A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

Optimization of short-circuit transition parameters of Q235B steel GMAW based on orthogonal gray relational analysis

In gas metal arc welding(GMAW)process,the short-circuit transition was the most typical transition observed in molten metal droplets.This paper used orthogonal tests to explore the coupling effect law of welding process parameters on the quality of weld forming under short-circuit transition,the design of 3 factors and 3 levels of a total of 9 groups of orthogonal tests,welding current,welding voltage,welding speed as input parameters:effective area ratio,humps,actual linear power density,aspect ratio,Vickers hardness as output paramet-ers(response targets).Using range analysis and trend charts,we can visually depict the relationship between input parameters and a single output parameter,ultimately determining the optimal process parameters that impact the single output index.Then combined with gray the-ory to transform the three response targets into a single gray relational grade(GRG)for analysis,the optimal combination of the weld mor-phology parameters as follows:welding current 100 A,welding voltage 25 V,welding speed 30 cm/min.Finally,validation experiments were conducted,and the results showed that the error between the gray relational grade and the predicted value was 2.74%.It was observed that the effective area ratio of the response target significantly improved,validating the reliability of the orthogonal gray relational method.

Partitioning Calculation Method of Short-Circuit Current for High Proportion DG Access to Distribution Network

Aiming at the problemthat the traditional short-circuit current calculationmethod is not applicable to Distributed Generation(DG)accessing the distribution network,the paper proposes a short-circuit current partitioning calculation method considering the degree of voltage drop at the grid-connected point of DG.Firstly,the output characteristics of DG in the process of low voltage ride through are analyzed,and the equivalent output model of DG in the fault state is obtained.Secondly,by studying the network voltage distribution law after fault in distribution networks under different DG penetration rates,the degree of voltage drop at the grid-connected point of DG is used as a partition index to partition the distribution network.Then,iterative computation is performed within each partition,and data are transferred between partitions through split nodes to realize the fast partition calculation of short-circuit current for high proportion DG access to distribution network,which solves the problems of long iteration time and large calculation error of traditional short-circuit current.Finally,a 62-node real distribution network model containing a high proportion of DG access is constructed onMATLAB/Simulink,and the simulation verifies the effectiveness of the short-circuit current partitioning calculation method proposed in the paper,and its calculation speed is improved by 48.35%compared with the global iteration method.

Stability analysis of CO_(2)gas shielded welding short-circuit transition process based on GMAW dynamic model

Base on the arc phase and short-circuit phase and their relationship, the paper considers the changes of the extension of wire, the arc length, liquid bridge resistance and mass of liquid bridge, combines the improved “mass-spring” model with the loop model of welding power system, puts forward the critical judgment condition of droplet transition, and establishes a more accurate dynamic model for describing the short-circuit transition process. The dynamic changes of short-circuit transfer frequency, welding current and voltage, contact droplet and residual droplet equivalent radius and droplet equivalent radius at different wire feeding speeds were calculated and analyzed, and compared with the experimental results. It shows that the fluctuation of droplet displacement, velocity and wire extension length at the optimal arc starting point is the smallest. The smaller the initial liquid bridge curvature radius is, the better the stability of short-circuit transfer is.

Research on Inter-turn Short-circuit Fault Diagnosis Method Based on High Frequency Voltage Residual for PMSM

Inter-turn fault is a serious stator winding short-circuit fault of permanent magnet synchronous machine(PMSM). Once it occurs, it produces a huge short-circuit current that poses a great risk to the safe operation of PMSM. Thus, an inter-turn short-circuit fault(ITSCF) diagnosis method based on high frequency(HF) voltage residual is proposed in this paper with proper HF signal injection. First, the analytical models of PMSM after the ITSCF are deduced. Based on the model, the voltage residual at low frequency(LF) and HF can be obtained. It is revealed that the HF voltage residual has a stronger ITSCF detection capability compared to the LF voltage residual. To obtain optimal fault signature, a 3-phase symmetrical HF voltage is injected into the machine drive system, and the HF voltage residuals are extracted. The fault indicator is defined as the standard deviation of the 3-phase HF voltage residuals. The effectiveness of the proposed ITSCF diagnosis method is verified by experiments on a triple 3-phase PMSM. It is worth noting that no extra hardware equipment is required to implement the proposed method.

海上风电低频输电系统快速母线保护

海上风电低频输电系统母线故障后,换流器型电源等效电势与阻抗因控制的切换与调整过程,不再像传统电网可视为恒定。文中理论分析了母线电流差动保护适应性,明确故障控制策略对差动保护灵敏度的影响方式。利用母线区内外故障所对应的故障等效模型不同,提出基于时域全量模型识别的母线保护。该保护原理反映被保护元件自身拓扑的变化,理论上具有不受电源特性影响的优势,同样适用于其他换流器型电网。同时,所提保护在时域中实现,不存在相量提取问题,动作速度快。最后,在PSCAD/EMTDC中搭建了仿真模型,验证了所提母线保护的可靠性和快速性。

涂层传热性能对母线散热能力影响分析

为提升电力开关柜散热性能、提高供配电稳定性,本文依据传热学基础理论对电力开关柜传热过程进行分析,采用溶液共混法成功制备了适用于电力开关柜母线散热的涂层材料,并基于电磁-热-流多物理场耦合原理构建了电力开关柜涂层-热分析模型,结合母线负载电流计算理论,从涂层热导率、发射率等方面对涂覆散热涂层前后的电力开关柜传热特性进行分析。结果表明:涂层热导率相比于涂层发射率对母线温升影响较小,母线表面涂覆涂层之后,B相母线表面发射率由0.2增大到0.846时,三相母线最大负载电流与未涂覆相比提升18.75%。

基于有限时间观测器的光储系统母线电压互补滑模控制

针对光储直流微网混合储能系统易受能源间歇性输入、负载随机性扰动以及功率流向切换等干扰,会造成母线电压波动、系统功率失稳等问题,提出一种基于有限时间观测器的互补滑模控制(FTESO+CSMC)策略.首先,根据混合储能元件的高低频特性,对系统差额功率进行电流等效分配.然后,设计有限时间扩张状态观测器,对系统受到的总扰动进行观测,并将扰动观测值作为前馈项输入互补滑模控制器中,对系统扰动进行补偿,保证系统状态在有限时间内达到收敛,提高了系统的快速性和抗扰性,并根据Lyapunov理论证明了控制系统的稳定性.最后,基于MATLAB仿真平台,对多种模拟工况进行仿真,仿真结果表明,相较于传统控制策略,本文所提控制具有更快的响应速度以及更好的抗扰性能.

基于馈线和电流的专用轨回流牵引供电系统接地故障保护

对于专用轨回流牵引供电系统,负极回流轨对地具有良好的绝缘特性,极大地限制了正极接地故障所产生的短路电流。由于负极母线电位下降、接地电阻较大等原因,现有的正极接地保护在实际应用中暴露出选择性差、灵敏度低等问题。本文通过对专用轨回流牵引供电系统短路电流以及负荷电流的潮流分析,提出以供电区间馈线和电流作为正极接地故障判断的特征量,并设计基于该故障特征量的保护方案,基于MATLAB/Simulink仿真系统,验证了该保护方案的有效性。

并联电容器叠层母排寄生电感建模及测量方法

并联电容器母排的寄生电感是电力电子变换器换流回路总寄生电感的主要部分,寄生电感易导致电压过冲,因此需要精确提取和计算叠层母排的寄生电感。这里首先以一种5电容器并联的叠层母排为研究对象,建立了多电容器并联叠层母排的电感计算模型;在此基础上,提出一种可对母排寄生电感进行直接测量的实验方法,规避了在母排上连接电容器所产生的误差。最后,使用该方法对叠层母排寄生电感值进行实验测量,并将测量结果与有限元仿真计算结果进行对比,测量结果与仿真结果的偏差在2%以内,验证了所提方法的有效性和准确性,从而为叠层母排的低感设计提供了测量验证的基础方法。

基于磁流体稳定性提升的电解槽母线改造研究

磁场是电解槽磁流体稳定性的决定性因素,本文对铝电解槽的磁流体稳定性进行研究,通过采用自均衡网络化母线技术降低电解槽垂直磁场,改造后的垂直磁场平均降低47.5%,且四个象限磁场强度分布均匀。通过瞬态磁流体模型及流动场稳定性分析验证,500s左右后电解槽可自行恢复稳定状态,界面变形减小1.2cm,证明采用自均衡网络化母线技术后的电解槽自平衡能力及抗波动能力均得到增强,从而节省直流电耗150kWh/t-Al。

一起500kVGIL管母支柱绝缘子故障分析

为了分析某换流站的一起500 kV GIL管母支柱绝缘子故障,对故障GIL开展解体检查、结构原理分析、重力影响分析、导体膨胀仿真计算、绝缘子浇注工艺分析、绝缘子装配工艺分析等。通过研究分析,确定了GIL故障原因为三支柱绝缘子铝质金属表面与绝缘体之间存在微小间隙缺陷,在生产、运输、安装、运行等过程中小间隙逐渐扩展、劣化,最终导致击穿放电。最后从强化生产工艺控制、提升出厂检测标准、提高运输过程管控要求、加强现场超声波带电局放测试几方面提出改进建议,为后续GIL生产、运输、运维等方面提供借鉴。

备用电源与应急电源对比及供电方案探讨

对比多本国家标准及规范对备用电源和应急电源术语的定义;分析二者的区别和侧重点;提出供配电系统设计时应充分理解备用电源和应急电源的定义,根据工程的负荷性质、用电容量、工程特点、系统规模和发展规划及当地供电条件进行多方案比选,并对5种备用电源供电方案和3种应急电源供电方案的特点和适用范围进行探讨。

沿海核电厂输变电设备绝缘材料在台风产生盐害情况下绝缘降低发生闪络导致丧失厂外电有关现象的研究

2020年9月,韩国8台核电机组因台风“美莎克”(2020年9月3日)和“海神”(2020年9月7日)发生丧失厂外电源事件。发生此事件是由于核电厂与外部变电站及相关设施之间的输电线以及绝缘材料路出现问题。本文调查分析了丧失厂外电的原因和事故序列,判断事件主要原因为输变电设备绝缘材料在台风产生盐害情况下绝缘降低发生闪络导致丧失厂外电。同时,梳理了国内外类似盐害现象导致绝缘降低的事件,研究盐害引起绝缘降低发生的闪络现象,得出研究结论并提出合理改进建议。

考虑母线电压波动的光伏混合储能控制策略

混合储能是保障光伏系统稳定运行的重要技术之一。为保证光储系统稳定运行,提出了一种考虑母线电压波动的控制策略。通过将母线电压波动大小分解为正向和反向两种反馈,对混合储能系统中的超级电容电流内环参考电流进行调节,进而将母线电压波动相关的量作为控制信号对超级电容功率进行调整,最后在Simulink中搭建了仿真平台。结果表明,相比传统控制策略,所提控制策略母线电压波动得到明显改善,同时蓄电池的输出功率也更加平滑,延长了蓄电池的使用寿命。

Thermal runaway evolution of a 280 Ah lithium-ion battery with LiFePO_(4) as the cathode for different heat transfer modes constructed by mechanical abuse

Lithium iron phosphate batteries have been increasingly utilized in recent years because their higher safety performance can improve the increasing trend of recurring thermal runaway accidents.However,the safety performance and mechanism of high-capacity lithium iron phosphate batteries under internal short-circuit challenges remain to be explored.This work analyzes the thermal runaway evolution of high-capacity LiFePO_(4) batteries under different internal heat transfer modes,which are controlled by different penetration modes.Two penetration cases involving complete penetration and incomplete penetration were detected during the test,and two modes were performed incorporating nails that either remained or were removed after penetration to comprehensively reveal the thermal runaway mechanism.A theoretical model of microcircuits and internal heat conduction is also established.The results indicated three thermal runaway evolution processes for high-capacity batteries,which corresponded to the experimental results of thermal equilibrium,single thermal runaway,and two thermal runaway events.The difference in heat distribution in the three phenomena is determined based on the microstructure and material structure near the pinhole.By controlling the heat dissipation conditions,the time interval between two thermal runaway events can be delayed from 558 to 1417 s,accompanied by a decrease in the concentration of in-situ gas production during the second thermal runaway event.

铝电解槽移动短接母线应用实践

为降低停槽黑电压,缓解电解铝企业的能耗压力,提出在某厂400 kA电解槽安装移动短接母线,并进行实验研究,效果显著,在“能耗双控”背景下,为铝电解行业降低停槽黑电压,进而降低无功能耗提供借鉴。

太阳电池无主栅互联封装技术研究进展

采用无主栅技术降低银浆成本是降低太阳电池组件成本的一个重要方向。主要阐述了无主栅电池组件技术的优势和发展历程,总结对比了覆膜互联、点胶互联、焊接点胶互联几种不同的无主栅电池互联封装工艺,论述了无主栅互联封装技术引入的低温焊丝、聚合物膜新材料、无主栅电池组件的热循环可靠性及不同互联方案对无主栅电池金属化图形的要求,最后对无主栅技术面临的挑战及优化方向进行了展望。

动力电池系统内模组汇流排可靠性浅析

近年来,随着全球环保意识的不断提升,新能源汽车逐渐成为全球汽车产业发展的重要方向,动力电池作为新能源汽车的核心设备,其安全性成为电动汽车发展的关键。行业内针对动力电池系统的热特性开展了大量研究,这些研究大多数只考虑整个动力电池包或者电池模组层面的研究。然而,在动力电池Pack结构设计中,汇流排作为连接的关键零件,其热性能也至关重要。本文以方形动力电池系统内模组研发为基础,论述了电池系统内汇流排的结构设计、强度分析、散热分析方法,同时浅析了过程参数可靠性设置以及产品使用可靠性的验证。希望文中论述的基本过程和基本方法能为电池系统的研发提供一些借鉴。

C_(4)F_(7)N/CO_(2)混合气体在GIS环保型母线中的应用研究

文章对C_(4)F_(7)N/CO_(2)混合气体的特性进行研究,并对其制气方法和混合比测试方法进行了理论分析和应用,在此基础上进行了型式试验验证,为后续在某变电站110 kVGIS环保型母线中的实际应用提供了佐证和试验支撑。研究表明,C_(4)F_(7)N/CO_(2)混合气体能正常满足环保型母线的应用,研究结果可为新型环保GIS设备的研制和应用提供参考。