For identifying the diffusion characteristics of the characteristic gas SO

2

F

2

in GIL

which is generated by the decomposition of SF6 discharge

and its influence

on gas component detection result

the different degree of defects

time t and SO

2

F

2

volume fraction at the defect place and the place at 1.5 m far from the defect are measured respectively by the GIS scale model and diffusion test platform. Combined with Fick’s law

the diffusion process of SO

2

F

2

in SF6 is simulated. The results show that the formation rate and discharge strength of SO

2

F

2

at the defect position has a definite linear relation and shows non-linear increase at weak discharge and linear increase at strong discharge. The SO

2

F

2

volume fraction at the two positions has a definite time delay and attenuation

but the difference of increase form of the volume fraction is small. The diffusion process of SO

2

F

2

in GIL is mainly related to the time t

position x and diffusion coefficient DSO

2

F

2

/S/SF6. However

the formation rate of SO

2

F

2

does not affect the diffusion speed. During the diffusion period

the larger the x is

the larger the diffusion time delay Δt of SO

2

F

2

is

and CSO

2

F

2

attenuates exponentially with the increase of x

but the increase rate of CSO

2

F

2

does not generate remarkable variation during the diffusion period. Therefore

for GIL equipment

the CSO

2

F

2

at the defects position would be much higher than the actual detection results. The influence of the diffusion shall be considered when CSO

2

F

2

is taken as the diagnosis criteria. While

the influence of the diffusion on the increase rate of CSO

2

F

2

is less and is more suitable to be used as the diagnosis basis for the insulation status of GIL.