The generally accepted practice for earthing a network fed from a transformer Delta connection is to use a zig-zag transformer. This will provide a neutral point which can be connected to earth and provide a low impedance path for earth fault currents. I have recently come across some substations in which a Star/Star transformer has been used with the primary star point earthed to provide the earthed neutral point for the MV network. When I look at this arrangement it seems to me that this will provide a high impedance path for earth fault current as there is no flux balance in the core of the earthing transformer. Am I wrong in this assumption? (I would be happy to be wrong on this one). Has anyone come across this arrangement using a Star connected transformer for earthing a Delta system?


thanks

Geoff