Three-winding Trfr Impedance Questions
Three-winding Trfr Impedance Questions
(OP)
A customer has a 3-wdg trfr, 11kV/6.6kV/440V (3MVA/3MVA/100kVA) with vector group 4Dyn11yn11. Primary is delta connected, whilst secondary and tertiary are star connected. Anyone explain what the 4 stands for please?
Nameplate says:
Imp 11kV/6.6kV = 5.37
Imp 11kV/440V = 0.7
Imp 6.6kV/440V = 0.94
a) What would be the MVA base at which these impedances are specified as the nameplate does not say?
b) Can I take it that I can calculate a 3-phase fault at the sec terminals the same way I would a two wdg 11/6.6kV with Z% = 5.37%?
c) Ditto for 3-phase fault at the 440V terminals? Does this mean I have effectively a 11kV/440V trfr with Z% = 0.7? This seems awfully low.
Thanks.
Nameplate says:
Imp 11kV/6.6kV = 5.37
Imp 11kV/440V = 0.7
Imp 6.6kV/440V = 0.94
a) What would be the MVA base at which these impedances are specified as the nameplate does not say?
b) Can I take it that I can calculate a 3-phase fault at the sec terminals the same way I would a two wdg 11/6.6kV with Z% = 5.37%?
c) Ditto for 3-phase fault at the 440V terminals? Does this mean I have effectively a 11kV/440V trfr with Z% = 0.7? This seems awfully low.
Thanks.






RE: Three-winding Trfr Impedance Questions
RE: Three-winding Trfr Impedance Questions
RE: Three-winding Trfr Impedance Questions
RE: Three-winding Trfr Impedance Questions
You would need to solve the impedances as a star connection to do fault level (or voltage regulation) calculations.
Regards
Marmite
RE: Three-winding Trfr Impedance Questions
Thanks.