Preventive maintenance (PM) enhances the reliability of an ultra-high-voltage DC (UHVDC) line. However

it introduces new states and complicates the task of determining the reliability parameters of the component with PM. The hierarchical connection (HC) of the inverter improves the flexibility of UHVDC

but the state spaces of the inverter and UHVDC-HC are determined by capacity distribution between the high terminal (HT) and low terminal (LT)

which has not been studied yet. In this paper

the reliability of UHVDC-HC with the PM is studied. First

with the impact of PM described by a nonlinear coefficient

the state space of the components with PM is aggregated. It is the same size as without PM. The only difference is the transition rate. Second

considering power distribution between the HT/LT and its dependence on the state of the rectifier

new capacity levels of HT/LT

e.g.

75%/2

50%/3

are defined. Third

with capacity levels of the HT/LT differentiated

2 existing reliability indices are extended

and 2 are newly defined. Finally

a sensitivity model of the reliability of the UHVDC-HC to its parameters and the PM period is proposed.