An Improved Algorithm of Grounding Grids Corrosion Diagnosis Based on Total Least Square Method

A new model considering corrosion property for grounding grids diagnosis is proposed,which provides reference solutions of ambiguous branches.The constraint total least square method based on singular value decomposition is adopted to improve the effectiveness of grounding grids' diagnosis algorithm.The improvement can weaken the influence of the model's error,which results from the differences between design paper and actual grid.Its influence on touch and step voltages caused by the interior resistance of conductors is taken into account.Simulation results show the validity of this approach.

Comparative Analysis of Equal and Unequal Grounding Grid Configurations by Compression Ratio and Least Square Curve Fitting Techniques

The primary aim of the power system grounding is to safeguard the person and satisfying the performance of the power systemtomaintain reliable operation.With equal conductor spacing grounding grid design,the distribution of the current in the grid is not uniform.Hence,unequal grid conductor span in which grid conductors are concentrated more at the periphery is safer to practice than equal spacing.This paper presents the comparative analysis of two novel techniques that create unequal spacing among the grid conductors:the least-square curve fitting technique and the compression ratio techniquewith equal grid configuration for both square and rectangular grids.Particle Swarm Optimization(PSO)is adopted for finding out one optimal feasible solution among many feasible solutions of equal grid configuration for both square and rectangular grids.Comparative analysis is also carried out between square and rectangular grids using the least square curve fitting technique as it results in only one unequal grid configuration.Simulation results are obtained by theMATLAB software developed.Percentage of improvement in ground potential rise,step voltage,touch voltage,and grid resistancewith variation in compression ratios are plotted.

Research on Magnetically Coupled Resonant Detection Method for Breakpoint of Four Mesh Grounding Grid

Magnetically coupled resonant technology is a novel method for solving the breakpoint locating of power grounding grid.But the method can only detect breakpoints of a single mesh grounding grid at present.In this paper,a magnetically coupled resonant detection method for four-hole grounding grid breakpoint is proposed.Firstly,the equivalent circuit model of the four mesh grounding grid with two types of breakpoints,namely edge branch and intermediate branch,is established.The input impedance and phase angle of the system are obtained by analyzing the equivalent capacitance and equivalent resistance in the model.Secondly,the magnetically coupled resonant physical process of grounding grid faults is solved via HFSS software.The magnetic field intensity and phase frequency characteristic curves of four mesh holes with different branches and positions of breakpoints and different corrosion degrees are studied,and an experimental system is built to verify the feasibility.The results show that under the condition of grounding grid buried depth of 0.5 m and input frequency of 1~15MHz,and there is an inverse relationship between equivalent capacitance and distortion frequency,the phase angle is positively correlated with the degree of corrosion of grounding grid,and the error of signal distortion frequency can be positioned at 5%.This paper provides some ideas for the application of magnetic coupling grounding grid detection technology.

An Investigation into Substation Grounding and Its Implementation on Gaza Substation

An investigation into the optimal design of a substation grounding system for the transmission substation in Gaza City, Palestine has been carried out. A research into the most influential parameters on the effectiveness of the substation grid system has been performed and its results have been incorporated into the Gaza case study. Through modelling and simulating the power station in Gaza while considering some field data, an optimal substation grounding grid has been designed and has shown complete conformance to safety. It is thus considered that such a design will protect personnel in any area of the substation in addition to the installed machinery if the largest possible fault current was to traverse the earth.

Grounding Locations Assessment of Practical Power System

Grounding Points (GPs) are installed in electrical power system to drive protective devices and accomplish the person nel safety. The general grounding problem is to find the optimal locations of these points so that the security and reli ability of power system can be improved. This paper presents a practical approach to find the optimal location of GPs based on the ratios of zero sequence reactance with positive sequence reactance (X0/X1), zero sequence resistance with positive sequence reactance (R0/X1) and Ground Fault Factor (GFF). The optimal values of these indicators were deter-mined by considering several scenarios of fault disturbances such as single line to ground on a selected area of the Iraqi National Grid (132 KV) taking into account the statue of GPs for transformers in the other substations. From the presented results in this paper, it is noted that GFF calculated for some substations could be used to measure the effectiveness of GPs. However, the operated time of relay can be taken as a criterion of this measurement for selecting the best location of GPs.

Axisymmetric alternating direction explicit scheme for efficient coupled simulation of hydro-mechanical interaction in geotechnical engineering-Application to circular footing and deep tunnel in saturated ground

Explicit solution techniques have been widely used in geotechnical engineering for simulating the coupled hydro-mechanical(H-M) interaction of fluid flow and deformation induced by structures built above and under saturated ground, i.e. circular footing and deep tunnel. However, the technique is only conditionally stable and requires small time steps, portending its inefficiency for simulating large-scale H-M problems. To improve its efficiency, the unconditionally stable alternating direction explicit(ADE)scheme could be used to solve the flow problem. The standard ADE scheme, however, is only moderately accurate and is restricted to uniform grids and plane strain flow conditions. This paper aims to remove these drawbacks by developing a novel high-order ADE scheme capable of solving flow problems in nonuniform grids and under axisymmetric conditions. The new scheme is derived by performing a fourthorder finite difference(FD) approximation to the spatial derivatives of the axisymmetric fluid-diffusion equation in a non-uniform grid configuration. The implicit Crank-Nicolson technique is then applied to the resulting approximation, and the subsequent equation is split into two alternating direction sweeps,giving rise to a new axisymmetric ADE scheme. The pore pressure solutions from the new scheme are then sequentially coupled with an existing geomechanical simulator in the computer code fast Lagrangian analysis of continua(FLAC). This coupling procedure is called the sequentially-explicit coupling technique based on the fourth-order axisymmetric ADE scheme or SEA-4-AXI. Application of SEA-4-AXI for solving axisymmetric consolidation of a circular footing and of advancing tunnel in deep saturated ground shows that SEA-4-AXI reduces computer runtime up to 42%-50% that of FLAC’s basic scheme without numerical instability. In addition, it produces high numerical accuracy of the H-M solutions with average percentage difference of only 0.5%-1.8%.

Establishment and analysis of global gridded Tm-Ts relationship model

In ground-based GPS meteorology, Tm is a key parameter to calculate the conversion factor that can convert the zenith wet delay（ZWD） to precipitable water vapor（PWV）. It is generally acknowledged that Tm is in an approximate linear relationship with surface temperature Ts, and the relationship presents regional variation. This paper employed sliding average method to calculate correlation coefficients and linear regression coefficients between Tm and Ts at every 2°× 2.5° grid point using Ts data from European Centre for Medium-Range Weather Forecasts（ECMWF） and Tm data from ＂GGOS Atmosphere＂, yielding the grid and bilinear interpolation-based Tm Grid model. Tested by Tm and Ts grid data, Constellation Observation System of Meteorology, Ionosphere, and Climate（COSMIC） data and radiosonde data, the Tm Grid model shows a higher accuracy relative to the Bevis Tm-Ts relationship which is widely used nowadays. The Tm Grid model will be of certain practical value in high-precision PWV calculation.

Study on Lightning Transient Ground Potential in the Chaoyang Mountain Wind Farm

In order to get the distribution characteristics of lightning transient ground potential of 100 MW wind farm in the Chaoyang Mountain,Jinzhai County,the characteristics of lightning parameters within 5 km of the wind farm were analyzed based on the lightning monitoring data from 2006 to 2020 provided by Anhui Meteorological Bureau.According to the on-site geological investigation,a double-ring ground network model was established to simulate the three-dimensional transient contact voltage and step voltage distribution of a typical wind fan was obtained through simulation.The results show that the average lightning current amplitude around the wind farm was 44 kA,instead of 10 kA in the current traditional simulation research,which is used as the excitation source for the subsequent simulation of lightning transient ground potential.The peak value of lightning transient contact voltage of the single wind turbine is 2158.35 V,and the peak value of lightning transient step voltage is 441.75 V.The simulation results can provide certain reference for subsequent lightning risk assessment,lightning scheme design and ground grid construction of wind farms.

Analysis on the Effect of Shading on the Characteristics of Large-scale on-grid PV System in China

Because of rich solar resource and low land cost, a lot of large-scale ground-based grid-connected PV systems have been built in Northwest China. In this paper, some shading phenomena on a grid-connected PV system inNorthwest Chinaare classified and analyzed. Through the I-V curve test of PV modules, it can be seen that dust influence system performance of the grid-connected PV system. And the experimental results have shown that shading could affect the electrical properties of PV modules. Meanwhile, same shading area on different shading positions could have different impacts on the identical PV module.

强震损伤格栅墙处理地基抗液化性能离心模型试验研究

水泥土格栅墙能有效减缓被围束土体在地震作用下的剪切荷载及变形,已广泛应用为一种高效的抗液化对策。针对其长期服役过程,开展了两组超重力离心模型试验以研究强振历史对水泥土格栅墙内被围束土体液化响应的影响。两组模型均由15 m厚的易液化含黏粒砂土和2.5 m厚的粗砂层组成。其中,一组模型采用水泥土格栅墙对易液化层进行加固;另一组模型则未进行处理,作为自由场地对照组。两组模型均经历振幅为0.15g的振动事件,且在0.15g振动事件前,对两组模型施加振幅为0.4g的振动事件作为强振历史。试验结果表明,格栅墙在强振下主要的损伤模式表现为竖向贯穿型裂缝,并部分伴随有局部斜向裂缝,且外侧格室对于中心格室表现出类似于群桩基础的“遮蔽效应”。强振历史后,格栅墙中心格室内被围束土体的超静孔压显著低于自由场地,损伤后格栅墙仍具有良好的抗液化效果。同时,格栅墙由于强振后整体刚度的削弱,其与下卧粗砂层间的剪切变形显著减小。

基于单端分支系数的四端柔直环网线路保护方案

为提升直流线路保护在柔性直流环网中的速动性与可靠性,提出一种基于单端分支系数的保护方案。分析了不同故障位置下各换流阀提供的故障电流分量,并根据单端换流阀极线电流突变量构造分支系数,结果表明线路保护区内故障下的单端分支系数小于区外故障,利用该特征构造区内、外故障识别元件。在线路高阻接地致使主保护失效时,根据桥臂最大允许电流决定线路纵联后备保护的开放时限,以优化现有主、后备保护方案之间的时序配合方案,保障各种直流线路故障工况下,换流阀不间断运行。保护方案不依赖线路边界元件,算法简单,大量仿真结果表明,该方案有良好的耐受过渡电阻能力,能在换流阀闭锁前实现故障区域可靠识别。

基于空间网格划分的地杂波建模新方法

雷达型空空导弹具有全天候、全空域作战能力,具有较强的低空下视能力。在导弹下视攻击时,地面多普勒杂波会影响导引头对真实目标的检测。针对高重频脉冲多普勒雷达导引头,提出了一种基于空间网格划分建立地杂波模型的新方法,以天线波束指向为中心,围绕天线主瓣在三维空间划分网格,之后计算投影到地面的网格面积,根据雷达方程建立回波信号模型。通过理论推导,给出了影响地杂波强度的主要因素,包括导弹距地面高度、导引头波束擦地角和地面反射率等。最后通过建立数字仿真模型验证了方法的正确性。该方法可以在保证杂波形态一样的同时减少仿真时间。

石墨烯/三聚磷酸铝水性导电防腐涂料的制备及性能研究

以石墨烯为导电填料,三聚磷酸铝为防腐填料,水性环氧树脂作为黏结骨料,配置得出了一种用在接地电极表面的导电防腐涂料。通过附着力、导电性以及耐蚀性测试,再结合土壤模拟浸泡试验,研究不同石墨烯与三聚磷酸配比对涂层导电与防腐性能的影响,结果表明当m(G)∶m(EP)=17%,m(ATP)∶m(EP)=1%时涂层表现出了优异的导电性与抗腐蚀性,可以满足电力接地网使用要求。

变电站周围管网及新建地网系统对原接地网特性参数的影响

“双碳”目标的大背景下,随着以高比例新能源为主体的新型电力系统的建设,原变电站接地网已然难以满足当下需求,存在着新改造地网与老旧地网的安全运行问题以及周围地下金属管网的接入使改造地网产生的参数变动问题。接地网的某项参数不达标,则会影响变电站和站内设备的稳定运行,对人身安全造成严重的影响。因此,需要分析改建地网及金属管网等原变电站周围管网系统参数指标的安全限值,综合考虑分层土壤结构、地下金属管网及其他周围地形对于改建地网安全运行的影响效应。基于矩量法并结合CDEGS接地网仿真软件搭建了新旧地网以及周边金属管道数学模型,综合考虑各种土壤特性下变电站周围金属管道以及新建地网对原变电站的各个特性参数,进行了分析研究,获得了多种情况下变电站接地网与金属管道以及原接地网与新建地网之间的阻性耦合影响曲线及各项接地参数的对比,并据此提出相应的防护措施。实验发现:对金属管道敷设绝缘层可以有效减小管道的散流作用,但对降低接触电压并不明显,敷设绝缘层前后接触电压仅下降3%;将新建地网与原接地网相连使原变电站接地网最大接触电压下降28.1%,降阻率达20%。为变电站接地网改造工程及新型电力系统的构建提供一定的理论依据。

面向环保接地施工的杆塔分支式外延接地网接地特性研究

低碳环保已成为国家的战略和政策导向,输电杆塔在降阻施工时,常采用敷设长距离外延接地极方式接地,造成资源浪费、环境破坏等问题。针对杆塔接地施工环境的复杂性与施工面积的有限性,文中提出输电线路杆塔分支式外延接地网散流降阻结构,实现了接地降阻施工的低碳环保。首先,仿真计算单根外延接地极的有效降阻长度;然后,研究了土壤电阻率、入地电流频率对单分支式和多分支式外延接地网降阻特性的影响规律;最后,分析了不平衡分支式外延接地网的散流特性。结果表明:相比于传统方框带射线型接地网,分支接地极结构比例为1/3的单分支式外延接地网具备更好的降阻特性,并且三分支式外延接地网的接地施工面积更小,不平衡分支式外延接地网有助于进一步降低主接地网的散流密度。

基于凝聚层次聚类的接地网定向支路减维腐蚀诊断优化方法

为了更有效地对接地网水平支路导体的腐蚀故障情况进行诊断,采用模型仿真方法对基于电网络理论的接地网腐蚀诊断方法进行分析,针对现有接地网腐蚀诊断模型存在的缺陷,提出了一种基于凝聚层次聚类的接地网定向支路减维腐蚀诊断优化方法。该方法通过分析恒定直流激励下接地网各支路电阻变化对于端口的灵敏度规律,利用支路端口灵敏度对接地网可及端口进行凝聚层次聚类,以选出最优端口测量组合;然后采用定向支路减维方法对各端口电阻方程进行支路筛选,将灵敏度低于判定阈值的导体支路划为未知支路,高于判定阈值的导体支路划为健康支路,以降低腐蚀诊断模型的病态程度和计算维度。在某模拟变电站接地网上对该方法进行了仿真验证,结果显示优化后的整体诊断相对误差仅为3.07%,远小于普通接地网腐蚀诊断的6.74%,证明该方法能显著提高接地网腐蚀诊断精度,可为接地网腐蚀诊断提供理论指导。

一种柔性接地线状态指示装置的设计与应用

提出了一种采用快速磁场检测方法的柔性接地线状态快速指示装置,并给出了其详细的设计和应用方法。在所设计的柔性接地线状态快速指示装置中,状态检测单元利用微型三维磁场实现实时高速磁场监测,状态报警单元通过3个阈值实现局部声光报警,而无线信号发送单元实现状态信息云显示。实验结果表明,所提出的柔性接地线状态快速指示装置可以有效地实现对接地线电流的智能监测,从而避免了接地装置误挂和接地不良造成的检修事故。

220kV变压器中压侧中性点经小电抗接地的运行分析

北京电网分区运行,其中枢纽站的接地方式关系整个电网运行,K分区中的A变电站采用220 kV变压器中压侧中性点经小电抗接地的运行方式。分析了该分区的主变中性点接地情况、A变电站的等值网络,同时计算了A变电站的短路容量、不同主变并列运行时的单相短路电流,计算表明,中性点经小电抗接地后可降低其单相短路电流,满足设备热稳定性要求。同时提出中性点小电抗投运后对现场运行、倒闸操作的要求。

Corrosion behavior of low-carbon Cr micro-alloyed steel for grounding grids in simulated acidic soil

To improve the corrosion resistance of steels for grounding grids, a low-carbon Cr micro-alloyed steel was developed （C 1 steel）, and corrosion behavior of Q235 steel and newly developed C1 steel in simulated acidic soil was investigated. The corrosion rate was evaluated with the mass loss measurements, while the corrosion morphology of surface and cross section of rust layer was observed by scanning electron microscopy. The corrosion products were analyzed by energy- dispersive X-ray spectrometry, X-ray diffraction and X-ray photoelectron spectroscopy, and the polarization curve was measured using potentiodynamic polarization method. Results indicated that C 1 steel displayed good corrosion resistance in the simulated acidic soil, of which the corrosion rate was only 30% of that of Q235 steel after corrosion for 360 h. The analysis of rust layer showed that lower carbon content in steel could reduce the tendency of micro cell corrosion and appropriate amount of chromium could improve the corrosion potential of metal matrix. Moreover, the analysis of X-ray photoelectron spectroscopy revealed that the chromium enriched in inner rust layer of C1 steel existed mainly in the form of Fe2CrO4, which facilitated the formation of Cr-goethite and improved the protection of corrosion products.

构网型储能应用于电压暂降治理的研究

为缓解电压暂降现象导致的生产可靠性问题,提出了构网型储能主动支撑电压的解决思路。首先分析电压暂降的电气特征参数,建立构网型储能控制模型。同时,对比常规跟网型储能与构网型储能在系统电压扰动时的暂态响应特性,得出构网型储能的电压源属性在维持内电势稳定上的控制优势。通过PowerFactoryDigsilent仿真平台进行建模,模拟石化企业内外部电网典型运行方式。对比故障条件下,构网储能接入及其接入点差异对系统电压的抬升效果。结果表明,构网型储能可以在电压暂降情况下瞬时输出无功功率,显著提高三相接地故障下的系统电压,最高可达540%。对于单相接地故障,构网储能也有明显改善作用,特别是储能接入石化C变与石化B变35kV母线时,电压可抬升18.7%和15.3%,避免设备受电压暂降影响。