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.

The Voltage Distribution Characteristics of a Hybrid Circuit Breaker During High Current Interruption

Hybrid circuit breaker （HCB） technology based on a vacuum interrupter and a SF6 interrupter in series has become a new research direction because of the low-carbon requirements for high voltage switches. The vacuum interrupter has an excellent ability to deal with the steep rising part of the transient recovery voltage （TRV）, while the SF6 interrupter can withstand the peak part of the voltage easily. An HCB can take advantage of the interrupters in the current interruption process. In this study, an HCB model based on the vacuum ion diffusion equations, ion density equation, and modified Cassie-Mayr arc equation is explored. A simulation platform is constructed by using a set of software called the alternative transient program （ATP）. An HCB prototype is also designed, and the short circuit current is interrupted by the HCB under different action sequences of contacts. The voltage distribution of the HCB is analyzed through simulations and tests. The results demonstrate that if the vacuum interrupter withstands the initial TRV and interrupts the post-arc current first, then the recovery speed of the dielectric strength of the SF6 interrupter will be fast. The voltage distribution between two interrupters is determined by their post-arc resistance, which happens after current-zero, and subsequently, it is determined by the capacitive impedance after the post-arc current decays to zero.

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。

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.

基于单端高频电流量的MMC-MTDC输电线路保护方案

为克服传统高压直流输电线路保护利用单端电气量无法可靠区分区内、外故障的缺陷,提出一种通过广义S变换提取直流线路故障电流高频频带幅值特征的单端量保护新方法。该方法在配备有混合直流断路器的直流线路发生故障时,利用1000~2500 Hz各采样频率电流横差值在区外明显小于区内的特征,构造了区内、外故障判据。利用300~1000 Hz的特征频率在单极接地故障时故障极特征频率电流幅值比非故障极大,以及两极短路故障时两极的特征频率电流幅值近似相等的特征,构造了故障启动判据和选极判据。在RTDS仿真平台搭建了风光储联合发电站经高压直流外送的三端柔性直流输电系统模型。仿真结果表明,所提方法能快速、可靠地识别故障类型和故障范围。同时,仿真验证了基于混合直流断路器的直流故障穿越方案的有效性。

基于IDCB-MMC的混合直流输电系统

提出了一种由集成直流断路器的模块化多电平换流器(modular multilevel converter integrated with DC circuit breaker,IDCB-MMC)和晶闸管换流器组成的混合直流输电系统。在发生直流短路故障时,通过换流器与直流断路器在控制上的配合,IDCB-MMC可以将故障电流的能量转移到并联于直流母线间的能量吸收支路中,从而可以避免使用成本高且占地大的电力电子开关支路。晶闸管换流器则可以通过快速转换到逆变状态实现直流故障电流的清除。对1 000 MW/±320 kV的双端混合直流输电系统中的一极进行了仿真研究。仿真结果表明IDCB-MMC可以有效清除直流短路故障电流,实现系统的自动恢复,结果也验证了由IDCB-MMC与晶闸管换流器组成的混合直流输电系统的可行性。

A Hybrid Circuit Breaker Based on Current Commutation Approach for Multi-feeder DC Railway Substations

The paper presents an economic hybrid circuit breaker for limiting and interrupting the faults in DC railways substations. For fast fault current interruption, the hybrid breaker incorporates high speed mechanical contacts actuated by power semiconductor devices. Additionally, to avoid formation of electric arc, a commutation circuit is used to inject a counter current during fault interruption. In a real railway substation, each feeder is connected to the main DC bus through an expensive air magnetic DC circuit breaker and to an auxiliary DC bus through another expensive breaker. This leads to high cost especially in railway substation with multi feeders which are used to energize the vehicle transmission lines. In this paper, all DC breakers in DC railway substations are replaced by the suggested circuit breaker, which consists of a high speed mechanical contact with two semiconductor devices in each feeder and only one commutation circuit for injecting the counter current in all faulted feeders. The fault diagnosis is designed to detect the abnormal condition (current or voltage) in all feeders and direct the injected current from the commutation circuit to the faulted feeder only when the abnormal reaches a predetermine level. The suggested breaker is able to detect and interrupt any cascading of faults.

Low-loss and Compact Hybrid DC Circuit Breaker Scheme Using Self-commutated Semiconductor Switch Module

In traditional hybrid DC circuit breakers(HCBs)schemes,complex equipment is usually required to ensure current commutation from mechanical to semiconductor switches,which cause not only additional construction costs and volume but also additional losses and maintenance work.Different from this condition,a low-loss and compact HCB scheme that does not use separate current commutation equipment is proposed in this study.By rationally using the charge and discharge of the snubber capacitor,the self-commutated semiconductor switch(SCS)module can integrate both the current commutation and shutdown functions,thereby greatly reducing cost and volume.The working process is discussed and analyzed in detail,and then a 10-kA prototype is developed and tested,which verifies the feasibility and effectiveness of the proposed scheme.Index Terms-HVDC circuit breakers,hybrid DC circuit breakers(HCBs),self-commutated semiconductor switch(SCS).

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.

具备自适应重合闸能力的多端口混合式直流断路器

为解决柔性直流电网中混合式直流断路器成本高以及盲目重合闸的问题,提出了一种具备自适应重合闸能力的多端口混合式直流断路器。所提断路器能够在能量耗散期间旁路故障线路中的限流电抗器,配合电容充电回路的导通,将本应经避雷器耗散的限流电抗器能量转移到电容中,从而有效减少了故障隔离时间与避雷器能量耗散压力,并为故障性质的判别提供了能量支持。同时,该断路器通过共享主断路器的方式实现故障隔离,结合避雷器泄能需求的下降,大大降低了断路器的制造成本,在经济性方面优势明显。此外,该断路器利用故障识别电流与电容电压在永久性故障与瞬时性故障下的幅值差异来识别故障性质,实现了自适应重合闸,操作简单且易于控制。最后,利用PSCAD/EMTDC在三端MMC柔性直流系统环境下对所提方案的有效性进行了仿真验证,并通过与其他方案的对比分析,证明了所提方案的优越性。

基于电容自然充电换相的混合式直流断路器设计与仿真

以晶闸管作为主断器件是降低混合式直流断路器造价和技术难度的手段之一,电容电压是此类直流断路器能够顺利开断直流故障的关键影响因素。现有结构中电容大多为预充电型,但预充电方式和电容电压的维持较为复杂。因此,该文提出一种基于电容自然充电换相的混合式直流断路器,利用母线电压与预充电电容的电压差值实现电容的预充电和电容电压的自动维持,从而保证断路器的开断能力。此外该断路器还具备二次开断能力,可以满足极短时间内重复开断的需求。针对所提断路器的工作过程和元器件参数进行了详细的理论推导,基于PSCAD/EMTDC建立单端等效和四端柔性直流电网模型验证了所提结构的适用性。最后与其他方案进行比较,结果表明,所提方案在开断速度、电容预充电方式和二次开断方面具备一定优势。

一种双电容换流型混合式直流断路器

混合式直流断路器可以快速、准确隔离线路故障,在直流电网故障清除难题中发挥重要作用。为解决直流断路器开断能力要求高、限流能力弱、制造成本大、故障隔离速度慢等问题,提出一种双电容换流型混合式直流断路器(Double capacitor commutated hybrid DC circuit breaker,D-C-DCCB)拓扑。构建断路器时,巧妙利用自充电通路实现电容预充电及反向充电后电容能量的耗散。通过电容反向充电与阻感限流支路降低故障电流上升速率及峰值,利用限流电阻与二极管组实现限流电感,完成限流工作后被短路及储存能量耗散,加快故障隔离速度的同时,有效减少了避雷器吸收能量。对所提断路器的拓扑结构及工作原理进行分析及推导,在PSCAD/EMTDC中对所提断路器拓扑进行了四端直流电网仿真验证,与现有的直流电网故障清除拓扑在性能及经济性方面进行了对比,证明了所提断路器具有性能好、经济性高的优点。

一种基于电容主动钳位式混合式直流断路器

混合式直流断路器兼具机械式直流断路器的静态特性与固态直流断路器的动态特性,具有较快的开断速度和较低的通态损耗,是应用于中高压直流输配电系统的优选技术方案。然而,基于模块级联的混合式直流断路器存在投资成本较高、避雷器吸能较高、不具备故障性质判别能力等问题,限制了断路器的工程化应用。该文在现有结构的基础上进行一定的改进,提出一种基于电容主动钳位式混合式直流断路器。主要利用电容电压钳位换流站侧电压,避免了换流站电压迅速跌落的同时降低了换流站侧的故障电流峰值。此外,电容电压还可作为线路故障和重合闸时的辅助判据。针对所提结构进行了详细的理论推导和分析,在PSCAD/EMTDC中建立四端直流环网对所提结构进行验证,并与原有方案进行对比。仿真结果证明所提结构可行且相对原有方案具备一定优势。

真空与气体一体化串联机械开关及其直流快速转移应用

为提升中压混合式直流断路器的自然换流性能,该文提出一种真空与气体一体化串联机械开关,分析真空与气体一体化串联用于电流转移性能的工作原理。并基于此设计了双超程联动的真空与气体一体化串联开关实验样机,研究了气体类型、气压、触头结构、触头材料等参数对电弧电压特性的影响规律,确定了W70Cu桥式两触点结构,采用H2和N2体积比为2:3、气压为0.3 MPa的氢氮混合气体,弧压可由20 V提升到120 V,电流转移时间由1 900μs缩短至300μs。同时测试了静态瞬态开断电压(TIV)分布特性,真空间隙承担主要电压(55%),串联整机耐压水平为20 kV。验证了真空与气体一体化串联开关应用于中压混合式直流断路器的可行性和有效性。

混合式直流断路器状态感知技术与智慧框架体系探讨

直流断路器是柔性直流输电工程中故障清除和隔离的关键设备,当前的热点集中在新型拓扑结构、直流开断特性和新型电力电子器件等功能方面的研究,对其全状态的智能感知和状态评估方面研究较少。该文以混合式直流断路器为研究对象,全面梳理了需要重点监测的状态量,归纳了混合式直流断路器中快速机械开关、压接式绝缘栅双极性晶体管(insulated gate bipolar transistor,IGBT)、避雷器、快速机构动作电容和隔离供能单元等关键组件状态量的感知方法。基于现有研究,提出了智慧型直流断路器的框架体系。分析了所提框架体系中智能感知层、信息通信层、数据融合层和智能应用层的实现思路,为实现直流断路器的智能化和模块化提供一定参考依据。

自触型低压混合式直流断路器系统设计与开断特性研究

低压混合式直流断路器具有低功耗、高开断性能、选择性保护等优点,能更好地满足光伏和储能系统以及零碳建筑等应用需求。该文提出一种自触型低压混合式直流开关拓扑,首先通过对混合式断路器工作原理分析,建立基于电弧供能、驱动的机电系统耦合设计方法,该方法利用电弧能量为电子电路供能,并将电弧电压作为换流支路导通的控制信号,从而实现短路故障下系统的自动触发,并提出核心功能模块设计的理论依据。在此基础上,研制低压混合式断路器样机并验证设计方案的有效性,并对比分析不同因素对开断特性的影响规律。试验表明,相较于传统机械开关,小电流开断时间缩短85.4%、电弧能量减少94.1%,提升了断路器电气寿命,同时实现1.1 kA短路电流开断,发现系统总体响应时间与燃弧初期电压上升速率成正相关,电弧电导、支路寄生电感增大均会延长换流时间,电弧重燃概率则主要受外部系统参数影响。结果可为低压直流混合式断路器的优化设计和性能提升提供一定参考。

基于经验傅里叶分解的混合式高压直流断路器耗能支路故障检测方法研究

为实现更强的能量耗散能力,混合式高压直流断路器的耗能支路需串并联大量金属氧化物压敏电阻(metal oxidevaristor,MOV),耗能支路的可靠性将直接影响混合式高压直流断路器的可靠性。但是,现有的耗能支路故障检测方法并不能适应整个能量耗散阶段。为此,提出一种基于经验傅里叶分解的混合式高压直流断路器耗能支路故障检测方法,具体为:首先是信号预处理,对耗能支路每个子模块的分支电流进行归一化和一阶差分计算来获取分析电流;然后是故障特征提取,利用经验傅里叶分解(empirical Fourier decomposition,EFD)对分析电流进行分解,提取最高频时频分量作为故障特征分量;最后是检测判据,通过故障特征分量构造突变峰值量化指标,进而通过突变峰值实现耗能支路故障检测。大量实验表明,该检测方法可在能量耗散阶段末期实现可靠地故障检测,且具备一定的抗干扰能力。

基于光伏充电的低压混合式断路器设计及仿真

直流断路器是实现直流系统电流故障清除和隔离的关键设备。基于人工过零点的直流断路器熄弧时刻具有不确定性,且换流电容需要更换辅助电源,降低断路器可靠性,增加维护成本。为此,在传统直流断路器基础上,提出了一种基于光伏充电的混合式直流断路器拓扑结构设计方案。该方案在断路器过零点未熄弧时闭锁IGBT开关,加速电弧熄灭,并设计光伏储能供电系统为换流电容预充电能,以保障断路器持续运行。同时对所提断路器的拓扑结构、开断时序、拓扑参数进行了设计,基于MATLAB/Simulink实验平台建立了150 V混合式直流断路器模型,讨论IGBT开关器件闭锁时刻及电阻电容二极管(resistance-capacitance diode,RCD)缓冲电路对断路器开断的影响。在此基础上,通过仿真实验分析了正常和短路工况下断路器开断过程,验证了所提方案的可行性。

混合式直流断路器内部关键参数对电弧电流转移特性的影响研究

真空电弧电流转移是自然换流型混合式直流断路器开断过程中的一个重要组成部分。文中通过建立真空电弧电流转移的理论分析模型,得出影响真空电弧电流转移的主要因素为真空电弧电压、内部杂散电阻电感参数和电力电子器件的串并联结构。实验方面,通过改变电力电子开关中电力电子器件的串联或并联个数研究了电力电子器件的串并联结构对真空电弧电流转移特性的影响,通过改变电力电子开关中杂散电感或电阻的数值和所处位置研究了内部杂散电阻电感参数对真空电弧电流转移特性的影响。最后,探究了促进电弧电流转移的方法。本研究将为混合式直流断路器的结构设计和参数优化提供理论依据。