Yes. On May 14, 2013, at 12:55 AM, Petre Razusi <[email protected]> wrote:
> Thank you Prof. Zimmerman. Your explanations helped me. However, I still have > another thing that is a little bit unclear. > I have some transformer parameters (in Ohms and Siemes) calculated using the > "to" side voltage. How do I convert them to p.u.? Do I use the same Zbase > that you suggested? > > Thank you for your help! > > Petre > > > 2013/5/13 Ray Zimmerman <[email protected]> > Since the branch impedances are on the "to" side of the branch, you are > correct that you would use the voltage base from the "to" bus. > > The formula isn't really a MATPOWER question, so you should be able to find > the answer in a good power systems textbook, however it is very > straightforward to derive yourself. Essentially we want to find the impedance > base (Zbase) in terms of the power and voltage bases (Sbase and Vbase). > > Start with some definitions ... > > (1) V = Vpu * Vbase > (2) S = Spu * Sbase > (3) Z = Zpu * Zbase > > Then some simple relationships ... > > (4) V = I * Z > (5) S = V * conj(I) > > Solving (4) for I and substituting in (5), then solving for Z, gives ... > > (6) Z = |V|^2 / conj(S) > > And we know the p.u. quantities have the same relationships … > > (7) Zpu = |Vpu|^2 / conj(Spu) > > Substituting (1)-(3) and then (7) into (6) and rearranging, gives … > > Zbase = Vbase^2 / Sable > > Hope this helps, > > -- > Ray Zimmerman > Senior Research Associate > 419A Warren Hall, Cornell University, Ithaca, NY 14853 > phone: (607) 255-9645 > > > > > On May 13, 2013, at 3:44 AM, Petre Razusi <[email protected]> wrote: > > > Dear all, > > > > I have some things I don't quite understand regarding the modeling of > > branches and the pu system. > > If I'm not wrong, to transform the R,X and B parameters to pu one needs a > > base impedance. Since the model used for the branch is a complex one, > > dealing with both transformers and lines, I presume that this impedance is > > calculated using the "to" bus voltage. Am I right? And if so, could you > > tell me what is the formula used to compute the base impedance? > > > > Thanks, > > > > Petre > > > > > > >
