Open-line test is one of the most important tests when HVDC station commissioning

during which the valve is easily subject to false protective firing and results in valve block. In this paper

valve false protective firing occurs in Hu-Liao and Qing-Zang HVDC projects is analysed in-depth

with introduction of valve protective firing detection logic and characteristics of open-line test

root cause of false protective firing is presented. It is a valuable experience for subsequent projects commissioning

and can be used to direct the developing of valve control unit with better stability and reliability.