Effects of current waveform parameters during droplet transfer on spatter in high speed waveform controlled Short-circuiting GMAW

Aim at improving the stability of the Short-circuiting Gas Metal Arc Welding （GMAW-S） process for the enhanced speed usage, effects of current waveform parameters during short-term on the welding stability have been investigated by experimental method. The welding power source used for the research is an inverter with a special current waveform control. It is shown that the spatter decreases at first then increases with each increase of the low current period, current increase rate and the maximum current limit. The test results are provided for welding of 1 mm and 3 mm mild steel at speed of 1.2 m/min. The stable GMA W-S process under high speed welding condition has been achieved by optimizing the parameters.

Analysis of Short-circuit Characteristics and Calculation of Steady-state Short-circuit Current for DFIG Wind Turbine

Large-scale doubly-fed induction generator(DFIG)wind turbines are connected to the grid and required to remain grid-connection during faults,the short-circuit current contributed by the generation has become a significant issue.However,the traditional calculation methods aiming at synchronous generators cannot be directly applied to the DFIG wind turbines.A new method is needed to calculate the short-circuit current required by the planning,protection and control of the power grid.The short-circuit transition of DFIG under symmetrical and asymmetric short-circuit conditions are mathematically deduced,and the short-circuit characteristics of DFIG are analyzed.A new method is proposed to calculate the steady-state short-circuit current of DFIG based on the derived expressions.The time-domain simulations are conducted to verify the accuracy of the proposed method.

Short-circuit Current Characteristics of Wind Generators

To study the effects of wind generators on distribution system protection,the short-circuit current(SCC) characteristics of wind generators is important.Although there are many researches on the issue,a clear agreement has not been reached so far.The SCC characteristics for different wind generators are studied.PSCAD simulation is performed in the same system integrated with different kinds of wind generators,and their results are compared with those reported in IEEE papers.The detection possibility by overcurrent relay(OCR)is discussed based on the simulation results.

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.

星-三角接法的分数槽永磁电机匝间短路故障分析

为了分析永磁电机绕组采用星-三角(Y-△)接法时发生匝间短路故障后对电机的影响,建立了绕组在Y-△接法下分别在星形(Y)接法部分和角形(△)接法部分发生匝间短路故障的电路模型,推导得到故障发生后电机三相电流。以10极12槽永磁电机为例进行二维有限元仿真,对传统的Y接法双层绕组永磁电机和Y-△接法4层绕组永磁电机发生匝间短路故障的情况进行对比分析。仿真结果表明:在Y-△接法下匝间短路故障位置的不同对电流会有很大影响;在发生匝间短路故障后Y-△接法能降低电机的转矩脉动,降低故障发生后故障相电流中的3次谐波幅值。

基于MMC主动限流的VSC-HVDC双极短路故障控保协同策略

直流故障保护是柔性直流输电系统发展面临的主要挑战之一,利用模块化多电平换流器(MMC)的灵活控制实现限流已成为当前研究的热点。MMC的主动限流降低了故障电流变化率和故障电流幅值,易引起故障判断以及保护选择困难。文中以对称单极接线的柔性直流系统为研究对象,采用控保协同思想,将主动限流控制与故障识别相结合,提出了基于主动限流因子的故障区域识别与区分方法实现双极短路故障的区域识别与切除。首先,通过在MMC电流内环控制器中附加故障电流目标预设控制器,在故障发生后可快速跟踪故障电流的变化,自适应地调整MMC输出的直流电压将故障电流控制在预设目标参考值附近;其次,根据不同故障位置时故障电流目标预设控制器输出的限流因子快速确定故障区域。最后,在PSCAD/EMTDC中对四端柔性直流输电系统的不同故障场景进行了仿真分析,验证了所提控保协同策略的可行性和有效性。

含主动限流控制的MMC-HVDC电网直流短路故障电流解析计算

传统的MMC-HVDC电网直流短路故障电流计算一般采用等效RLC电路方法。但是该方法没有考虑主动限流控制(ACLC)对等效电路RLC参数的影响,因此无法直接用于含ACLC的MMC-HVDC电网的直流短路故障电流的解析计算问题。该文通过将ACLC的控制效果等效为虚拟阻抗产生的压降,建立了体现ACLC的控制影响的等效RLC电路,以包含电流变化率限流环节的典型ACLC算法为例,推导了直流双极短路故障条件下ACLC的控制参数与虚拟阻抗的映射关系以及相应的直流故障电流解析表达式。最后,以基于含ACLC的半桥型四端MMC-HVDC电网为例,建立PSCAD/EMTDC仿真模型,对采用ACLC的直流双极短路故障电流解析计算结果进行了验证。结果表明:故障后10ms内直流短路故障电流的PSCAD仿真结果与所提出的含ACLC的等效RLC电路解析计算结果的平均误差在8.29%以内,最大误差在10.99%。因此,使用所提出的方法具有工程实用性。

Influence of optical interference and carrier lifetime on the short circuit current density of organic bulk heterojunction solar cells

Based on simple analytical equations, short circuit current density （Jsc） of the organic bulk heterojunction solar cells has been calculated. It is found that the optical interference effect plays a very important role in the determination of Jsc; and obvious oscillatory behaviour of Jsc was observed as a function of thickness. At the same time, the influence of the carrier lifetime on Jsc also cannot be neglected. When the carrier lifetime is relatively short, Jsc only increases at the initial stage and then decreases rapidly with the increase of active layer thickness. However, for a relatively long carrier lifetime, the exciton dissociation probability must be considered, and Jsc behaves wave-like with the increase of active layer thickness. The validity of this model is confirmed by the experimental results.

电磁-结构场耦合下变压器绕组漏磁场和变形仿真研究

电力变压器发生短路故障时会产生巨大的电动力,为研究电力变压器短路故障时的绕组变形情况以及影响绕组变形的因素,文中基于变压器多物理场耦合理论,搭建了三相变压器的有限元模型,通过MATLAB/Simulink平台仿真变压器发生短路时的短路电流,将该电流作为电磁场仿真的激励,计算出绕组的漏磁场和电动力分布,再采用电磁-结构场耦合的方法分析绕组的形变量大小和应力分布;运用相关理论分析不同温度条件对绕组变形的影响。结果表明,在辐向上,高压绕组受到向外膨胀的辐向电动力,中压和低压绕组受到向中间压缩的辐向电动力,在轴向上,各绕组均受到从端部向中间压缩的电动力,温度越高,绕组铜的杨氏模量越小,相同电动力作用下绕组变形量越大。研究结果对提高变压器抗短路能力具有一定的参考意义。

基于UL60335-2-40的空调机组控制面板短路电流额定值的确定方法

北美市场空调机组产品遵循UL 60335-2-40标准,UL 60335-2-40定义了空调机组控制面板需要标识短路电流额定值。本文总结了如何基于UL 60335-2-40及UL 508A的要求确定空调机组控制面板短路电流额定值的流程,为空调机组控制面板的短路电流额定值的确定提供了参考。

Study on Short Circuit Current Calculation of Power System with UHVDC and New Energy Source

With the development of power system, the level of short circuit current will increase accordingly. In general, the influence of the HVDC system and the new energy source is not considered in the calculation of the short circuit current. For the power grid that short circuit current level closes to the interrupting capacity of circuit breaker, it’s necessary to fully consider all kinds of influence factors, careful checking, so as to obtain more accurate calculation results of short circuit current. In 2018, two ±800 kV high-power Ultra High Voltage Direct Current (UHVDC) transmission projects will be connected with Shaanxi power grid, accompanied by a lot of concomitant fossil-fuel generating plants as power resource, and also a large number of new energy source, includes wind power generation and photovoltaic power generation. Around one of the UHVDC converter stations, short circuit current may exceed the withstand limit of some certain circuit breakers. In order to get more accurate short circuit current calculation results, three measures are used: 1) contrastive calculation and analysis by algorithm based on schemes and algorithm based on power flow;2) analysis the influence of UHVDC by electromagnetic transient and electromechanical transient hybrid simulation;3) considered a detailed model of Doubly Fed Induction Generator (DFIG) with low voltage ride through characteristics. The calculation results shows that: in the typical operation mode of Shaanxi power grid of 2018, the original calculation results by conventional calculation method are coincident with the results by considering the influence of algorithms, UHVDC and DFIG in large, in which: the results of the algorithm based on power flow are smaller than that of the algorithm based on schemes about 2 - 8 kA;the steady values of the short circuit current provided by UHVDC converterstation (includes rectifiers and smoothing capacitors) are about 0 - 3 kA;the steady values of the short circuit current provided by DFIG are about 0 - 5 kA. The calculation results can provide reference for the selection of the circuit breaker, and it can be verified by fault recording data in the future.

基于智能模块化-48V通信直流电源的短路测试研究

随着锂电池产业的成熟,锂电池的能量密度高、体积小、寿命长的优势以及其经济性的不断优化,在通信电源系统中的应用越来越广泛。但是锂电池以及特别是带有双向DC/DC的智能锂电池,出于安全性、经济性的综合考虑,其实际运行中的短路放电能力和传统铅酸电池相比,明显存在很大差距,在电源系统设计和配电选择性保护的安全设计中存在极大隐患,甚至可能引起火灾重大事故的发生。文章以智能模块化电源系统为研究对象,介绍了系统的主要构成以及配套电池进行短路测试研究。并在本文中总结了目前智能模块化系统在短路故障时所存在的问题,对智能模块化系统短路故障保护技术的研究进行了展望。

Study on Effect of UHV Power Grid Construction Schemes on Short Circuit Current

The commissioning of Southern Hami-Zhengzhou ±800 kV UHVDC transmission project has important significance to heighten operation reliability, transfer capability and supply electric ability of Henan power grid. However, short circuit currents of 500 kV buses in the Center of Henan are almost close to the operation upper limitation. In order to decrease the short circuit currents effectively, it’s necessary to strengthen the network structure of Center of Henan power grid and calculate short circuit currents. Two schemes of strengthening the network structure of Center of Henan power grid are studied. The calculated values of short circuit currents of some important 500 kV buses in the two schemes are still bigger than excepted. According to the latest Plan of State Grid, Yubei UHV substation and Zhumadian UHV substation located in Henan power grid. The calculated values of short circuit currents of some important 500 kV buses with the commissioning of Yubei UHV and Zhumadian UHV are qualified. So, reasonable network structure with UHV is suitable to heighten transfer capability and supply electric ability of Henan power grid.

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%.

DW450-1600操作机构在65 kA短时耐受时的强度分析

基于UG动力学仿真,建立DW450-1600低压断路器的仿真模型。基于Maxwell电磁场仿真,建立低压断路器合闸状态下的触头系统仿真模型,计算出65 kA短时耐受下触头系统所受电动斥力。再将Maxwell求出的电动斥力数据耦合至UG动力学仿真,计算出65 kA短时耐受下DW450-1600操作机构的受力情况。最后基于UG有限元仿真,建立DW450-1600操作机构的仿真模型,对操作机构零部件进行强度分析。结果表明,DW450-1600操作机构在65 kA短时耐受电动斥力的作用下受力情况有明显影响。

VSC-HVDC系统中IGBT阀保护方案研究

针对电压源换流器的高压直流输电(VSC-HVDC)系统,首先分析正常运行情况下电压源换流器两侧交、直流电流之间满足的平衡关系。然后将换流器的5种开关模式按照桥臂导通状态分为两类工作状态,分析不同工作状态下全控型电力电子器件绝缘栅双极晶体管(IGBT)阀短路和阀开路的电流流通路径,研究故障后交流侧电流幅值和直流侧电流的变化及其相互关系。在此基础上,提出一种能够反应IGBT阀短路和阀开路的保护方案,将交流侧三相电流采样值分别与各自导通状态函数相乘并求和,并与直流侧电流采样值构成差动电流,利用该差动电流反应阀短路和阀开路故障,并给出保护的整定原则。最后,基于仿真平台搭建双端VSC-HVDC系统模型,验证了该保护方案的有效性。

计及零直流电压控制的混合型MMC-HVDC输电系统短路电流计算方法

混合型模块化多电平换流器通过零压控制限制直流侧故障电流,为准确分析计算故障后直流侧电流,考虑不同阶段控制系统作用建立其等值模型,并设计故障电流求解计算方法。在零压控制前,构建混合型MMC的串联RLC等值模型,利用受控电流源表征交流馈入能量对故障电流的影响;在零压控制后,分析上下桥臂电压动态调整对故障电流的影响,构建相应混合型MMC等值模型提高计算精度。采用状态空间方程计算2个阶段的直流短路电流,通过电容电压置零来计及零压控制后子模块投切引起直流侧电压复零的特性。基于MATLAB/Simulink仿真平台搭建了双极混合型MMC直流输电系统,在不同工况下通过与详细电磁暂态仿真结果对比,验证了所提短路电流计算方法的准确性。

碱性锌-二氧化锰电池三参数测试设备的改进

碱性锌-二氧化锰(碱锰)电池在生产过程中及出厂前要进行相关参数的检验,以保证品质。传统的测试设备和方法在稳定性、误差、速度和精度等方面存在一定问题。对碱锰电池三参数测试设备和测量方法进行改进,以提高稳定性、减少误差。根据具体测量项目进行补偿的取舍:9 V电池负载电压测试时,需加补偿;短路电流测量时,需全面考虑补偿问题。选择电气检测元件时,要考虑元件精度和环境温度等的影响。三参数检测电路的计算误差控制在4‰以内。通过设备设计、安装和调试,检测速度达到0.1 s/组,三参数检测总体精度控制在5‰以内。

计及风光相位特性和机-网间元件的短路电流计算方法

以风电和光伏为代表的新能源机组大量接入电网使得短路电流的精确计算校核变得困难。针对最新研究中构建新能源并网点短路电流映射模型时,未考虑相位映射及未计及箱变、集电线路、主变及送出线路等机端到并网点间电气元件(机-网间元件)影响的理论缺陷,文中提出一种计及新能源相位特性和机-网间元件影响的改进工程化电网短路电流计算方法。首先,结合国家运行规程对新能源机端电压-短路电流相位映射进行有补充意义的理论建模。其次,对该模型进行工程化处理,并提出一种将所得映射逆推至并网点的迭代计算方法。继而,将工程化后的并网点短路电流幅相映射模型应用到现有局部迭代计算中,得到改进的计算方法。最后,在PSCAD仿真软件中搭建新能源并网模型,验证了新能源机端电压-短路电流理论幅相映射的准确性、机端映射模型逆推至并网点的迭代计算理论有效性;在此基础上,在IEEE 39节点系统中对所得映射模型进行实验验证。结果表明所提改进计算方法能在一定程度上提升短路电流计算精度。