椭圆环布置的垂直型直流接地极的溢流特性

椭圆环布置的垂直型直流接地极占地面积小,地形适应能力强,具有推广应用价值,但椭圆环布置带来的溢流不均匀特性值得深入研究。分析并对比接地极外形尺寸对溢流特性的影响,外形参数包括椭圆率、极环周长、电极长度、电极间距、电极数量。研究表明,椭圆率越大、电极长度越长、电极间距越小、电极数量越少,则电极之间的不均匀程度也越高;且影响程度最大的是椭圆率,其次是电极长度和电极间距,再次是电极数量。采用椭圆环布置垂直接地极时,需要考虑电极之间和单个电极本身的两类溢流不均匀特性的叠加,以控制任一点上的最大溢流密度偏差系数。     

A Method for Reducing Grounding Impedance

This paper investigates grounding impedance reduction with various shapes of grounding electrodes in comparison with a conventional vertical rod based on field measurements and FDTD simulations. It is found that a vertical rectangular conducting plate is effective for reducing the transient and steady‐state impedance to less than half that of the vertical rod. A circular conducting plate parallel to the earth surface is also effective in reducing the steady‐state impedance, but the transient impedance is nearly the same as that of the vertical rod. The rate of reduction is proportional in some way to the surface area of the electrode, but tends to saturate as the area increases. The transient impedance is rather independent of the earth resistivity and permittivity, but tends to be inversely proportional to the wavefront duration of the applied current. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 185(1): 27–35, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22405     

高压架空避雷线对接地网接地阻抗测量结果的影响研究

与接地网相连的高压架空避雷线对接地网接地阻抗的测量结果有较大影响，且解开避雷线后的接地阻抗测量结果均比解开前的大。章介绍了直线0．618法和四极法2种测量方法及其接线原理，并具体介绍了百丈涤水力发电厂一、二级站之间110kVT型接线的架空避雷线对一、二级站接地网接地阻抗测量的影响情况。     

基于脉冲功率技术的高压电场感应取能设计

针对电力巡线旋翼无人机续航能力不足的问题,提出一种基于脉冲功率技术的高压电场感应取能设计。以巡线无人机机载导体作为悬浮电极,在电力线与架空地线之间高压电场中储存感应电能,级联气体自触发开关和电感,并与架空地线构成取能回路,悬浮电极击穿开关气隙对地放电。随气隙放电发展,悬浮电极与电力线、架空地线间分布电容将迅速分压,抑制放电,使气隙间无法形成电弧,而转为高频流注脉冲放电,激发回路高频电磁振荡,通过电磁互感实现电场感应电能输出。文中详细介绍了脉冲功率电场感应取能设计及抑制放电原理,分析取能等效电路并建立了放电脉冲取能模型,在实验室环境下进行物理平台搭建与测试,实验结果证明设计可行。     

吉林电网一次调频分析

针对东北调度通信中心对东北电网三省区间联络线功率交换控制性能考核由A标准过度到控制性能标准(CPS),以东北电网2次全网一次调频试验为基础,对吉林电网机组一次调频情况进行了分析,指出了目前机组在一次调频测试、大修、煤质、频率差及投入方式等方面存在的问题,提出了进一步提高调频投入率;建设基于EMS的一次调频监视考核系统;实现对并网发电厂一、二次调频工作的考核和补偿等建议。     

Novel measurement system for grounding impedance of substation

In order to measure the grounding impedance of a grounding system more precisely and easily, two key problems of the measurement system: the location of the voltage electrode and the elimination of the noise and interference must be conquered. The new theoretical analysis and measurement system of the grounding impedance based on short-current lead wire and a swept frequency ac source is proposed. The compensating position of the voltage electrode to obtain the real grounding impedance is evaluated by analyzing the soil structure, the grounding system under test, and the position of the current electrode. This new system measures the ground impedance at several frequencies other than power frequency, then interpolates them to acquire the ground impedance at the power frequency. The mutual inductance between the potential and current wires is analyzed and eliminated. The industrial computer-based grounding impedance measurement system is developed and the analysis software is programmed. A field test was performed and compared with the traditional method in the substation and the novel system worked well.     

非圆截面接地体的等效半径研究

现有接地计算均将接地体视为圆柱导体,而工程中大量使用扁钢、角钢等非圆截面材料。总结了各种接地体半径等效方法,利用有限元计算软件,建立了扁形、角形、圆形等典型横截面接地体的计算模型,基于接地体对地电阻相等原则确定其等效半径。进一步分析等效半径下接地体的纵向内自阻抗,确定接地体相应的等效电阻率和相对磁导率。最后,研究各种等效方法对接地网工频接地阻抗计算结果的影响。研究发现,各种工程近似等效方法中,利用截面周长相等法获得的扁钢接地体等效半径进行接地网的计算能够保证足够的准确性。     

On the influence of conductor heights and lossy ground in multi-conductor transmission lines for lightning interaction studies in railway overhead traction systems

Railway overhead traction system is a classic example of scattered conductor configuration, where tracks and other wires form multi-conductor transmission lines (MTLs) with large variation in conductor heights above ground and they are spread across regions having different soil conditions. Lightning transient analysis in such systems has not received much attention earlier. Here we analyze the influence of conductor heights and lossy ground on the induced voltages in a two conductor MTLs for the case of a direct lightning strike. For transient analysis, modified time domain transient ground impedance expressions having better early and late time behavior was used. The dependence of transient ground impedance on conductor heights and ground resistivity are presented and discussed. The early time transient ground impedances are unaffected by ground resistivity but their decaying nature is highly dominated by ground resistivity. It is found, if one of the conductors is close to ground (a rail) and if it is at large vertical distance from struck conductor (an auxiliary power line), then with increasing ground resistivity the peak induced voltages in the conductor close to ground initially increase, then decrease and finally tend to remain constant (within 100–10,000 Ω m). This phenomenon is opposite to that compared to conductors that are close to each other with minimum vertical separation (two auxiliary power lines), where the peak induced voltages increase with increasing ground resistivity. The study focuses mainly to access when a mutual coupling due to system geometry or due to ground losses becomes dominant in determining induced effects from lightning in MTLs, which could be an important contribution to the lightning interaction studies for electrified railway systems.     

输电线路杆塔接地电阻的简化计算

输电线路杆塔接地设计中,通常应用经验公式计算杆塔接地电阻,计算精度有限.为此,考虑到接地导体扩散电流的不均匀性,对接地导体进行分段处理,计算各分段导体的自电阻系数和互电阻系数,进而求得接地导体的接地电阻.可根据精度要求确定分段数量,分段数量越多,计算精度越高.最后分析了输电线路杆塔常用的射线接地体、双环形接地体分别在不...     

单根伸长接地体的冲击特性与仿真模型的研究

冲击接地阻抗是影响输电线路防雷等级和雷击跳闸率的重要因素。目前,通常采用模拟试验或者仿真计算来研究冲击接地阻抗,无法真实反映接地体冲击接地特性。为了研究接地体在冲击电流下的特性,本文采用大型冲击电流发生器对接地体进行真型试验研究,以多种型式接地体为研究对象,讨论了冲击电流幅值和接地极尺寸对接地体冲击特性的影响并建立了接地体冲击接地阻抗EMTP仿真模型。试验结果表明,冲击电流幅值升高、接地体长度增加或截面直径增大都会使冲击接地阻抗降低,且接地体长度和冲击电流幅值的影响均出现饱和现象;仿真结果表明,通过分段π型等值电路Models模型建立的接地体冲击接地阻抗仿真模型可有效计算接地体冲击接地阻抗。     

Mutual coupling between horizontal earth return conductors usingactual routing parameters

A formula for calculating mutual coupling between diversely routed, horizontal earth-return conductors that measure grounding system impedance is derived by using the complex ground plane concept used to approximate the Carson equation. Each potential conductor section is approximated with equal-length segments that parallel one of the current conductor sections. By repeating the parallel segmentation of each potential conductor section with each subsequent current conductor section and summing the segment mutuals, overall mutual couplings between diversely routed conductors is obtained. This process is useful for calculating mutual to the potential conductor and for comparing possible potential conductor routings so as to minimize the overall mutual coupling     

分层土壤结构变电站接地阻抗测试信号的处理

正确测量变电站的真实接地阻抗是确保变电站安全稳定运行的基本保证 ,而测量时测试信号的正确处理是获得真实接地阻抗的关键。本文通过分析接地电阻测量信号的组成 ,提出了综合采用数字模拟方法进行信号处理 ,去除干扰的方法 ;另外通过采用等效复穿透深度法计算水平分层土壤时电压和电流测量引线间的互感 ,此方法能有效消除引线间感应电压对测量结果的影响。本文根据层状土壤的电磁场理论推导得到了水平层状土壤结构的复穿透深度。该方法在某50 0kV变电站的接地阻抗测试中进行了实际应用 ,如果不考虑测量引线间的互感 ,在本文的实例中可导致接地阻抗增加 7 3% ,影响是比较大的。本文提出的方法可为电力部门提供参考。     

特高压双回路GIL感应电压电流计算分析

气体绝缘线路(GIL)回路间电磁感应关系不同于架空导线,线路中存在GIL将会影响感应电压、电流的计算结果,从而影响线路地刀的选型。文中以同塔双回架空线和GIL混合特高压线路为例,研究回路间电磁感应的计算。首先对GIL进行电气参数计算,并理论推导混合线路感应电压、电流计算公式;其次利用EMTP-ATP仿真验证理论分析结果,分别仿真研究了GIL在母线位置、在线路中间以及不含GIL 3种工况下的感应电压、电流变化规律,并分析了GIL在线路中间时感应电流大幅度增加的原因;最后研究了GIL在线路中长度占比的不同对感应电压、电流的影响。研究结果可为含GIL的混合线路地刀选型提供理论计算参考。     

Finite element analysis of a floating microstimulator.

Analytical solutions for voltage fields in a volume conductor are available only for ideal electrodes with radially symmetric contacts and infinitely extending substrates. Practical electrodes for neural stimulation may have asymmetric contacts and finite substrate dimensions and hence deviate from the ideal geometries. For instance, it needs to be determined if the analytical solutions are adequate for simulations of narrow shank electrodes where the substrate width is comparable to the size of the contacts. As an extension to this problem, a "floating" stimulator can be envisioned where the substrate would be finite in all directions. The question then becomes how small this floating stimulator can be made before its stimulation strength is compromised by the decrease in the medium impedance between the contacts as the contacts are approaching each other. We used finite element modeling to solve the voltage and current profiles generated by these radially asymmetric electrode geometries in a volume conductor. The simulation results suggest that both the substrate size and the bipolar contact separation influence the voltage field when these parameters are as small as a few times the contact size. Both of these effects are larger for increasing elevations from the contact surface, and even stronger for floating electrodes (finite substrate in all directions) than the shank-type electrodes. Location of the contacts on the floating electrode also plays a role in determining the voltage field. The voltage field for any device size and current, and any specific resistance of the volume conductor can be predicted from these results so long as the aspect ratios are preserved.     

引外接地对降低接地网接地阻抗的作用分析

引外接地是一种降低地网接地阻抗的有效措施。文中分析了接地网的有效外引长度确定、接地网大小与外引接地有效长度的关系、连接导体半径与引外接地效果的关系等,为引外接地的科学设计和施工提供了依据。     

冲击电流下接地极屏蔽效应的试验研究(英文)

Generally,the flow of a lightning impulse current from a grounding electrode into ground is a very complicated process determined by many factors.In order to analyze the mechanism of the impulse current dissipating in the earth from grounding electrode,the experiments that had been carried out by other authors almost used a single horizontal grounding wire or vertical grounding rod for sake of simplicity.However,in practical conditions,most of the grounding systems are constructed of grounding electrodes with branches in different directions.In this study,basing on the principle of dimensional similarity,impulse simulation experiments are performed on the common ground electrodes with conductor branches.This paper focuses on analyzing the impulse current dispersal regularity of different branches when injecting at one point.Comparing with the leakage current distribution of a single ground electrode,it is found that the leakage currents along the branches increase with the distance to the current feed point,and the more conductors near the injection point,the more uneven the leakage current distribution is.This work indicates that shielding effect should be taken into account when analyzing the impulse characteristics of grounding electrodes.     

垂直型直流接地极散流特性试验研究

垂直型直流接地极占地面积小,能将电流导入地底深处,有利于改善跨步电压和接触电势,对环境影响小,是一种可行的新型直流接地极布置方式,但垂直型接地极存在散流分布不均匀的问题。用接近实际工程的方法埋设了3根垂直型直流接地极,并注入直流电流,模拟接地极真实运行环境,对其散流特性、电流分配、接地电阻、跨步电势和利用系数进行了测量。试验表明,接地极散流不均匀,下部散流大于上部,且存在明显的端部效应,但由于其将电流导入地底深处,有效地改善了跨步电势;多根并联接地极间的电流分配受接地极之间的屏蔽作用和接地极接地电阻的共同影响;试验测得的利用系数与理论计算值具有较高的吻合程度,验证了理论计算方法的准确性。     

电位降法测量接地电阻时电流极引线长度的影响

讨论了电流极引线长度对变电站接地电阻测量误差的影响,分析得到了不同土壤结构所要求的电流极引线长度。采用反向法测量接地电阻时,测量得到的接地电阻比真实接地电阻要小,但可将反向法测量得到的接地电阻作为变电站接地电阻测量值的下限。采用全球定位系统(global positioning system,GPS)确定测量电极与接地网之间的距离后,能够根据电位降法比较准确地测量接地电阻。实际测量结果表明,如果电流极引线过短,可通过辅助分析的方法得到实际接地电阻的电压极补偿点位置。     

基于模量网络分析的接地极线路故障定位新算法

针对直流接地极线路发生远距离、高阻接地故障时,现有故障定位算法精度低的问题,提出了一种基于模量网络分析的接地极线路故障定位新算法。基于线路的分布参数模型,建立了故障后接地极线路故障模量网络,在此基础上利用接地极线路量测端的电压、电流量计算沿线的电压、电流分布,进而得到故障点处的测量阻抗,根据故障点处测量阻抗虚部最小的特点进行故障定位。大量仿真结果表明,该算法可实现接地极线路全长范围内的准确定位,且不受故障位置和分布电容的影响,具有较高的故障定位精度。     

分层土壤短距离放线下接地电阻测试方法研究

当土壤不均匀,如土壤为双层甚至三层时,采用传统补偿法测量接地电阻往往会带来较大测量误差。研究提出了短距离放线方式下接地电阻测试方法。分析了工频接地电阻与电流注入点的位置关系,研究了不同电流注入点对接地电阻测量偏差的影响规律,验证了短电流极引线法在工频接地阻抗测试中的可行性。针对不同的土壤结构,研究了电流引线布线长度对电压补偿点位置的影响。提出不同土壤结构下电流引线长度的选取规律,实现了短电流引线下接地阻抗的准确测量。