Transformer Zero Sequence Impedance in SKM Powertools 1

[ScottPET]

Can anyone please offer tips in modelling transformer zero sequence impedance of transformers in SKM Powertools. We mostly encounter three-phase delta-grounded wye units, some of which have neutral earthing impedances installed at the star point.

I have seen information stating none should be modelled, other information stating 90% of positive sequence impedance, and yet other information that making it the same as the positive sequence impedance is acceptable.

Thanks

 

[davidbeach]

SKM Powertools allows you to input both (+) and (0) sequence impedances; it uses the (+) for (-) also. The program properly deals with the transformer windings. So the only question is what to use for the (0) sequence impedance. Do a search of this forum for "transformer impedance zero" (without the quotes), there have been many discussions about how zero relates to positive sequence impedance. It depends in part on the transformer configuration and in part on preference of the person entering the data.

 

[ScottPET]

Thanks davidbeach.

After searching the forum and further reading, for most of the transformers we deal with (3 phase Dyn, most likely with core-type cores, i.e. not shell), R0=R1 and X0=(0.85 to 0.9)X1 will be suitable (NER values to be added separately).

Merry Christmas to all.