Research and application of the control and protection strategy for the ±500kV Xiluodu-Guangdong double bipole HVDC project

The ±500kV Xiluodu-Guangdong HVDC system in China is a 6400MW HVDC transmission in double bipole scheme. It is the new HVDC project designed in the scheme of two bipoles with common earth electrode and four DC transmission lines erected on the single tower. In contrast to the traditional bipole HVDC project, this double bipole project obviously has further requirement for the control and protection system. First, a detail research on operating modes is presented in this paper which fulfills both the flexibility and reliability requirements of the double bipole scheme. Then, the well-designed hierarchical configuration of the control and protection system is put forward, as well as the control function configuration which based on this system configuration. A complete backup control concept is introduced in this paper which substantially increases the reliability of the DC transmission. The two bipolar coordinated control strategies and the proper protection strategies are studied carefully and the effective principles are proposed. Some simulation results are presented to confirm the conclusion using the closed-loop simulation system which consists of the real-time digital simulator (RTDS) and the control and protection equipment that applied in site for this project.