Analysis of DC Line Fault Characteristics with the UHVDC Hierarchical Integration into AC Power Grid

The hierarchica multi infeed structure of UHVDC lincreases the complexity of the system structure, the interaction between UHVDC systems, the coupling between UHVDC and UHVDC systems, and so on. It puts forward new requirements for the relay protection of HVDC systems. Therefore, it is of great significance to analyze the change of fault characteristics after UHV connected to power grid. In order to analyze the fault characteristics of HVDC line under the framework of UHVDC hierarchical integration into AC power grid, this paper first analyzes the basic framework of UHVDC integration into AC power grid. On this basis, the fault characteristics of DC lines in the region, out of the region, high transition resistance grounding fault and bipolar operation mode are analyzed. Finally, the simulation analysis of various DC line fault characteristics verifies the correctness of the analysis.