Trfr %Z varaition with size
Trfr %Z varaition with size
(OP)
Hi
I have a 23/11kV, 45/58MVA, delta-star trfr. Z% = 9.8% @45MVA. How do I determine what Z% is at 58MVA? Is there a general formula one can apply to calculate impedances at the different ratings for the same transformer?
Thanks in advance.
Veritas
I have a 23/11kV, 45/58MVA, delta-star trfr. Z% = 9.8% @45MVA. How do I determine what Z% is at 58MVA? Is there a general formula one can apply to calculate impedances at the different ratings for the same transformer?
Thanks in advance.
Veritas






RE: Trfr %Z varaition with size
the % Z at 58 MVA will be 45/58 * 9.8% or about 7.6%.
RE: Trfr %Z varaition with size
RE: Trfr %Z varaition with size
Thanks for that. However, I get that the new impedance is about 12.63% and not 7.6% (58/45 * 9.8%). Zbase = 11.756ohms @45MVA and it is 9.12ohms @58MVA. Thus for a given ohmic impedance the pu impedance must be greater if I express it at 58MVA than 45MVA.
Thanks again.
RE: Trfr %Z varaition with size
You should get the same ohms at both bases.
The 12.63% at 58 MVA is correct.
RE: Trfr %Z varaition with size
Kind regards.