中文摘要：

士800kV特高压直流输电单极一大地回路方式运行时强大的入地电流将对接地极周边环境及交流电网造成很大影响。针对随着四川大规模交直流电网的建设，交流变电站和直流输电接地极选址的矛盾日益突出的问题，根据±500kV直流输电工程的运行经验，结合具体极址资料和假定交流电网模型，采用经典镜像法和数值积分法分析计算了接地极对周边交流电网的影响范围。计算结果表明：流入交流系统的电流值，不仅与变电站间的地理位置及直线距离有关，同时与交流电力系统的网络接线及其参数等因素有关；±800kV直流接地极当其额定工作电流为4000A时，在选址时应至少对其周边20km范围内进行影响评估，作为新建换流站或≥110kV电压等级交流变电站，最好在距离接地极60km以外选择。

英文摘要：

The working current of !800 kV Ultra High Voltage Direct Current transmission project （UHVDC） is over 4000 A. This high current will cause great influence to the AC Network around the grounding electrode when the UHVDC trnsmission operates under monopolar mode, especially in Sichuan Province where its AC and DC systerns are being developed so fast. So it is important to evaluate the environmental influence brought about by the earth current effectively to the AC system. Based on the running ±500 kV direct current projects in China and the concrete data of electrode site and assumed model of AC network, the scope of influence brought about by the grounding electrode to the AC system has been calculated by image and numerical methods. The results show that 1 ） the DC current which is lowing into the AC network is not only related to the geographical position and linear distance between substations, but also correlative to the network connection and parameters of the AC power system.2） it is best to evaluate the environmental influence of DC grounding electrode rated ±800 kV within the scope radius of 20 km while the electricity of the electrode is 4000 A. As to the sites of newly built converter stations or AC transformer stations rated 110 kV and above, they are best to be chose at 60 km away from the DC grounding electrode.