Dear Shuo Chen, I'm used to similar data and calculate r and x as (ur, uk in p.u., base_MVA and S_transformer in MVA): - r = ur * base_MVA / S_transformer - x = sqrt(uk^2 - ur^2) * base_MVA / S_transformer - ratio = 1 (in your case, where rated = nominal voltage) - angle = 0 (in your case, without phase shifting)
Maybe one of your problems is using uk instead of ux (uk^2 = ux^2 + ur^2)? Nice regards, Chris 2016-05-10 0:33 GMT+02:00 Shuo Chen <[email protected]>: > > Dear Ray and matpower users, > > i'm writing my thesis about a data-converter for two power system > simulation softwares: PSSE@Netomac from Siemens and matpower. Here is a > problem with transformer modeling, i've read a lot in this archive but > still can't solve it, so i decide to post my question here. > > My goal is to get the same or a simular power flow convergency using the > Newton's method after converting the net topology from one to the other. > However, I'm stucked when I try to convert a Netomac net into a matpower > case. Comparing the PF results of the 2 softwares, there is always a big > deviation (by bus voltage magnitude, bus voltage angle and branch P/Q > injection). More specifically, the bus voltages in pu of matpower are all > lower than those of Netomac, the deviation could be up to 5%, like 0.977 > instead of 0.997 in Netomac. > > I simply grab all the bus/gen/branch parameters from Netomac except for > the transformer impedance, so I guess there might be a mistake when the > transformer model is built in matpower. > The transformers have 2-windings and no tap changer > > The parameters I could get from Netomac are: > > - Rated voltage of HV side winding (Un1) > - Nominal network voltage HV side (UB1? the value is equal to Un1) > - Rated voltage of LV side winding (Un2) > - Nominal network voltage LV side (UB2? the value is equal to Un2) > - Rated apparent power (equal to baseMVA) > - ur in % (may not be zero) > - uk in % (must be larger than ur) > - P0 and I0 are not given > - vector group YY0 > in matpower a transformer is treated as a transmission line, where r(p.u.) > and x(p.u.) are needed for the power flow calculation. (b is omitted in my > case) > According to the formels: > > z_pu = uk% / 100 > x_pu = uk% *(Un/UB).^2 * (SB/Sn) / 100 > r_pu = sqrt(z_pu.^2 - x_pu.^2) (here r_pu = ur%/ 100) > > Since in my case Un/UB = 1, SB/Sn = 1, so x = uk%/100, r = ur%/100, b = 0 > I set ratio = 1 and angle = 0, status = 1, angmin/max = +-360 > other values are set to 0 > > Netomac can also export a .raw file for PSSE, the conversion above will > generate equivalent r and x values as the exported .raw file. > Theoretically, with the same net topology and P/Q accuracy, the PF > convergency of the two simulation tools should be almost the same. > > Here is one more hint, as far as I know, the transformer impedance in > matpower is modeled at "to" side, while in Netomac it's modeled at "HV" > side (which is the "from" side), so there could be a difference between the > two models but i got no clue how to unify them. > > > Has anyone ever met this kind of problem before? Or the transformer is > converted in a right way, but there could be something wrong in other parts? > I know this is a tough one, hopefully I could get some hints here. Many > thanks for all! > > Best Regards > Shuo > > > >
