流的情况下恢复正常运行,并释放故障时产生的能量。仿真结果验证了该拓扑的优越性。

计及柔性限流装置与直流断路器协同动作的电弧抑制暂态特性研究

直流系统的故障隔离是保证直流系统稳定运行的重要技术。针对传统故障隔离策略对直流断路器(direct current circuit breaker, DCCB)的性能要求较高的问题,提出了一种利用柔性限流装置(flexible current limiting device,FCLD)与DCCB协同动作的故障隔离策略。首先,研究了直流系统永久性故障和瞬时性故障情况下FCLD与DCCB的协同作用机理。其次,分析考虑FCLD电流抑制作用下DCCB开断过程的电弧暂态特性。最后,在Matlab/Simulink平台中进行仿真,验证所提协同策略的可行性。结果表明:FCLD可有效抑制DCCB的开断电弧;基于所提故障隔离策略,直流系统可在瞬时故障情况下实现平稳穿越,永久故障情况下实现DCCB的无弧开断。该策略降低了直流系统故障隔离过程中对DCCB的开断要求,提升了直流系统的故障穿越能力。

MMC-HVDC双极故障条件下自适应限流控制策略

直流断路器(direct current circuit breaker,DCCB)广泛应用于柔直输电系统,其造价与开断电流密切相关。文中从减小断路器开断电流的角度出发,设计适用于半桥型模块化多电平换流器(modular multilevel converter,MMC)的自适应限流控制结构。在分析MMC直流侧短路电流特性的基础上,利用换流站输入阻抗幅值的变化反映其故障深度,定义换流站故障深度系数K f;将K f引入MMC控制结构,使其与桥臂电压参考值关联,提出针对MMC直流侧短路故障的自适应限流控制方法;在PSCAD/EMTDC平台搭建半桥型MMC柔直输电系统模型,模拟直流侧短路故障清除过程,验证限流控制的有效性。仿真结果表明:文中提出的限流控制方法可依据MMC不同故障深度,实现差异化限流控制,减小DCCB开断电流,提升故障清除速度。

新型船舶中压直流固态断路器拓扑分析与设计

为解决船舶中压直流(medium voltage direct current,MVDC)电力系统直流电流开断困难,以及发生短路时故障电流上升率高且峰值大的问题,提出一种基于耦合电抗器的阻容限流型固态直流断路器拓扑。以晶闸管(silicon controlled rectifier,SCR)作为主开断器件,通过耦合电抗器来辅助晶闸管开断,并在直流系统发生故障时,通过换流过程将阻容限流元件接入,有效限制故障电流上升率和峰值,减少故障开断所需时间。基于所提拓扑设计了6 kV/4.2 kA的直流断路器模型,在PSCAD/EMTDC中进行仿真,并与现有拓扑进行对比分析。仿真结果表明:所设计断路器可针对直流系统不同的运行状态,按照不同的控制策略顺利完成对直流电流的开断,并且在开断速度、限流能力和金属氧化物避雷器(metal oxide arrester,MOA)耗能方面均具有一定优势。

Modular Reciprocating HVDC Circuit Breaker with Current-limiting and Bi-directional Series-parallel Branch Switching Capability

The high-voltage direct current(HVDC)circuit breaker is becoming popular with the rapid development of the flexible HVDC grid for efficient DC fault ride-through purposes.This paper proposes a novel module for reciprocating HVDC circuit breaker topology,whose branch connections are able to switch between series and parallel modes to limit the rising rate and interrupt the DC fault currents.Diode-bridge submodules(DBSMs)are used to compose the main branch for current interruption.Besides fault clearance,the proposed topology has the advantageous function of DC fault current limiting by employing DBSMs with bi-directional conduction capability.The topology can easily switch among branch connection modes through the assembled trans-valves,and their resistance and reactance are very small in the normal state when branches are in parallel and the values become promptly large in the transient state when the branches are series connected.With the modular design,it is easy to change the number of branches or sub-modules and the types of sub-modules to adapt to more specific needs.A 6-terminal modular multi-level converter(MMC)based HVDC grid is established in PSCAD/EMTDC,and various simulation scenarios are carried out to validate the proposed topology.

考虑MMC主动限流控制影响的直流断路器参数优化方法

直流断路器(DC circuit breaker,DCCB)成本是制约高压柔性直流系统发展的重要因素之一。为降低直流系统对断路器的要求,文中首先介绍模块化多电平换流器(modular multilevel converter,MMC)主动限流控制策略,提出状态空间平均模型下的直流短路电流时域解,分析采用主动控制方案改变电容放电状态占空比优化DCCB参数的可行性。提出考虑MMC主动限流控制的混合式DCCB参数的计算方法,分析占空比对DCCB的最大关断电流、机械开关时间、金属氧化物避雷器(metaloxide surge arrester,MOA)吸收能量的影响,设计DCCB的选型优化流程,降低DCCB的成本。最后,通过仿真和实验验证理论分析的合理性。

一种基于电容可控振荡换流的新型直流断路器

直流输配电网在远距离大容量电能传输、大规模新能源并网和源–网–荷协调控制等领域发挥重要作用。直流断路器(DC circuit breaker,DCCB)作为直流系统实现故障隔离的核心装备,目前还面临开断能力受限、成本高昂等问题,制约其在直流输配电系统中的广泛应用。该文首先提出一种新型电容可控振荡换流原理与拓扑电路,其通过激发电容振荡升压以实现振荡电流的快速提升,从而实现电流的转移与开断;然后对电容振荡换流机理进行数学分析,阐述所提直流断路器(DC circuit breaker,DCCB)拓扑构成与基本原理,并给出核心参数理论设计约束边界。最后,仿真分析20k V/3ms/15k A DCCB技术性能,论证所提拓扑的可行性与技术特点。研究结果表明,所提拓扑损耗低,可快速实现双向短路电流开断,与混合式DCCB相比,所提拓扑全控器件使用数量少、应力小,整体技术经济性能优异,具备良好的应用前景。

一种含卸能电阻的直流断路器的参数设计及性能分析

为了防止柔性直流输电系统在双极短路故障下过大的短路电流损坏输电系统,且考虑到过大的短路电流也会损坏断路器的避雷器,文中提出了一种可开断故障电流且有效减小避雷器吸能的直流断路器。利用PSCAD搭建了含卸能电阻的直流断路器模型和三端±350 kV柔性直流输电系统模型。在双极短路故障下,通过仿真对比分析了此模型与理想直流断路器模型和不含卸能电阻的直流断路器模型的区别。文中发现,含卸能电阻的直流断路器与理想直流断路器相比更容易切断故障电流,与不含卸能电阻的直流断路器相比有效减小了避雷器吸能。并且,通过仿真分析了使用不同参数的直流断路器的系统直流侧电流、电压波形,从而优化含卸能电阻的直流断路器的参数。

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.

6英寸8 kA/6.5 kV IGCT器件特性研究

集成门极换流晶闸管(IGCT)具有电压等级高、电流关断能力大和通态损耗低等优势,在电网领域的应用越来越广泛。为了进一步提升器件的关断能力,IGCT器件尺寸扩展至6英寸,在此介绍了6英寸8 kA/6.5 kV非对称IGCT器件的研制,通过优化阴极梳条排布和管壳设计,将IGCT元件寄生电感降到2 nH以下,降低了40%。通过优化N基区的选型,器件具备了稳健的4 kV直流阻断能力和8 kA的关断能力,并在高温8 kA下通态电压低于2.8 V,最后在直流断路器拓扑中进行了应用,这为研究更大功率等级的IGCT器件奠定了基础。

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SiC JFETs并联二极管桥式双向直流断路器

这里提出了一种基于碳化硅(SiC)结型场效应管(JFETs)并联的二极管桥式双向直流固态断路器。首先介绍了断路器的基本拓扑结构,分析了断路器动静态过程中并联均流影响因素,进而提出了具体的并联均流措施;并且分析了二极管桥在关断过程中对故障电流流通路径的影响,针对故障电流缓冲电路加装在二极管桥内外的不同情况进行仿真分析,从而获得缓冲电路的最佳安装位置。最终设计了断路器样机并进行实验验证,实验结果表明,所提断路器具有较好的并联均流效果,而且拥有良好的故障电流缓冲效果。

混合式高压直流断路器关键技术研究

高压直流断路器(Direct Current Circuit Breaker,DCCB)需承载直流线路正常工作时的工作电流,且需在规定时间内接通分断直流线路正常工作时的电流,以及分断直流线路短路故障电流。高压DCCB是确保高压直流输配电网安全、可靠运行的基础。混合式高压DCCB既具备机械式高压DCCB的优点,也具备固态高压DCCB的优点。在分析了各类混合式高压DCCB的拓扑、工作原理基础上,总结了混合式高压DCCB的设计关键技术,如电弧数学模型、串联均压、并联均流等问题。

大连轨道交通3号线直流断路器跳闸故障分析及其处理方法

大连轨道交通3号线列车运行过程中,发生过3次DC 1 500 V直流牵引供电系统直流断路器跳闸故障,影响列车正常运营。介绍直流牵引供电系统,以2020年12月30日发生的金家街站牵引变电所直流断路器MC01和MC04,以及香炉礁站牵引变电所直流断路器MC03和MC06故障跳闸后自动重合闸为例,分析故障现象,寻找故障原因,提出调整电流增量保护整定值的处理方法并验证。通过设计校核和实际运行结果发现,调整直流断路器电流增量保护整定值后,列车正常运营时,直流断路器电流增量保护未因列车牵引负荷增加而启动,表明调整电流增量保护整定值的处理方法是成功的。

柔性高压直流环网直流侧故障保护策略研究

直流故障保护问题是当前高压直流电网发展过程中所面临的关键技术问题之一。针对直流断路器在应用于高压直流电网故障保护时,可能面临直流故障发展迅速且有时难以区分的问题,该文研究了基于直流断路器附加电感的直流电网故障保护策略及其附加电感值的选取方法。通过对四端直流环网的直流极间短路故障特性进行分析,提出了由附加电感电压和模块化多电平换流器直流侧电压组合而成的直流断路器动作判据。由于该判据中所涉及参数都由本地测量实现,它具有不依赖于异地信号实时通信的特点。通过在Matlab/Simulink仿真平台上建立的四端直流环网模型所进行的仿真分析表明:该故障保护策略可以"有选择"地准确隔离故障线路或母线,并保证非故障部分在故障扰动后维持正常运行工况,且其不受故障位置、功率反转、控制方式和短路电阻的影响,并在不同结构的直流电网中具有较好的通用性。