直流输电系统出口回路复杂，存在硬接线和各种现场总线混用的问题。基于对已投运的直流输电工程的分析，分别探讨了早期直流输电工程、近期直流输电工程和采用现场总线直流输电工程的直流出口回路及其存在的问题，并提出了改进方案。

The outlet circuits of HVDC system are complicated and exist such problems as the hard wiring and fieldbus are blended together. Based on the analysis of the HVDC transmission systems in operation, this paper discussed the outlet circuits of three kinds of HVDC transmission systems, which is the early HVDC transmission system, the short-term HVDC transmission system and HVDC transmission system with fieldbus, and put forward some operational improving suggestions.