External insulation is one of the critical aspects in the HVDC equipments and converter station design. Especially for UHVDC converter stations, the long creepage and clearance required has significant impact on the equipment and station design. The external insulation design of DC yard, valve hall, and for converter valves is presented. It is the intention of this report to review and summarize the work that has been done and the decisions that have been taken to the benefit of further work and design of new projects.

Over the last 20 years, HVDC has become the dominating technology for long-distance transmission of bulk power. The use of 800 kV HVAC, which was introduced in several countries during the 1960s and 1970s, has largely come to a halt (9). The rapid development and increased confidence in HVDC technology have encouraged the transition from AC to DC. This is apparent in China for bulk power transmissions. This paper will cover the classic thyristor-based HVDC technology. The newer HVDC Light TM technique, for lower powers (up to ≈350 MW), is not covered.