Why do you need a withdrawable VT?
To replace the fuse without deenergizing the bus.

Eitherway Withdrawable VT or Fixed VT, one has to open the VT compartment to do the maintenance or replace the VT fuse?
In this process, the door is opened, so during the time the door is open, the operator is in risk to Arc flash exposure.
According to IEC 62271-200, IAC is not tested when the VT door is open
For withdrawable VT, you can bring the VT to withdrawable position with the door closed
as the VT is coming to the withdrawable position the shutter that connects the VT to the line bus bar gets closed

When the VT shutters are closed but the VT is in withdrawable position and now you open the door of the PT; At this stage is the IAC (Internal Arc classification) of the switchgear still valid? or not?