Hello all! I am carrying out the theoretical (that is, by calculation means) unsymmetrical fault calculations for three winding transformer. It is to my understanding that for the zero sequence impedance for a three winding transformer depends on the winding connections of the generator and the transformer. The case that I'm carrying out now has its three winding transformer - in star earthing for primary and secondary, and delta earthing for tertiary. The generator also has star earthing. In my understanding, the zero sequence impedance of the three winding transformer is now the addition of both Z1 and Z2. is my understanding correct? thanks!