Analysis of Commutation Failure Principle and Protection Logic in LCC High-Voltage Direct Current Transmission Systems

High-voltage direct current (HVDC) transmission systems offer longer transmission distances and greater transmission capacities, making them an important transmission method in the future. However, when commutation failure occurs in an HVDC system, it can lead to DC current surges and temporary power interruptions, severely threatening the safe and stable operation of the AC-DC system. Therefore, this paper focuses on the commutation failure faults in HVDC transmission systems, analyzes the causes of commutation failure, and divides the commutation process within one power frequency cycle into five stages for detailed examination. It also analyzes the criteria for commutation failure protection, the conditions for protection blocking, and the outcomes of protection actions. Finally, by analyzing the actual fault waveforms from a converter station, the paper identifies the reasons for the commutation failure through the examination of the control and protection systems.