中文摘要：

直流输电系统在系统调试或故障情况下会处于单极大地回路运行方式，这时地中直流会对交流系统的正常运行带来不利影响。为此全面总结了我国龙政、天广、三广直流输电线路在调试与运行过程中对附近交流电网运行带来的噪声、谐波、振动等不利影响；通过贵广调试现场实验及对实测数据的详细分析，归纳得到变压器中性点直流、谐波、噪声等与入地直流之间的关系规律；通过建立理论模型，对于地中直流的分布特性进行了分析，并以春城变电站为例就中性点直流电流进行了计算。计算结果验证了所提理论模型和计算方法的有效性。

英文摘要：

The HVDC transmission system may be operated in ground return mode when the system is in debug or failure. The disadvantages, such as audible noise, harmonic and oscillation of the transformer in AC systems, are illustrated by analyzing the data of LONG-ZHENG, TIAN GUANG and SAN-GUANG HVDC system. And field experiments were implemented by measuring the neutral DC current of more than ten transformers when the GUI GUANG HVDC system was in debugging. Some useful data were acquired and some interesting results were obtained by analyzing these data. Based on the field-circuit theory model, the DC ground current flowing through the neutral point of the transformer was analyzed, and the result verified the feasibility of the theoretical model.