I don't really know the source anymore, but I had the same question
during my Bachelorthesis and found some formulas in an old dissertation
about transformers.
If modelled as a PI-equivalent circuit you have:
ohmic resistance: The (rated) ohmic resistance is equivalent to the real
part of the rated short circuit voltage u_k.
-> u_k = sqrt[(u_r)^2) + (u_x)^2]. Usually u_k and u_r are given (u_x
is often very small, so it is omitted in most cases).
inductance: Same here with the imaginary component u_x.
capacitance: sqrt(i_l^2 - P_fe/S_r)
conductance: P_fe/S_r
i_l is the relative "Leerlaufstrom" (I can't think of a decent
translation, but Leerlauf is the contrary of short circuit and strom
means current).
P_fe is the real Power loss due to the iron core.
S_r is the rated apparent Power of the transformer.
I hope this is not too confusing, because my technical englisch is not
the best.
Oliver, wenn du möchtest, kann ich dir das Ganze auch noch mal auf
Deutsch schreiben.
greetings
Simon Schneider
Am 09.02.2012 17:20, schrieb Ray Zimmerman:
I am not a transformer modeling expert, but I'll do my best to answer
your first two questions ...
1) The resistances are modeled in p.u. based on the system baseMVA and
the baseKV at the "to" side of the transformer.
2) They are modeled on the "to" side of the transformer, which could
be attached to the high or low voltage side.
3) This one I don't know the answer to.
--
Ray Zimmerman
Senior Research Associate
419A Warren Hall, Cornell University, Ithaca, NY 14853
phone: (607) 255-9645
On Feb 9, 2012, at 10:30 AM, Oliver Lösch wrote:
Hi alltogether,
I’ve got the following three questions regarding transformator
modeling in Matpower:
1)The series equivalence resistances are modeled in the casefiles
just as the lines are but by also adjusting the calculation of the
p.u. units of the resistances corresponding to the transformators
ratio – is this correct?
2)All the resistances etc. are modeled on the low voltage side of the
transformator – correct?
3)And how can the equivalence resistances coming from the iron losses
and the main inductivity be modeled in the casefiles?
I do very much appreciate all kinds of helpful answers!
Best regards
Oliver Loesch
