HV access isolation requirements for GIS

[spartanv12]

Can anyone advise what HV isolation requirements are being used for access to HV GIS switchgear ?
We have 110KV GIS switchgear with a 3 position bus isolator that can either be open, closed or in earth position on the non-bus side.
When in the earth position the earth point is a removable copper bar that is also used as a test point for primary injection etc.
Is this a suitable isolation point, considering the 110KV is only 4 inches away through SF6 gas and we will have to remove the earth bar ? I've had a verbal from our engineering and standards section saying that yeah she'll be right!!

Regards.

 

[cuky2000]

To have an idea of dielectric clearance for 110 kV in SF6 medium, see the enclose graph. Clearance in SF6 pressurized at one bar is around 3/4 inches.

Considering higher pressure in the GIS vessel, 4" provide reasonable safety clearance assuming surge arresters limit any overvoltage in the system.