In the operation of UHV multi-terminal hybrid DC project

the third station needs to be on-line switched on/off. Under the current technological conditions

the on-line switching on/off of the third station can be achieved by the coordination of the direct current high-speed parallel switch (HSS) and VSC-HVDC converter valve. Due to the relative weak DC curret breaking capacity and withstanding voltage ability across open conatcts of the HSS

it is therefore necessary to analyze the key characteristics of on-line switching on/off of the third station of multi-terminal hybrid DC project based on DC high-speed parallel switch. In his paper

such key electrical performances as the DC current breaking ability

arcing withstand ability cross open contacts of HSS uncer various conditions are analyzed based on ±800 kV Kunliulong VSC-HVDC transmission project. With Liuzhou station as an example

the on-line switching on/off strategy

including the switchign on

switchign off and premanent fault pole isolation of the third station. is analyzed and the logic coordination requirement between the HSS and the control system is propsoed

which provides a reference for formulating online switching on/off strategy and the control system and HSS coordiantion strategy for UHV multi terminal hybrid DC project.