You were right, thanks a lot! Earlier I did not modify the b columns of the branch matrix. Using Y_base = 1/ Z_base the powerflow results stay the same no matter which baseMVA value I chose.
-- Dipl.-Inform. Thole Klingenberg OFFIS FuE Bereich Energie | R&D Division Energy Escherweg 2 – 26121 Oldenburg – Germany Fon: +49 441 9722-732 E-Mail: [email protected] URL: http://www.offis.de Von: Thole Klingenberg <[email protected]> An: "MATPOWER discussion forum" <[email protected]> Datum: 29.04.2011 15:38 Betreff: Re: Re: Question on baseMVA Gesendet von: [email protected] Hi, thanks for your help. I am not sure if I can follow, though. 1) The formula you have posted implies that the results of the power flow analysis change if the base voltage is modified. It seems to me, that this is not the case in Matpower. Changing the base voltages in "case9.m" from 345 to 200 or some other value and then executing 'runpf' yields exactly the same results as the case without modifications does. 2) I tried to adjust the r and x columns of the branch data according to your formula (kVAnew=100, kVAgiven=1000 ==> Znew (pu)= 0.1 * Zgiven(pu) ) The results of runpf do still differ from the original results Von: [email protected] An: "MATPOWER discussion forum" <[email protected]> Datum: 29.04.2011 14:40 Betreff: Re: Question on baseMVA Gesendet von: [email protected] > Hi, I have a question about Matpower 4.0 > > By running" runpf('case9') " I get the power flow of the 9-bus system. > If I change baseMVA from 100 to 1000 or 10 in file 'case9.m', > the results of power flow do change completely! Why? > Is this because the r, x and b columns are expressed by p.u.-values? > If so, how do I have to transform them in order to receive the same > results as before? How do I choose a baseMVA value for an unknown > System? > Thanks very much > Well, If you want to change your MVA base and/or voltage base, all the pu impedances must be changed accordingly by: Znew(pu) = Zgiven(pu)((KVgiven/kVnew)^2)(kVAnew/kVAgiven) I hope it helps. Prof. J.R. Camacho UFU - School of Electrical Engineering Uberlandia - MG - Brazil [email protected]
