Charge relaxation due to surface conduction on an insulating sheet near a grounded conducting plane

Electrostatic charges are responsible for a variety of problems in industrial processes and customer equipment that use webs or sheets. Problems include particle contamination from attracting dust, sheets that stick to each other, and electrical discharges resulting in logic resets or damage to electrical components. These problems can be mitigated by increasing the surface conductivity of the insulating sheets by coating the surface with a conductive layer or by increasing the relative humidity. To mitigate problems, electrostatic charge must dissipate quickly compared with the mechanical transport time of the process. Reported here are the results of a model calculation of the charge relaxation time showing explicitly that the charge relaxation time depends on both surface conductivity and geometry. The charge relaxation time is found to increase as the distance to a nearby, grounded conducting plane decreases. Charge relaxation is slowed because the tangential electric field needed to drive surface current becomes smaller as the distance to the grounded plane decreases. Inferred from this analysis is the dependence of charging on the electric Reynolds number (ratio of the electrical charge relaxation time to the mechanical transport time). Web charging can be divided into three regimes: dissipation (R/sub e/<0.1), transition (0.1相似文献   

Detection of parallel discharges in gas insulated substations

Four methods for partial discharge (PD) detection in gas-insulated substations were considered. Laboratory tests were carried out to determine the efficiency of these methods to detect defects and to discriminate among different defect types. The sensitivity of the methods is compared and the applicability of the methods in the field is discussed. In the laboratory the standard PD measuring method showed a good sensitivity to defects. In the field condition the standard PD measuring method can have a sensitivity much lower than in laboratory, due to the rather high noise level expected. In the laboratory two of the alternative PD detection methods (namely the acoustic method and electrical method including a field probe inside the GIS) have shown a sensitivity to fixed-type defect discharges, while showing less efficiency relative to the mobile particles considered in the study     

平行集束电缆的制造及新型模具设计

本文就平行集束电缆生产中常见的质量问题提出了相应的措施 ,还设计了一种新型挤出模具 ,可较好的解决绝缘偏心问题     

Characteristics of partial discharges caused by trees in contact with covered conductor lines

Characteristics of partial discharges (PD) caused by trees in contact with covered conductor (CC) lines have been studied. A tree in contact with a CC distorts the electric field around the conductor and causes partial discharges. According to tests conducted in a high voltage laboratory the rise time of the PD current pulses caused by the trees is relatively long, in the order of 60 ns...0.8 μs. The fault impedance and PD magnitude caused by a tree in contact with a CC and the propagation attenuation of PD pulses was studied in different seasonal conditions in September, November and March on a full scale 110 kV CC trial line. In case of an intact CC the fault impedance is several MΩ. After breakdown of the conductor covering the fault impedance collapses in summer to tens and in winter to hundreds of kΩ. The average PD magnitude measured in March was approximately one fifth of that in September. On a 9.3 km line portion the observed propagation attenuation of the PD signal was 0.37...3.7 dB. The variation in the attenuation is attributed to the variation in the rise times of the PD pulses and the modal composition of the PD signal. The results indicate that PD measurements can be used to detect trees fallen on CC lines.     

平行集束导线在昆明农网建设中的应用

阐明平行集束导线及其特点,介绍平行集束导线在昆明市官渡区六甲乡福保村农网建设与改造中的应用情况.     

Field calculations in a moving conductor by an integral equation

Contents The equation for the magnetic field in a moving conductor is derived. After calculating the Green's function of this equation an integral equation formulation of the problem will be put forward. This equation will be solved numerically for a particular example.

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Integralgleichungsverfahren zur Feldberechnung in bewegten Leitern

Übersicht Die Gleichung für das magnetischen Feld in einem bewegten Leiter wird abgeleitet. Nach Berechnung der Greenschen Funktion der Originalgleichung wird die Formulierung des Problems mittels einer Integralgleichung vorgestellt. Dieses Problem wird in einem geeigneten Beispiel numerisch gelöst.

     

并联运行电动机短路故障仿真及保护对策

2台并联运行的异步电动机,当一台电动机发生三相或两相短路故障被电流速断保护装置切除时,会引起另外一台正常运行的电动机电流增大,超过其额定电流4倍以上,导致正常运行电动机的速断保护误动作而跳闸。基于Matlab建立2台异步电动机并联运行时短路故障的仿真模型,研究分析了产生上述情况的机理、不同类型故障的影响程度及故障信号特征,并提出了带方向元件的电流速断保护的新方案,该方案既防止了正常运行电动机电流速断保护的误动作,又不影响故障电动机电流速断保护的正确动作。动模试验证明了该方法的正确性。     

Modeling of a buried conductor for an electromagnetic transient simulation

The paper has proposed a distributed‐line model of a buried bare conductor with horizontal and vertical configuration by assuming an artificial insulator outside of the bare conductor so that the characteristic impedance and the propagation velocity of the buried conductor is evaluated as an insulated conductor (cable) by the cable constants/parameters of the EMTP. A shunt admittance is added to the conductor at every short distance to represent currents flowing into the earth from the original bare conductor. The admittance circuit and the parameters are evaluated either by experimental results or by published references of grounding electrodes. The model circuit has been applied to simulate transient currents and voltages on horizontal and vertical buried conductors, and the simulation results are compared with the measured results. It has been observed that the simulation results of the currents agree satisfactorily with the measured results, but the results of the voltages do not seem satisfactory. The reason for this has been discussed based on the measured results. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于多台APF并联的微网谐波抑制

针对微网中的谐波问题,对多台有源滤波器(APF)的并联运行治理微网谐波进行了研究,在比较并研究了均流策略和各种并联策略后,提出了一种新的微网中APF并联方法和控制策略,研究了均流策略和并联实现方法。通过仿真验证了该方法的可行性和可靠性,说明该方法具有很好的动态性能和补偿效果。     

A theoretical analysis of the propagation properties of the twisted-wire pair running above a ground plane

Electromagnetic coupling between neighboring circuits can be mitigated using twisted-wire pairs (TWP). However, the presence of twisting provokes an alteration of the wave propagation parameters of the wire pair itself. The periodicity arising from conductor twisting gives rise to frequency-domain standing-wave effects that may dramatically alter the system propagation properties as compared to those concerned with the untwisted case. This paper deals with the analysis of the propagation properties of a three-conductor nonuniform transmission-line system comprising a TWP running above a conducting plane. In particular, we show that important stop bands with anomalous dispersion characteristics occur for frequencies such that the twist period gets close to one half wavelength. A simplified abrupt-twist model for the TWP, together with an averaging technique, is used in order to derive closed-form analytical results for the wave propagation parameters of the three-conductor system. This model, despite its simplicity, conveys the key ideas necessary for a good understanding of the propagation properties of the helical-type TWP configuration.     

Transient stability limit issues at three-phase short-circuit in parallel running of both a superconducting generator and a conventional one

Experimental studies using20-kVA superconducting generators (SCG) have been performed in an attempt to understand some of the characteristics of SCG in power systems. It is necessary to investigate the characteristics for the parallel operations of both an SCG and a conventional generator (CG) when an SCG is installed in a present power station. Some of the results of the authors' studies on parallel running of the 20-kVA SCG and the 20-kVA CG are described in this paper. In the experimental system, the SCG is connected to a regional power system (infinite bus) through reactors (artificial transmission lines) and the CG is connected to the terminal of the SCG. Using experiments and computer simulations, the transient characteristics at three-phase short-circuit faults are investigated: 1) when the CG is not disconnected; and 2) when the CG is disconnected after reclosing the line with the fault cleared. Two kinds of stable limit curves are obtained for output power at three-phase short-circuit fault for the aforementioned two cases.     

小电流接地电网改进能量法接地选线原理

根据小电流接地电网单相接地故障时电压电流的变化特点,利用中性点电压、故障相电压和零序电流构造的能量曲线的斜率来进行故障选线.该方法不受电网平衡情况和接地电阻大小的影响,对复杂的间歇性电弧接地故障同样有效.MATLAB仿真证明了本文的结论是正确的.     

Eddy currents generated in an elliptic conductor by a transverse alternating magnetic field

Contents The eddy currents generated in an elliptic conductor by a transverse alternating uniform magnetic field are investigated by using the Bubnov-Galerkin method. By digital computations the graphs of the power losses caused by these currents are traced. Moreover, a way of construction of complete sequences is given for the case when the norms of the metric coefficients reciprocals are finite.

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Die durch das Wechselmagnetfeld in einem elliptischen Leiter induzierten Wirbelströme

Übersicht Die durch das Wechselmagnetfeld in einem elliptischen Leiter induzierten Wirbelströme werden mit der Bubnov-Galerkin-Methode untersucht. Man hat die durch numerische Berechnungen ermittelten Diagramme bearbeitet, die die Leitungsverluste darstellen. Außerdem hat man eine Herangehensweise zur Schaffung der vollständigen Folgen angegeben, für den Fall, in dem die Normen der Inversen der Metrikkoeffizienten endlich sind.

     

Calculation of the impedance of a conductor with an elliptic cross section in the slot of an electric machine

Contents A method of calculation the impedance of conductors in electric machine slots is presented. The calculations have made for conductors with elliptic cross section. The Bubnow-Galerkin method has been used for the calculations and the accuracy of the results obtained has been evaluated on the basis of published data.

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Berechnung der Impedanz eines Massivleiters in einer elliptischen Nut

Übersicht Die Arbeit behandelt die Methode der Berechnung der Impedanz von Leitern, die in der Nut einer elektrischen Maschine eingebettet sind. Die Berechnung wurde für einen Leiter elliptischen Querschnittes durchgeführt. Die Genauigkeit der erhaltenen Ergebnisse wurde durch Vergleich mit der Fachliteratur kontrolliert.

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Symbols A z-component of vector potential (complex rms value) - B _t ,B tangential components of induction - complex value of current, |I|-rms value - imaginary unit - Z complex impedance - |z|,z ^* modulus of complex numberz, complex conjugate ofz - Rez real part of complex numberz - Imz imaginary part of complex numberz - magnetic permeability - conductivity - pulsation - ² scalar Laplacian - ₁ angle of slot opening - l conductor length - 2a, 2b major and minor axis of ellipse - c distance of focus from center of ellipse - cross-section area - S boundary of area - R resistance - X reactance     

Earthing impedance of cylindrical conductor in a two-layer soil

Contents The paper deals with the determination of the earthing impedance of a cylindrical electrode modelling an earthing system of a transmission tower. Assuming a soil of two layers, the effect of the eddy currents in the soil is investigated with the conductivity and the thickness of the layers varied. The solution of the Helmholtz equation given for the magnetic field intensity is obtained by a global variation method. The satisfaction of Dirichlet boundary conditions on the surface of earth and along thez-axis as well as of the continuity conditions on the interface of the layers is ensured with the aid ofR-functions.

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Bestimmung der Erdausbreitungsimpedanz von zylindrischen Elektroden

Übersicht Die Arbeit beschäftigt sich mit der Bestimmung Erdausbreitungsimpedanz von zylindrischen Elektroden. Im Fall von aus zwei Schichten bestehendem Erdboden wird die Abhängigkeit der Wirkung der Wirbelströme von der spezifischen Leitfähigkeit bzw. von der Schichtdicke untersucht. Die Lösung der Helmholtz'schen Differentialgleichung, die die magnetische Feldstärke beschreibt, erfolgt durch die Globalelementmethode der Variationsrechnung. Die Erfüllung der Dirichlet'schen Randbedingungen an der Oberfläche der Erde und entlang derz-Achse, sowie die Erfüllung der Kontinuitätsbedingungen an den Schichtgrenzen ist durch die Anwendung derR-Funktionen gesichert.

     

小电流接地系统经过渡电阻接地的分析

对小电流接地系统单相经过渡电阻接地后三相对地电压、中性点对地电压的变化进行分析 ,并对绝缘监察系统的灵敏度及非故障相对地电压大于 3倍相电压的范围和最大值作了分析     

Analytical formula of induced electric fields in a spherical conductor by an ELF dipole magnetic field source

An analytical formula of induced electric field E in a spherical conductor by an ELF dipole magnetic field source is mathematically derived in vector form based on the equivalent mutlipole moment method with reexpansion technique (RE‐EMMM), where M _‖ and are parallel and perpendicular components of M , respectively. The validity of the formula is confirmed in the following three ways: (i) the derivation of the formula from the Sarvas equation with the reciprocity theorem derived by Eaton; (ii) the convergence of the formula to that of homogeneous magnetic field when M _‖ is located at the infinite distance; (iii) comparison of the analytical solutions with numerical solutions by RE‐EMMM. Furthermore, a formula for the trajectory, which satisfies E = 0 , is derived for the field by M _‖. © 2008 Wiley Periodicals, Inc. Electr Eng Jpn, 166(3): 8– 17, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20739