Hi Jean- François,
I think the transformer impedance should be converted to and specified on the base MVA used in the study (mpc.baseMVA). Best regards, russ From: [email protected] [mailto:[email protected]] On Behalf Of Jean-Francois Simon Sent: Monday, August 9, 2021 10:52 AM To: MATPOWER discussion forum Subject: Re: Branches and transformer model Hi Ray, Thank you, I found out there must be 1 at the tap to make Matpower understand the branch as transformer, this is ok, and the impedance in per unit, 14% is 0.14. For example branches: 1 2 0.001 0 0 250 250 250 0 0 1 -360 360; Is a power cable 2 3 0.001 .105 0 250 250 250 1 0 1 -360 360; Is a transformer impedence 10.5% 2 4 0.001 .12 0 250 250 250 1 0 1 -360 360; Is a transformer impedence 12% What I don't understand, as you stated, is where do we specify the transformer MVA rating, which should take part in the calculation except my misunderstanding. For instance both are 16 MVA transformers. So I just set the above values and made a calculation without indicating the transformer apparent power, as I could not find if it matters and where to specify. Regards, Jean-François Le 09/08/2021 à 16:42, Ray Daniel Zimmerman a écrit : Yes, in the current MATPOWER case format v2, the transformers are specified in the same branch matrix as the AC transmission lines. I’m a bit rusty on my transformer modeling, so someone please correct me if I’m wrong, but I believe the % impedance specification is equivalent to the p.u. impedance value expressed using the transformer rated power and voltages as the per-unit bases. So I think you just have to convert the impedance to the system per-unit bases to put it in the branch matrix. Ray On Aug 2, 2021, at 9:49 AM, Jean-Francois Simon <mailto:[email protected]> <[email protected]> wrote: Good day, I am learning MatPower and have a case to study with 8 buses. The below example a simplification: I could understand how to build buses and links and simulate the energy flow. Results look right, however I have a question since the buses are working on different voltage levels, hence some links have power transformers. *** Bus 2: 90 kV - Feeder bus *** *** Bus 3: 30 kV - Load bus *** *** Bus 5: 690 V - Load bus *** <Bus 2>---(90/30kV XFR)---<Bus 3>---(30/.69 kV XFR)---<Bus 5> Bus 2 to bus 3 is a 16 MVA transformer with impedance 10.5% Bus 3 to bus 5 is a 5 MVA transformer with impedance 6.5% At the moment, the bus definition looks like this: mpc.bus = [ 2 3 0.0 0.0 0 0 1 1 0 90.0 1 1.1 0.9; 3 1 7.2 2.1 0 0 1 1 0 30.0 1 1.1 0.9; 5 1 3.5 0.1 0 0 1 1 0 0.69 1 1.1 0.9; ]; And branches definition is incomplete: mpc.branch = [ 2 3 0.1 0 0 250 250 250 0 0 1 -360 360; 3 5 0.1 0 0 250 250 250 0 0 1 -360 360; ]; Is this right transformers are set in "Branches" ? How do we calculate and set resistance branches resistance and and reactance in order to properly integrate transformers as for example in above case ? Thank you for support, Regards, Jean-François Simon
