MEASUREMENT OF ANODIC OVERVOLTAGE BY AMODIFIED CURRENT INTERRUPTION METHOD IN CRYOLITE-ALUMINA MELTS

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On-line Measurement for Ohmic Resistance in Direct Methanol Fuel Cell by Current Interruption Method

Electrochemical impedance spectroscopy (EIS) is widely used in fuel cell impedance analysis. However, for ohmic resistance (R Ω), EIS has some disadvantages such as long test period and complex data analysis with equivalent circuits. Therefore, the current interruption method is explored to measure the value of RΩ in direct methanol fuel cells (DMFC) at different temperatures and current densities. It is found that RΩ decreases as temperature increase, and decreases initially and then increases as current density increases. These results are consistent with those measured by the EIS technique. In most cases, the ohmic resistances with current interruption (R iR ) are larger than those with EIS (R EIS ), but the difference is small, in the range from –0.848% to 5.337%. The errors of R iR at high current densities are less than those of R EIS . Our results show that the R iR data are reliable and easy to obtain in the measurement of ohmic resistance in DMFC.

Direct Current Interruption with RLC Circuit-convoluted Arc Interaction

Investigations are reported into the use of an electromagnetically convoluted arc,external to a magnetic field(B-field)producing coil,in combination with a parallel R,L,C resonant circuit for interrupting quasi-steady currents.In order to elucidate the complex interactions between the arc,B-field and R,L,C circuit,the B-field producing coil is energised independently from the current to be interrupted and the R,L,C circuit.Experimental results are presented for the time variation of the currents flowing through the arc gap,the B-field coil and the parallel R,L,C circuit,along with the voltage across the arc gap.An insight is gained into the role of various effects,which are produced by the complex interactions and which might be used to advantage for direct current interruption.

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.

Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

直流快速开断技术研究进展和展望

由于直流电流无自然过零点且短路电流上升率高,直流电流快速开断与系统故障切除成为制约直流电力系统发展的一大瓶颈。该综述首先介绍了直流快速开断技术要求与难点。其次,详细分析了直流快速开断过程涉及的关键技术,包括电流转移技术、固态式直流开断技术、介质恢复技术和高速机械开关技术等,综述了各种技术的当前发展现状及其应用情况,对比了不同技术方案的特点及适应性。最后,对直流快速开断技术未来发展方向进行了讨论和总结,为小型化、高性能、低成本、高可靠快速直流断路器的研发及推广应用提供了新的技术思路。

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。

大电流空气电弧栅片烧蚀数值模拟与分析

电网输配电容量不断增加对低压断路器的开断性能提出了更高的要求。低压断路器开断大电流时,电弧烧蚀灭弧栅片产生的金属蒸汽会极大的影响断路器开断性能,阻碍断路器发展并且不利于电网安全运行。因此,建立了开断电流为10 kA的栅片烧蚀模型,研究了栅片烧蚀特性。模型考虑了栅片阴极端和阳极端不同的电弧能量注入,栅片材料的熔化、蒸发以及栅片表面形貌变化,并将弧根运动引入模型中。利用此模型计算了铁栅片烧蚀质量以及温度和熔化材料分布。仿真结果表明:栅片阴极端温升大小和范围均小于栅片阳极端的值。栅片表面熔化区域尺寸和位置随着弧根的移动而改变。栅片阳极端熔沸点来临时刻分别是2.19 ms和2.89 ms,烧蚀质量为1.84 mg。而栅片阴极端熔点来临时刻为4.12 ms,温度始终低于栅片材料沸点,烧蚀质量近乎为0。该文得到了单次开断下栅片两端烧蚀形貌,为研究多次开断下栅片烧蚀引起的栅片间短弧长度和移动路径变化对断路器开断性能的影响献力。

Characteristics of Bi-2223 HTS Tapes Under Short-Circuit Current Impacts in Hybrid Energy Transmission Pipelines

A hybrid energy transmission pipeline is proposed with the aim of long-distance cooperative transmission of electricity and chemical fuels, which is composed of an inner high-temperature superconducting (HTS) power cable and outer liquefied natural gas (LNG) pipeline. The flowing LNG could maintain the operating temperature of the inner HTS power cable within the range of 85 K-90 K, thus the Bi-2223 superconductors in the HTS power cable produce little Joule loss with the transmission current below the critical current. Owing to the advantages of high power density, low transmission losses and economical manufacturing costs, the hybrid energy transmission pipeline is expected to be widely utilized in the near future. In order to ensure the safety of the HTS power cable and explosive LNG in case of short-circuit faults, this paper tests and analyzes the characteristics of Bi-2223 HTS tapes of the Type HT-CA, Type HT-SS and Type H models under short-circuit current impacts at the LNG cooling temperature (85 K-90 K). An experimental platform is designed and established for the ampacity tests of HTS tapes above LN2 cooling temperature (77 K). The AC over-current impact tests at 85 K-90 K are carried out on each sample of Bi-2223 tapes respectively, and the experimental results are analyzed and compared to evaluate their performances under different operating conditions. The results indicate that the Type HT-CA tape can withstand 50 Hz short-circuit current impact with the amplitude of 1108 A (10 times of critical current Ic ) for 100 ms at 90 K, and its resistance is the smallest of the three tested samples under similar current impacts. Therefore, the Type HT-CA Bi-2223 tape is the optimal superconductor of the HTS power cable in the hybrid energy transmission pipeline.

Interruption Characteristics of High-speed Switches in 500 kV Fault Current Limiter with High Coupled Split Reactance

A 500 kV high-voltage AC fault current limiter(FCL)based on a high coupled split reactor(HCSR)is pro-posed by the National key R&D project team.Low impedance under normal conditions and high impedance under short-circuit conditions are accomplished by the cooperation of HCSR and high-speed switches.High-speed switches play an important role in current limiting processes,thus interruption characteristics of the high-speed switch in the 500 kV FCL are studied in this paper.The simulation model of the FCL and the external equivalent power grid are established.The short-circuit current and recovery voltage characteristics of the high-speed switch in FCL are simulated.The results show that maximum DC component of the short-circuit current of the high-speed switch reaches 91%,the maximum peak value is 118 kA,and the longest arcing time is 14.8 ms.There is a discontinuity in the curve of the short-circuit current peak and arcing time as a function of the short-circuit occurrence time;the peak recovery voltage of a single break of the high-speed switch has a maximum value of 87.5 kV under a three-phase ungrounded short-circuit condition,and the rate of rise of recovery voltage is o.22 kV/s.The recovery voltage peak shows a period change with the short-circuit occurrence time,and the period is 10 ms.The effects of the shunt capacitor value and short-circuit ground resistance on the recovery voltage of high-speed switching are also studied.The research can be used for reference by R&D personnel and testersof500kVFCLs.Index Terms-Fault current limiter(FCL),high coupled split reactor(HCSR),high-speed switch,interruption characteristics,short circuit current.

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.

Placement optimization of Multi-Type fault current limiters based on genetic algorithm

The fault current limiter(FCL)is an effective measure for improving system stability and suppressing short-circuit fault current.Because of space and economic costs,the optimum placement of FCLs is vital in industrial applications.In this study,two objectives with the same dimensional measurement unit,namely,the total capital investment cost of FCLs and circuit breaker loss related to short-circuit currents,are considered.The circuit breaker loss model is developed based on the attenuation rule of the circuit breaker service life.The circuit breaker loss is used to quantify the current-limiting effect to avoid the problem of weight selection in a multi-objective problem.The IEEE 10-generator 39-bus system in New England is used to evaluate the performance of the proposed genetic algorithm(GA)method.Comparative and sensitivity analyses are performed.The results of the optimized plan are validated through simulations,indicating the significant potential of the GA for such optimization.

Research on Numerical Simulation of 3D Leakage Magnetic Field and Short-circuit Impedance of Axial Dual-low-voltage Split-winding Transformer

It is difficult to accurately calculate the short-circuit impedance, due to the complexity of axial dual-low-voltage split-winding transformer winding structure. In this paper, firstly, the leakage magnetic field and short-circuit impedance model of axial dual-low-voltage split-winding transformer is established, and then the 2D and 3D leakage magnetic field are analyzed. Secondly, the short-circuit impedance and split parallel branch current distribution in different working conditions are calculated, which is based on field-circuit coupled method. At last, effectiveness and feasibility of the proposed model is verified by comparison between experiment, analysis and simulation. The results showed that the 3D analysis method is a better approach to calculate the short-circuit impedance, since its analytical value is more closer to the experimental value compared with the 2D analysis results, the finite element method calculation error is less than 2%, while the leakage flux method maximum error is 7.2%.

真空灭弧室温升特性仿真分析

研究真空灭弧室的温升特性对于其结构参数的优化和保障其自身的流通能力具有重要意义。用SolidWorks软件建立真空灭弧室的导电回路3D模型并对其结构进行简化,采用ANSYS Workbench软件对真空灭弧室的仿真模型进行涡流场-温度场耦合分析,对额定电流状态下导电回路的温升进行仿真计算。结果表明:增大触头片接触点直径、增大杯壁厚度、减小杯壁螺旋开槽长度和增大导电杆的半径等尺寸参数对真空灭弧室的温升均有所改善。对优化后的模型按照触头材料为CuCr50和CuCr10分别对其进行仿真,结果发现,CuCr10的触头片材料温升远低于CuCr50时的温升,且CuCr10能承受更大的电流,因此可以考虑通过改变触头材料来实现优化真空灭弧室的温升特性。

一种基于IGCT的地面自动过分相方案及其电压切换控制策略研究

针对传统基于晶闸管的地面自动过分相系统中电力机车仍存在毫秒级的失电时间且可能面临励磁涌流的问题,提出一种基于集成门极换流晶闸管(integrated gate-commutated thyristor,IGCT)的地面自动过分相方案,采用IGCT取代晶闸管阀组进行中性区电压切换,实现开关开通和关断时间的完全可控。进一步基于磁链分析,以中性区电压切换后电力机车主变压器不产生磁偏为控制目标提出不同供电臂相位差情况下基于IGCT的地面自动过分相方案的电压切换控制策略,并搭接仿真模型对其工作效果进行验证。仿真结果表明,所提方案可以将列车的失电时间进一步缩短至几百微秒且有效避免电力机车主变压器的励磁涌流,减小电分相对列车运行的影响。

一种阻容型限流式混合直流断路器拓扑结构研究

针对轨道交通直流牵引供电系统故障短路电流大、上升速率快等问题,文中提出1800V阻容型限流式混合直流断路器拓扑结构,分析了工作原理和整机开断过程,确定了整机开断限流参数取值。采用MATLAB/Simulink建立阻容型限流式混合直流断路器模型,对比分析阻容限流拓扑结构与传统电感限流拓扑结构对开断故障短路电流峰值和整机开断时间的影响,阻容限流拓扑结构效果更优。搭建整机开断试验平台,进行小电流开断试验验证,试验结果表明与传统电感限流拓扑结构相比,阻容限流拓扑结构有效降低故障电流幅值30%以上,缩短整机开断时间10%以上,与仿真结果基本一致。文中为限流式混合直流断路器样机研制提供一定的参考。

儿童阻塞性睡眠呼吸暂停低通气综合征治疗的研究进展

儿童阻塞性睡眠呼吸暂停低通气综合征(OSAHS)是儿科一种常见的疾病,其特征是儿童在睡眠过程中频繁发生完全或不完全的上气道阻塞,扰乱儿童正常通气和睡眠结构而引起睡眠中断、低氧血症、高碳酸血症等睡眠障碍。儿童OSAHS是一种异质性和动态的疾病,涉及多学科,具有多种治疗方案。本文回顾了儿童OSAHS治疗方案及其适应证的科学进展,介绍该病的治疗和研究现状。

关合电容器组高频涌流对真空灭弧室绝缘特性的影响研究

研究发现单断口或者常规串联双断口真空断路器,无法有效提高电容器组开断参数、降低重击穿概率的原因为无法避免高频涌流电弧对触头表面的烧蚀破坏,从而导致断口绝缘强度大为降低。研究获得了高频涌流电弧烧蚀对真空断口绝缘强度和串联断口分压特性的影响规律;高频涌流电弧烧蚀对单个真空灭弧室和串联双真空断口绝缘强度的影响规律及串联断口的分压规律。实验结果表明,真空灭弧室受到涌流电弧烧蚀后场致发射电流大大增加,触头表面破坏越严重场致发射电流越大。触头都受到烧蚀后的串联双断口各自分压约50%,而未受烧蚀灭弧室与受烧蚀灭弧室的串联双断口,前者分压大于70%。以上研究成果可为提高断口绝缘强度、提升断路器电容器组开断参数及降低重击穿概率提供理论参考。

脉冲电压老炼过程中真空击穿机制演化机理

脉冲电压老炼是提高真空电极间隙击穿特性的有效方法。该文采用64/700μs冲击电压对纯铜球电极进行脉冲电压老炼试验,利用X射线光子能谱表面分析、阴极表面粗糙度及扫描电子显微镜测量,结合Fowler-Nordheim理论,分析诊断了脉冲电压老炼过程中真空击穿波形的击穿机制,并揭示真空击穿机制的演化机理。结果表明:阴极表面X射线能谱Cu峰变化对比,表面粗糙度及其突起结构和微观金属微粒分别支撑验证了老炼过程中击穿波形包含脉冲电流诱发真空击穿,场致发射诱发真空击穿和微粒诱发真空击穿3种击穿机制。脉冲电压老炼过程中存在不同真空击穿机制的演化过程,具体为:老炼起始阶段的击穿机制主要为脉冲电流诱发真空击穿和微粒诱发真空击穿;随后老炼过程由微粒诱发真空击穿主导,脉冲电流诱发真空击穿消失,场致发射诱发真空击穿逐渐增多;最终,老炼饱和阶段由场致发射诱发真空击穿与微粒诱发真空击穿共同主导。该试验结果为从击穿机制演化机理角度提升真空电极间隙击穿特性提供重要理论参考。

执行时效排除规则的困境及其破解

《民事诉讼法》第261条“债权人发现被执行人有其他财产的,可以随时请求人民法院执行”一直被解释为申请执行期间适用的排除规则,并得到《民诉法解释》第515条和第517条“终结本次执行程序”规则的确认,但其实该解释与2007年后申请执行期间的“时效”转向相冲突。《强制执行法(草案)》第83条将“自终结本次执行程序之日起满五年且未发现被执行人可供执行的财产”作为执行终结事由之一,虽有否定执行时效排除规则的意味,但它一方面使得申请执行期间走回“期限”定性的老路,另一方面有苛责权利人之嫌。《民事诉讼法》第261条中“可以随时请求人民法院执行”是对“申请执行权不消灭”的操作性强调,也是对“债权未消灭”的程序性回应,与执行时效无关。终本程序的执行时效后果应直接适用《民法典》第195条“时效中断”规则,产生“从有关程序终结时起,时效期间重新计算”的效果。