变压器励磁涌流对冶金负荷的影响

在一起冶金企业变电站倒闸操作中,由于对变压器低压侧反充电产生励磁涌流,造成相邻负荷的误跳闸事故,文章分析了励磁涌流产生的机理、影响因素、特征及其对电网负荷的影响,并对稳定措施进行了初步探讨。     

变压器保护励磁涌流探讨

变压器保护的一个主要技术问题是解决变压器励磁涌流的问题,即如何解决空投变压器于内部故障(尤其是匝间故障)时差动保护动作速度慢的问题;同时在变压器各种空投时产生的励磁涌流、区外故障切除后产生的恢复性涌流以及和应涌流等状态下差动保护不误动。这个课题一直是国内外变压器保护研究的热点。     

变压器空载投入时差动保护误动作原因分析

论述了变压器空载投入时差动保护误动作原因是由励磁涌流引起的,分析了励磁涌流的产生、危害及其特点。     

基于动态阻抗特性的变压器励磁涌流判别方法

变压器差动保护是变压器保护的主保护之一。目前,变压器差动保护在如何准确鉴别励磁涌流和故障电流这个问题上存在不足。为更有效地辨别变压器的励磁涌流和内部故障电流,提出了基于动态阻抗特性的变压器励磁涌流判别方法。     

变压器激磁涌流产生原因及对策分析

励磁涌流是一种暂态过程,变压器空载投入时可能会出现高达6-8倍的额定电流,而类似这种可流入差动回路的电流往往会导致差动保护动作的发生。因此,分析研究励磁涌流是如何发生及发生时对变压器差动保护的影响和解决方案是非常有必要的。     

一种380V/660V双电压隧道凿岩台车电气控制系统

为了解决隧道凿岩台车在380V和660V两种供电环境中切换电机及控制变压器接线非常不方便的状况,提供一种实现交流额定电压380V和660V控制的凿岩台车电气系统,只需要通过电压等级转换开关来切换大功率的主油泵电机的星角降压启动方式和星形直接启动方式。另外两个功率较小的电机为380V供电的直接启动方式不变。当供电电压660V时,通过电压等级切换开关自动切换为由一个专用660V/380V变压器给两个小功率电机以及控制变压器供电。     

电能质量电压暂降问题及应对方案

介绍了电压暂降产生的原因和危害及电压暂降相关的国际标准,叙述了电压补偿型装置、失压脱扣装置和高压供电安全防护墙等电压暂降应对方案,指出电压暂降问题需从供电侧和用电侧同时考虑、分别治理,依据标准,针对不同用户和设备特性,采取减少或消除电压暂降冲击的手段,以达到满意的动态电能质量需求.     

电压暂降及短时中断治理技术浅析

外部电网或内部电网故障会导致电压暂降或短时中断，造成设备跳闸，给企业生产带来极大影响。通过对电压暂降的成因及对敏感设备的影响分析，提出了采用快速涡流驱动高速开关、区内外短路电压暂降治理、零损耗限流技术及主动干预型消弧选线技术等治理措施，并详细论述了其工作原理。采用电压暂降治理关键技术可将电压暂降持续时间压缩在20 ms（周波级）内，可有效避免敏感设备停运。     

复合磁路三相定子混合励磁双凸极直流发电机及其时步有限元分析

复合磁路三相定子混合励磁双凸极直流发电机的励磁线包和永磁体在与转轴正交的同一剖面上,电励磁磁通和永磁磁通复用电机磁路具有励磁功率小、励磁调节范围可按要求设计、可以实现单输出或双路输出的特点.文章介绍了该型电机的典型结构,使用时步有限元法分析其工作模态,基于场分析结果提取电感特性,计算比较空载特性、外特性,仿真计算了双路输出的开环调整率.分析结果表明,该电机既能作为独立供电系统的无刷直流发电机,又能并网发电,特别适于航空和其他野外作业场合高速发电机用,并实现起动/发电一体化,应用前景广泛.     

一起变压器励磁涌流造成线路纵差保护误动原因分析及对策

介绍了某钢铁厂110 kV变电站发生的一起因下级站所电炉变压器送电产生的励磁涌流,进而造成35 kV线路光纤纵差保护误动作的事故案例,总结分析了线路纵差保护中电流互感器发生暂态饱及保护装置保护原理共同作用下光纤纵差保护误动作的原因,并针对此案例提出此类型事故的解决对策。     

Taking the V out of genes V environment

Tumor necrosis factor-alpha (TNF-alpha) is thought to be an important mediator in the pathogenesis of neonatal septicemia. To assess the role of TNF-alpha in neonatal sepsis, serum levels of TNF-alpha were measured in a group of neonates with septicemia and compared with the levels of gestational-postnatal, age-matched healthy controls. The relationships between severity of infection, the nature of causative microorganisms, and TNF-alpha levels were also investigated in this prospective study. A total of 49 infants (25 full-term, 24 preterm) with proven sepsis and 40 healthy infants (20 full-term, 20 preterm) were included. Serum TNF-alpha levels were measured using the TNF-alpha immunoradiometric assay. The median level of TNF-alpha was found to be significantly higher in infants suffering from sepsis (154 pg/mL) particularly in those with septic shock (242.5 pg/mL) as compared to healthy controls (61.5 pg/mL) (p < 0.001). No correlation was found between TNF-alpha and postnatal ages, gestational ages or birth weights of the infants. TNF-alpha levels were not different in surviving and terminal neonates. Although serum, TNF-alpha levels were found to be slightly higher in gram-negative septicemia, the difference was not significant. These findings suggest that TNF-alpha plays an important role in the pathophysiology of neonatal septicemia, but its importance as a prognostic factor is not yet clear.     

Cortical feedback improves discrimination between figure and background by V1, V2 and V3 neurons

A single visual stimulus activates neurons in many different cortical areas. A major challenge in cortical physiology is to understand how the neural activity in these numerous active zones leads to a unified percept of the visual scene. The anatomical basis for these interactions is the dense network of connections that link the visual areas. Within this network, feedforward connections transmit signals from lower-order areas such as V1 or V2 to higher-order areas. In addition, there is a dense web of feedback connections which, despite their anatomical prominence, remain functionally mysterious. Here we show, using reversible inactivation of a higher-order area (monkey area V5/MT), that feedback connections serve to amplify and focus activity of neurons in lower-order areas, and that they are important in the differentiation of figure from ground, particularly in the case of stimuli of low visibility. More specifically, we show that feedback connections facilitate responses to objects moving within the classical receptive field; enhance suppression evoked by background stimuli in the surrounding region; and have the strongest effects for stimuli of low salience.     

Dual conformations of a T cell receptor V alpha homodimer: implications for variability in V alpha V beta domain association

The crystal structure of a mutant T cell receptor (TCR) V alpha domain containing a grafted third complementarity-determining region (CDR3) from a different V alpha was determined at 2.3 A resolution by molecular replacement using the wild-type V alpha structure as a search model. Like the wild-type V alpha domain, the mutant crystallized as a homodimer very similar to TCR V alpha V beta and antibody V(L)V(H) heterodimers, with the CDR loops disposed to form part of the antigen-binding site. However, the relative orientation of the two chains in the mutant V alpha homodimer differs from that in the wild-type by a rotation of 14 degrees such that the buried surface area in the dimer interface of the mutant is 140 A2 less than in the wild-type. While the residues forming the interface are essentially the same in the two structures, there are only four pairs of interface hydrogen bonds in the case of the mutant compared with eight for the wild-type. These results suggest that multiple relative orientations of the V alpha and V beta domains of TCRs may be possible, providing a significant contribution to TCR combining site diversity.     

Factor V Quebec revisited

Factor V Quebec has been described as a bleeding disorder that exhibits an autosomal dominant inheritance pattern and presents severe bleeding after trauma. Two members of a fourth-generation (IV.13 and IV.15) Canadian family have been studied in detail and are the subject of this report. Their clinical presentations and histories have been described previously (Tracy et al: J Clin Invest 74:1221, 1984). Persistent abnormalities include mild thrombocytopenia and defective platelet factor V. Plasma factor V is present at near normal concentration and is fully functional. Thus, the bleeding diathesis appears to reflect the absence of platelet factor V activity. The recent report (Hayward et al: Blood 84:110a, 1994 [suppl, abstr]) of multimerin deficiency in these individuals led us to reevaluate these patients. Western blot analyses of platelet lysates developed with a variety of monoclonal antibodies show that the alpha-granule proteins, fibrinogen, von Willebrand factor, factor V and osteonectin are decreased in concentration and significantly degraded in the platelets of these patients. Thrombospondin, while not degraded, is substantially decreased. In contrast, platelet factor 4 and beta-thromboglobulin do not appear to be affected. These observations suggest that the alpha-granules are correctly assembled but the contents are subsequently subjected to proteolytic degradation. The results indicate that factor V Quebec disorder is probably associated with a generalized defect that leads to degradation of most proteins of the alpha-granules.