Suspended discharge is one of the typical defects of GIS. Through the detection and analysis of partial discharge（PD）

the state evaluation and fault diagnosis of GIS equipments can be realized. In this paper

pulse current method and decomposition detection method are used

in order to explore the characteristics of PD process and its decomposition products of GIS suspended defect model

which under discontinuous constant voltages. And after the SF

6

gas decomposition reaction during PD process

the diffusion characteristics of SO

2

CO and H2 S gas are explored. The experimental results show that: although th

e applied constant voltage interrupted

the PD characteristic did not change. Along with the PD process

SF

6

gas moisture content is increasing

but there is a limit that equipment damp is inferred only by the high moisture content of the SF

6

gas in GIS. If only SO

2

gas is detected in the decomposition gas test

it is perhaps that a kind of serious suspended discharge defects may exist in GIS;CO gas diffusion rate is faster than others

so it can be used as a target gas to judge the severity failure of GIS.