The operational reliability of ultra-high voltage DC GIL depends on the reliability of the internal insulation design. In addition

such issues as selection of DC current density of conductive element

the positioning design of spring contacts

the treatment of wedge-shaped air gaps at the connection between insulation part and fitting in GIL components as well as the structural design details of support components in the busbar will have a significant influence on the operation reliability of product and cannot be ignored. For UHV DC GIL operating in a very harsh environment

a high airtightness structural design is proposed in this paper in order to assure the reliability of internal insulation work and reduce gas maintenance work. To meet the requirements of low temperature operation at -50 ℃

N

2

/SF

6

gas mixture with very low liquefaction temperature is selected for the product. The ratio

pressure characteristics and insulation characteristics of the two gases are discussed and calculated. The reliability design of the monitoring system for partial discharge

gas density

and micro water conten

t of the product will also affect directly the operational reliability of the product. The research results of the above issues are introduced in this paper

which can be used for the design of high-voltage DC products. A research plan is proposed for such unsolved new technologies as intelligent gas humidity and density monitoring devices based on the principle of cold mirror dew point testing and microelectromechanical technology as well as the initial field strength of partial discharge on the umbrella surface of high-voltage DC composite insulation sleeves. The multiple reliability design points for GIL operation proposed in this paper can be used as reference for other ultra-high voltage DC gas insulated apparatus.