在高压直流接地极工程中,加装均流电阻是改善地表电位分布,降低极址跨步电压的一种有效手段.然而,由于土壤电阻率分布的复杂性和各向差异性,采用理想的水平分层模型计算配置直流接地极的均流电阻往往存在较大的误差.针对此问题,文中提出了 一种基于接地极特性参数实测值的均流电阻配置方法.该方法通过实际测量接地极极环各段的分流比例、接地电阻、互阻、自跨步电压系数、互跨步电压系数等参数,以此作为输入条件,将各段的跨步电压相等作为控制目标,计算获得均流电阻的配置方案.最后通过一个缩比接地极模型,对均流电阻配置方法及过程进行了模拟试验.试验表明,加装均流电阻后,场区的最大跨步电压降低了 31％,效果显著,验证了均流电阻对降低跨步电压的有效性.

In order to master the safety of the GIL shell grounding system of the 1000kV AC UHV GIL tunnel project and support the design and construction of the project, a shell grounding system model consisting of the main grounding grid of connection stations on both sides, the tower grounding grid of overhead ground wires on both sides and the tunnel grounding grid is established. The GIL current and potential distribution under normal operation and short-circuit fault are calculated, and the influence and setting of grounding poles and three-phase connection poles are analyzed. The results show that: under normal operation, the current of connection poles and grounding poles along the GIL presents a U-shaped distribution. In case of short-circuit fault, besides the two ends, the current of the connection poles and grounding poles near the fault point also presents a peak, which can reach hundreds of amperes; and the distribution of potential and potential difference along the GIL also presents a similar U-shaped feature. The spacing of grounding poles can be set within 300m, which can ensure that the potential difference is within the safety limit. The copper bar of 50mm×5mm can be selected for both the grounding pole and the intermediate connecting pole, and the conductor with larger cross section is needed for the connection pole at both ends due to the long-term passing current close to the rated value.

为了研究异性导电媒质对直流接地极跨步电压分布的影响,通过CDEGS建立水平双圆环直流接地极模型,计算极址外部附近以及极址区域内存在异性导电媒质时的跨步电压分布.结果表明:当接地极极址外部附近存在一块高(低)电阻率的异性媒质时,将会使外环靠近异性媒质区域的溢流密度及跨步电压下降(升高);当极址内部的表层局部区域存在一块高(低)电阻率的异性媒质时,将会使位于异性导电媒质的环段的溢流密度下降(升高),但跨步电压却反而增加(降低);当极址内部的下层局部区域存在一块高(低)电阻率的异性媒质时,将会使位于异性导电媒质的环段的溢流密度和跨步电压同时降低(升高).研究成果可为直流输电工程中接地极设计及选址提供参考.

为研究土壤特性对特高压直流接地极跨步电压分布的影响,采用CDEGS软件建立了双圆环直流接地极仿真模型,对比分析了不同土壤特性下双圆环直流接地极上方跨步电压分布规律.计算结果表明:在均匀土壤中,双圆环直流接地极上方跨步电压随着土壤电阻率的增大而升高;在水平双层土壤中,表层土壤电阻率的变化对双圆环直流接地极上方跨步电压分布影响较为显著,当表层土壤超过一定厚度后,表层土壤厚度的变化对双圆环直流接地极上方跨步电压影响较小.

直流输电无接地极运行有助于尽早实现双极送电,换流站接地网替代直流接地极是目前最有效的措施.换流站接地网替代直流接地极情况下可能存在人身和二次设备安全问题、变压器直流偏磁危害、接地网发热和腐蚀问题.论文对这些问题进行逐一分析,最后综合各影响因素提出了直流输电控制策略的要求,即单极故障联跳双极、不平衡电流控制和双极同步解闭锁.研究工作为直流输电新型的无接地极运行方式提供了有效参考,相关控制策略在南方电网普侨特高压直流输电工程中得到了良好的应用.

为研究杆塔接地装置的冲击特性,准确掌握其雷电响应,设计了冲击大电流试验系统.在分析冲击电流发生器原理的基础上,计算放电回路的电气参数,并提出分布式冲击大电流试验系统.该系统由4台十字型对称分布的电流发生器组成,可在负载4 Ω的情况下产生峰值100 kA、波形为8/20 μs的标准雷电流.并选择典型的杆塔接地装置检验了该试验系统的试验能力.试验结果表明:在单级电容充电电压为185 kV情况下,产生波形7.64/18.45 μs、峰值100.358 kA的冲击电流,设计方案是有效可行的;接地装置的冲击接地电阻随着冲击电流幅值增大而减小.

In order to analyze the temperature characteristics of horizontal grounding electrode,the electric thermal dynamical coupling model of a 9mhorizontal grounding electrode is integrated to simulate its transient temperature rise with ANSYS software.And then it obtains distribution law of transient temperature field and temperature rise curves.Comparison of calculation and test results show that the current divergence and temperature distribution of horizontal grounding electrode present obvious end effect,which vary in a U-shape manner;the ends of horizontal grounding electrode get the highest value rapidly.The influence of coke bed section on transient temperature field in grounding electrode is simulated and it shows that the temperature rise of grounding electrode can significantly decrease by increasing coke bed section,and the highest temperature is in the soil beside coke bed ends.

In order to master the independent grounding performance of the UHV transmission line tower footings, guiding the UHV transmission line grounding design, we investigated the typical structure of UHV tower footings and artificial grounding devices, calculated grounding resistance of various tower footings based on CDEGS, and analyzed various factors. The reduction in resistance of the grounding devices was compared, and potential level and distribution characteristics around the tower in the presence and absence of the grounding devices were simulated. The results show that, most types of tower footings meet the requirements of resistance design when soil resistivity is less than 1 000 Ω·m, most grounding footings cannot meet the requirements of resistance design and need artificial grounding devices or secondary resistance reduction measures when soil resistivity is larger. Artificial grounding devices reduce the max potential rise and the surrounding potential difference. The potential distribution with tower footings cannot meet the touch voltage goal expect the soil resistivity is very small. The simulated error are analyzed by comparing with field measurements, the results show that the modeling method is effective and the simulation deviation is within the allowable range.

In order to study the lightning impulse characteristics of grounding devices, the research on spark effect and inductance effect is taken as the principal line of this paper. Plus the feature of soil discharge, the high frequency response of grounding devices and the change regulation of soil electrical parameters are explored. Furthermore, three transient modeling methods which adopts circuit theory, electromagnetic field theory and dynamic modeling respectively are compared. The development of impulse characteristic tests of grounding devices is also commented. Through summary and analysis of the researches, several important and imperative technical problems needed to be solved and their elementary solutions are presented. The discharge form of soil and the size of discharge area could be approached by collecting soil discharge image by adopting X--ray films or high speed imagers. It is necessary to determine the critical breakdown field--strength and the residual soil resistivity of discharge area which are used in the transient modeling. The spark effect influenced range and the frequency dependence of the spark effect and the inductance effect need to be discriminated. It is suggested to analyze the frequency characteristics of the extensive grounding bodies, the complex structure grounding devices and the grounding devices by adopting the distributed parameters model, the concentrated parameters model and the electromagnetic model respectively. The impulse characteristics of grounding devices which are excited by the impulse current with high amplitude and short front time could be gained by adopting the high voltage and capacity impulse current test systems, and then be used in the field measurement of the impulse grounding resistance.

If DC grounding electrode is near to the transmission corridor, DC current will flow through shielding wires and towers in different equipotentional surface, leading to erosion of the tower. Actual parameters of DC grounding electrode and its nearest AC transmission line of an ±800 kV ultra HVDC transmission project under construction is exmplified , The DC current flowing through each tower and its distribution character were studied . Results showed that the erossion quantity would be more with the increase of the resistivity of the middle earth layer and decrease of the grounding resistance of the tower, and the total erosion is not serious.In the end, some protective measurements are given.

通过对葛南直流输电系统(葛洲坝侧)输送额定容量情况下接地极各种参数的测量,考核接地极的运行状况,并对葛洲坝侧接地极的电气和安全性能进行了评估.