Thanks for the replies !
I take your point about the insulation levels for autotransformers, and it is an issue we're looking into with the manufacturer.
I also take the points made in jwerthman's last paragraph. However, our studies show that the reduction of fault current from the 'T' branch...
In order to limit 110kV single phase fault levels it has been suggested to employ impedance in the neutral of 250MVA 220kV/110kV autotransformers (wye-connected with a delta tertiary). To 'spec' the neutral impedance do i have to give a fault current level (say full-load of the auto) and a fault...
