The importance of HVDC project in power system gradually appears. With the continuous increase of project operation life

its reliability in normal environment and extreme environment deserves further study. The reliability evaluation of the thyristor converter valve

as the core equipment in HVDC transmission system

appear to be particular important. The failure rate of thyristor is the critical parameter for the overall reliability evaluation

while its value varies depending on the electrical and thermal stress conditions. In this paper

a modeling method for calculating the failure rate of thyristor based on stress analysis is presented. Firstly

the broadband model of the key elements and stray capacitance of the converter is established. Secondly

the electrical stress distribution of different regional components in the converter valve is simulated and analyzed. Then the thermal impedance model of the thyristor is established and the thermal stress of the corresponding thyristor is analyzed. Finally

the reliability model of thyristor is established

and the reliability parameter failure rate of the corresponding thyristor is calculated

which provides the basis for quantitative analysis for further study of the reliability of the converter valve.