Calculation of Thyristor Reliability Parameter of UHVDC Converter Valve in HEMP Environment

The threat of HEMP (high altitude nuclear electromagnetic pulse) in power system has emerged significant to be assessed. The thyristor converter valve is the core equipment in UHVDC (ultra-high voltage direct current) transmission system, and to evaluate its reliability in HEMP environment is quite 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. This paper proposed a modeling method for the calculation of failure rate of thyristor. First, the wideband model of key components as well as stray capacitances in the converter valve is built based on impedance measurement. Second, thermal impedance model of thyristor is built, and the model parameters are calculated according to the transient thermal impedance curve of the device. Based on the models above, the electrical and thermal stresses of thyristor are obtained and analyzed. Finally, the reliability model of thyristor is established, and the parameter failure rate is calculated which could be used in the further study of converter valve reliability. The quantitative analysis is presented in the paper.