Transformer Impedances
Transformer Impedances
(OP)
Hi Everyone,
Perhaps I a bit rusty but in any case here is my situation:
I am trying to complete a generation interconnection data sheet for submission. I have a project that will be using a 27/230 kV step-up transformer. It will be rated at 150 MVA. Now, given that the client has actually NEVER built anything like this I am stuck with providing impedances on something that doesn't yet exist. The simplest way to do this (I think) is to hit a WECC load flow case and find something that is close in voltage class and MVA capacity. OK, done, no problem. I have a per unit R and X.
Now, it has been a looonnng time--how do I convert these per unit quantities into things like winding resistance? I know how to take a per unit X and turn it into percent impedance, but I am somewhat uncertain on how winding resistance shakes out. Any advice?
Thanks!
Perhaps I a bit rusty but in any case here is my situation:
I am trying to complete a generation interconnection data sheet for submission. I have a project that will be using a 27/230 kV step-up transformer. It will be rated at 150 MVA. Now, given that the client has actually NEVER built anything like this I am stuck with providing impedances on something that doesn't yet exist. The simplest way to do this (I think) is to hit a WECC load flow case and find something that is close in voltage class and MVA capacity. OK, done, no problem. I have a per unit R and X.
Now, it has been a looonnng time--how do I convert these per unit quantities into things like winding resistance? I know how to take a per unit X and turn it into percent impedance, but I am somewhat uncertain on how winding resistance shakes out. Any advice?
Thanks!






RE: Transformer Impedances
What, precisely, have you gotten from the WECC load flow case? Per unit R and X of what?
RE: Transformer Impedances
Primary Winding (i.e. H Winding):
Winding Resistance in ohms
Impedance in Percent
MVA Base
Tested Taps
Secondary Winding (i.e. X Winding):
Winding Resistance in ohms
Impedance in Percent
MVA Base
Tested Taps
The actual data sheet to be filled out is available at the following URL:
http://www
I am thinking about using that R, X, and B in per unit quantities from a WECC load flow case and then calculate the ohmic values from those. R=0.0380, X=0.12837, and B=0 for a 150 MVA 230/25 kV transformer on a 100 MVA system base. The CAISO staff is of little help on what they really mean in regards to tested taps--I probably haven't found my way to the right person yet.
I am not really a transformer person but rather a plannig engineer--load flow and transient stability studies. I suppose I have been spoiled by having these numbers provided for so long, I mean does anyone actually have winding resistances of transformers available off of the top of their heads? I figure the answer was always as low as possible.
Anyway, hopefully this will enable someone to re-educate me...
Thanks again!
RE: Transformer Impedances