To improve the accuracy of chemical diagnosis method used for estimating the insulation conditions of basin insulators and other epoxy resins solid dielectric in GIS

creeping discharge and related verification tests are set up to study the evolving law of SF6 decomposition products under typical discharge defects on a small apparatus. It is found that COS

as an important characteristic gas related to epoxy resins discharge

is produced under stronger discharge than CS

2

. B3P86/6-31G（d

p）

a method of calculation based on quantum chemistry

is adopted to explore the generating mechanism and energy conditions of COS when partial discharges occur on the solid dielectric

in GIS. Carbon which is a component of COS derives from basin insulators and other epoxy resin solid dielectric

and the reactions of intermediate HCS and O2 as well as CS

2

and OH are two main pathways to generate COS. Experiments and theoretical calculations show that decomposed gas CS

2

has a high sensitivity in judging whether the discharge is related to the epoxy resin solid dielectric

CS

2

can be applied to diagnose faults related to creeping discharge on the epoxy resin. The generation of COS indicates that the discharge level on the epoxy spacer deepens

thus the decomposition products testing period should be shortened

and it is important to strengthen insulation monitoring of relevant GIS chamber.