Hi, Cusu First you should define, where do you like evaluate? transmission or distribution system. If you are studyng transmission system you can neglect r of transfomers and lines, by other hand, if you evaluate distribution system you can´t not do it, because values are hight. For transformers you can neglet primary and secondary resistances include Gm (core losses), Xm is approximated by a constant value. This formula x= u_k x (U^2/S) represent short circuit impedance (Rt=0,1 Xt), where u_k equivalent 5 to 10% Un. Generally this apply for test of transformers for determine impedance in primary or secondary, if you like determine Zp short circuit secondary and measure Z in that winding, and the same to other side. If you study asimetrical components in transformers X1=X2=X0, meant these impedances in all sequences are equivalents. Conexion group is important specially in zero sequences where interview type of conexion, for example Yy, Yd, Dd, Yny0d, and others. In line transmissions are differents, X1=X2 and X0=2 or 3 times X1. Is important take account in transmssion line its lenghts (medium or long), manufacture give values of resistance, reactances and capacitance of lines, these values you should work in per unit values. I advice this book to review of parameters of transmissin lines: Aluminium Electrical Conductor Handbook
Best regards. From: [email protected] To: [email protected] Subject: RE: Help with modelling a transformer & TAP Date: Thu, 30 Aug 2012 13:57:04 +0200 I have one remaining question, if you please. How do I define the r,x, and b value for a branch in which you have a transformer? I can imagine that for the x value one would use the formula x= u_k x (U^2/S) , for the b value Y=1/Z=1/(r+jx)=g+jb and then take the b value. But how do i identify r? I just know the formulas for a transformer to identify the copper and iron losses. But what about BR_X in this case? Regards, Cansu > Subject: Re: Help with modelling a transformer & TAP > From: [email protected] > Date: Wed, 29 Aug 2012 20:39:34 +0200 > To: [email protected] > > Alright, thanks a lot once again! Now I should be able to model tap > transformers as well! > > Regards, > > Cansu > > > > On 29.08.2012, at 20:30, "Carlos Murillo" <[email protected]> wrote: > > > Yes, although the default value of 0 (meaning no tap switching capability) > > actually means a 1.0 tap, that is, a nominal ratio. > > > > carlos. > > > > On Wed, Aug 29, 2012 at 2:26 PM, Cansu Yildirim <[email protected]> > > wrote: > >> Thank you very much for your quick answer Carlos! > >> > >> So in my case, since I have just a normal transformer, this would mean > >> that the tap parameter is zero right? > >> > >> Regards, > >> > >> Cansu > >> > >> > >> > >> On 29.08.2012, at 19:57, "Carlos Murillo" <[email protected]> > >> wrote: > >> > >>> Matpower uses the one line network representation in the per unit > >>> system. One of the main ideas behind the per unit system is to get rid > >>> of all the transformers and instead represent all voltages normalized > >>> to the nominal voltage of the branch/bus in question. Variable tap > >>> transformers are special transformers that can be tapped at points off > >>> the nominal ratio. That is what the tap parameter represents; it does > >>> not represent the turns ratio of the transformer. Please refer to any > >>> textbook on power systems to see how the per unit system is employed. > >>> > >>> carlos. > >>> > >>> On Wed, Aug 29, 2012 at 1:09 PM, Cansu Yildirim <[email protected]> > >>> wrote: > >>>> Hello, > >>>> > >>>> I'm currently trying to get familiar with matpower. I have following > >>>> problem > >>>> with the 'transformer off nominal ratio'. > >>>> > >>>> I need to model a transformer. The values given are following one: > >>>> > >>>> U1: 20 kV > >>>> U2: 0.4 kV > >>>> rated power: 400 kVA > >>>> no load losses: 0.61 > >>>> no load current (%): 0.1525 > >>>> u_k: 3.85 > >>>> Cu losses: 4.6 kW > >>>> switching group: Dy5 > >>>> > >>>> I have following questions: > >>>> > >>>> 1) how do I calculate the TAP? When I look into the casefiles, I can see > >>>> that the value fpr the tap is most time between 0.8 and 1.5 > >>>> I would have calculated by dividing 20kV/0.4KV=25 which does not seem > >>>> to be the correct value for the tap. > >>>> > >>>> 2) How do I identify the BR_X and BR_B ? When I look into the equivalent > >>>> circuit diagram I know that there are more components that need to be > >>>> calculated. So what > >>>> do these parameters mean for the transformer? > >>>> > >>>> I would be grateful for any help. > >>>> > >>>> > >>>> Kind regards, > >>>> > >>>> > >>>> Cansu Yildirim > >>>> > >>>> > >>> > >> > >> > > > >
