As a kind of flexible transmission equipment

the thyristor controlled series compensator(TCSC)is used to improve transmission capacity. The existing reliability model of TCSC seldom considers its components

such as capacitor bank and reactor

thus the impact of components' availability on power system reliability cannot be analytically quantified. According to the failure modes of the components

hierarchical reliability equivalence is proposed to derive the state space model for the series compensated line. With the improved frequency and duration(F&D)method

the state probabilities and transition rates and their sensitivity to the component's availability are quantified. Finally

the sensitivity of system indices to the series compensated line

and sensitivity of the line to the TCSC components

are combined to yield the reliability decomposition model of the power system reliability to the TCSC components. A numerical analysis has validated the feasibility and accuracy of the model proposed which is conducive to finding and improving the vulnerable components of the flexible transmission equipment from the viewpoint of power system operations. This work is supported by National Natural Science Foundation of China(No. 51277049).