Influence of the AC system faults on HVDC system and recommendations for improvement

The interaction between AC and DC systems in a long distance bulk power transmission system is very complicated. In this paper, taking some cases in China Southern Power Grid as examples, the main functions of the DC control system operating during the AC faults is discussed. During the AC faults, the protection and monitoring system for DC converter and the protection system for converter transformers and auxiliary transformers may work incorrectly, reasons for these cases are analyzed and recommendations are given to solve the defects. Experience from these cases will help us to improve the ability of operation and maintenance to insure the safety and provide useful references for the design of HVDC and the coordination of AC/DC system in China.