Under the condition of unbalanced economic progress and geographical distribution of natural resources in China

high voltage direct current (HVDC) transmission is playing a more and more important role in energy saving

emission reduction

and optimization of resource allocation. To steadily improve the reliability of the operating HVDC systems and provide a full view of the operating HVDC conditions in State Grid Corporation of China (SGCC)

this paper takes the HVDC systems

ultra high voltage direct current (UHVDC) systems and back-to-back HVDC systems as the research objects

and a statistical analysis is made of the forced outages using the yearly operation data. An assessment is made of the systems’ operating conditions from the perspective of the extreme weather

equipment fault

and external damages. By referring to typical case studies of faults

the security situation the SGCC is in is made clear. The weak links in the systems available are analyzed and relevant suggestions are made.