冶金企业电压凹陷分析与治理

冶金企业电压凹陷严重困扰了企业的发展,对企业正常生产秩序扰动很大,简单的外部事故或内部故障以及非正常停电,时常造成电网电压大幅波动或短时断电情况,导致重大损失。对此进行大力整治,有效地解决了失电及电压凹陷对供电系统的影响,确保了供电系统的安全运行。先进的控制方法以及策略的应用,实现了企业电网的可靠、安全、经济、高效运行目标,同时还介绍了电压凹陷的产生机理和解决方案。     

供电系统失电及电压凹陷问题的治理

宝钢不锈钢有限公司供电系统由于外部事故或内部故障以及非正常停电,时常造成电网电压大幅波动或短时断电情况,造成重大损失。结合高炉风机房低压改造项目,对变电所进行了电源快切以及控制电源UPS技术改造,有效地解决了失电及电压凹陷对供电系统的影响,确保了鼓风机的安全运行。     

冶金企业连续生产抗电压凹陷技术的研究探讨

由于冶金企业对生产连续性的要求,以及供用电系统的电压凹陷现象对企业正常生产造成的严重影响,使得企业必须对各种电气设备做好抗电压凹陷措施,来避免或减小电压凹陷给企业正常生产带来的损失。探讨了抗电压凹陷技术在酒钢的应用。     

冶金企业电压互感器二次电压异常分析及应急处理

电压互感器是电网中的重要设备,二次电压异常是常见的电容式电压互感器故障表征形式,分析了电容式电压互感器的工作原理和等效回路特性,研究了互感器内部各种元件故障引起二次电压异常的机理,发生故障时采取针对性措施进行处理。     

钢铁企业电压凹陷影响及治理浅析

针对电压凹陷带来的严重危害及产生的原因，进行了系统性的分析和研究，实施了有针对性的系统治理改造及运行方式调整，有效降低了电压凹陷故障的频次和影响范围。     

不对称故障下双馈风力发电系统网侧变流器的控制方法

风力发电机组通过背靠背变流器与电网相连接,电压发生不对称故障时直流侧电压将发生大幅波动,而要消除这方面的影响,关键在于对网侧电流的控制.针对电网电压不对称故障下风电机组的表现,文章提出了一种适用于该情况下的网侧变流器的控制策略,以实现风电机组的低电压穿越.对发生不对称故障时网侧变流器的状态进行分析,得出其控制指令,使用Matlab/Simulink建立仿真模型,给出A相电压发生50%跌落下的仿真结果,验证了该控制策略的可行性.     

板坯连铸变频抑制电压凹陷治理解决方法分析

基于板坯连铸机控制系统的技术分析,讨论当公司电网故障时导致板坯连铸机生产电压凹陷中断的情况,产生板坯连铸机突然浇铸中断。结果表明,板坯铸坯出现严重的卧坯;铸机的振动、拉矫停止工作死锁重新启动,导致铸机处于过程瘫痪,造成严重的设备损坏损失。     

谐振过电压造成中性点不接地电网“虚接地”现象的分析

本文根据水钢电网的运行情况，对电网电压发生不平衡现象进行分析，以及怎样对中性点不接地电网的单相接地故障与出现的“虚接地”现象进行判断，提出处理和消除措施。     

水钢电网铁磁谐振故障与单相接地故障的判别与处理

本文根据水钢电网的运行情况，对电网电压发生异常现象绝缘监视装置发出“接地”信号时的正确判别，以及怎样对中性点不接地电网的单相接地故障进行判别，提出处理和消除措施，以缩短电网故障时间，确保电网的安全运行。     

66kV系统消弧线圈加装消谐阻尼装置的论证

以鞍钢电网为例，分析了当前电网经常发生虚幻接地现象和三相电压不平衡的根本原因，提出了加装消谐阻尼装置的设计基本原则，以及不同容量的消弧线圈所配阻尼电阻值的计算方法。     

矿山企业节能与无功功率补偿

功率因数的高低关系到电力网中的功率损耗和电能损耗,提高电力系统的功率因数,有利于矿山企业节能.文中分析了影响电网功率因数的主要因素、低压电网无功补偿的常用方法及无功补偿的效益.     

高压同步电动机液态软启动及其自动控制

本文介绍了液体软启动的原理,以及使用Ouantum系列PLC实现高压大功率同步电动机起动过程的自动控制,及其运行过程中的自动监控。对比分析了全压起动与降压起动对电网电压及电机的影响。     

Hyperpolarization-activated inward current in neurons of the rat's dorsal nucleus of the lateral lemniscus in vitro

Hyperpolarization-activated inward current in neurons of the rat's dorsal nucleus of the lateral lemniscus in vitro. J. Neurophysiol. 78: 2235-2245, 1997. The hyperpolarization-activated current (Ih) underlying inward rectification in neurons of the rat's dorsal nucleus of the lateral lemniscus (DNLL) was investigated using whole cell patch-clamp techniques. Patch recordings were made from DNLL neurons of young rats (21-30 days old) in 400 micro;m tissue slices. Under current clamp, injection of negative current produced a graded hyperpolarization of the cell membrane, often with a gradual sag in the membrane potential toward the resting value. The rate and magnitude of the sag depended on the amount of hyperpolarizing current. Larger current resulted in a larger and faster decay of the voltage. Under voltage clamp, hyperpolarizing voltage steps elicited a slowly activating inward current that was presumably responsible for the sag observed in the voltage response to a steady hyperpolarizing current recorded under current clamp. Activation of the inward current (Ih) was voltage and time dependent. The current just was seen at a membrane potential of -70 mV and was activated fully at -140 mV. The voltage value of half-maximal activation of Ih was -78.0 +/- 6.0 (SE) mV. The rate of Ih activation was best approximated by a single exponential function with a time constant that was voltage dependent, ranging from 276 +/- 27 ms at -100 mV to 186 +/- 11 ms at -140 mV. Reversal potential (Eh) of Ih current was more positive than the resting potential. Raising the extracellular potassium concentration shifted Eh to a more depolarized value, whereas lowering the extracellular sodium concentration shifted Eh in a more negative direction. Ih was sensitive to extracellular cesium but relatively insensitive to extracellular barium. The current amplitude near maximal-activation (about -140 mV) was reduced to 40% of control by 1 mM cesium but was reduced to only 71% of control by 2 mM barium. When the membrane potential was near the resting potential (about -60 mV), cesium had no effect on the membrane potential, current-evoked firing rate and input resistance but reduced the spontaneous firing. When the membrane potential was more negative than -70 mV, cesium hyperpolarized the cell, decreased current-evoked firing and increased the input resistance. Ih in DNLL neurons does not contribute to the normal resting potential but may enhance the extent of excitation, thereby making the DNLL a consistently powerful inhibitory source to upper levels of the auditory system.     

Electrical rolling of a metal powder in roll electrodes with a high-density current

The effect of roll electrode voltage on the electrical rolling of metal powders is considered. Formulas for voltage computation during electrical rolling are derived. The breakdown voltages of powder materials are determined experimentally. The optimum values of voltage during the electrical rolling of widespread metal powders are established.     

Computer model of gastric electrical stimulation

The aim of the study was to simulate gastric electrical stimulation using a computer model of gastric electrical activity and suggest a possible avenue toward reliable gastric pacing. Modeling was based on the conoidal dipole model of gastric electrical activity described earlier. It was assumed that local, nonpropagated contractions can be produced circumferentially using 4 rings of stimulating electrodes supplied with 2-sec phase-locked bipolar trains of 50 Hz, 15 V (peak to peak) rectangular voltage. Temporal and propagation organizations of gastric electrical activity described in the conoidal dipole model were used to derive the geometry of the stimulating electrodes and the time shifts for phase-locking of the electrical stimuli applied to the different circumferential electrode sets. The major assumptions and findings of the model were tested on two unconscious dogs. The model produced completely controllable simulated gastric contractions that could be propagated distally by phase-locking the stimulating voltage. The values of interelectrode distances in different rings, as well as the distances between the successive rings, were also derived. The concept of invoked circumferential contractions that are artificially propagated by phase-locking the stimulating voltage could be an avenue toward reliable gastric pacing of gastroparetic patients.     

Electrical membrane properties of trapezoid body neurons in the rat auditory brain stem are preserved in organotypic slice cultures

The medial nucleus of the trapezoid body (MNTB) is a conspicuous structure in the mammalian auditory brain stem. It is a major component of the superior olivary complex and is involved in sound localization. Recently, organotypic slice culture preparations of the superior olivary complex were introduced to investigate the development of inhibitory and excitatory projections (Sanes and Hafidi, 1996; Lohmann et al., 1998). In the present article, we further assessed the organotypicity of our culture system (Lohmann et al., 1998) and examined electrical membrane properties of MNTB neurons expressed under culture conditions. To do so, MNTB neurons from early postnatal rats (P3-5) were studied after 3-6 days in vitro (DIV) by whole-cell patch-clamp recordings. Their mean resting potential was -59 mV, the input resistance averaged 171 Momega, and the average time constant was 3 ms. Four types of voltage-activated conductances were observed in voltage-clamp recordings. All cells expressed a tetrodotoxin (TTX)-sensitive sodium current. Two types of potassium currents could be characterized: a tetraethylammonium (TEA) -sensitive and a 4-aminopyridine (4-AP)-sensitive conductance, both of which are composed of a transient and a sustained component. Finally, an inwardly rectifying current, activated by hyperpolarizing voltage steps, was found. In current-clamp recordings, depolarizing current pulses typically elicited a single action potential. In the presence of 4-AP, however, these current pulses induced a train of action potentials. The duration of action potentials was increased by 4-AP and the afterhyperpolarization was reduced. Hyperpolarizing current injections induced a "sag" in the membrane potential, indicating the influence of an inwardly rectifying current. Our results demonstrate that MNTB neurons in slice cultures have electrical membrane properties comparable to those of their counterparts in acute slices.     

韶钢35kV配电网运行中存在的问题及对策

35kV配电网自2002年在韶钢运行以来,解决了小区块供电问题,并具有明显的节电效果．但是,随着韶钢35kV电网规模的不断扩大,影响35kV配电网安全可靠运行的因素逐年增多．文章分析了韶钢35kv配电网运行中存在的主要问题,提出了具体对策,对改善韶钢35kV配电网安全可靠供电发挥了积极的作用．     

SVC在莱钢超高功率电弧炉上的应用

阐述了电弧炉冶炼时所产生的无功冲击、谐波电流、负序电流等对电网及电气设备的影响,并以莱钢特殊钢厂50 t超高功率电弧炉应用德国西门子SVC技术为例,阐述了SVC设置的原则,SVC主接线和SVC的控制原理等。SVC投入运行后,对非线性负荷产生的谐波电流,电压波动及闪变等引起供电电能质量的问题起到了很好的治理效果。     

珠钢150t天车电气控制系统改造

珠钢150 t天车整车电气控制系统的改造采用了西门子PLC及SIMOTRAS HD定子调压调速装置。以PLC为控制核心,取代旧式的继电器逻辑控制;机构电机驱动控制采用SIMOTRAS HD定子调压调速装置与转子切换电阻相配合的调速方式,取代传统的电机转子接触器控制切换串电阻的调速方式,以解决原控制系统的不稳定及电动机调速性能差的问题。系统自2008年使用至今,不但控制系统稳定性提高,而且各机构的电动机在启动、停止、运行过程中速度都很稳定,电气故障率明显下降。