1.Key Laboratory of Control of Power Transmission and Conversion, Ministry of Education (Shanghai Jiao Tong University), Shanghai 200240, China;2.State Grid Hubei Electric Power Co., Ltd., Wuhan 430077, China

DC line protection is the key to the development of multi-terminal flexible DC transmission technology. The boundary conditions provided by DC current limiting reactors facilitate the design of fault protection algorithms. Combining the voltage drop characteristics of the current limiting reactor with the shunt characteristics of adjacent lines, a protection scheme for multi-terminal flexible DC lines based on boundary transient energy is proposed. The protection scheme uses the difference of the transient energy ratio between the two ends of the line to identify internal and external faults, and uses the transient energy ratio of positive and negative poles to select the fault poles. The implementation of the protection scheme is simple, the data of the two terminals does not need to be synchronized, and the operation time is short. The simulation results show that the scheme can reliably identify faults and select fault poles in different fault scenarios, and has strong endurance to transition resistance and strong anti-noise ability. This work is supported by National Natural Science Foundation of China （No. 51877135），National Key R&D Program of China （No. 2016YFB0900601）， and Shanghai Rising-Star Program （No. 18QA1402100）.