Dear Chris,
thanks for your advice! I did some experiments and found out that by
small power systems there shold be no difference between Netomac and
matpower, while by larger ones it's not that simple.
Probably it's not a matter of transformer model, other factor might
also make a difference, I need more experiments to prove this.
Best regards
Shuo
Zitat von Chris Prokop <[email protected]>：
Dear Shuo,
I'd try to simulate a simply network with 1 reference bus with 1
transformer and 1 subsequent load to test the behaviour between Matpower
and netomac.
I'm not used to netomac, so can't help here directly.
Nice regards,
Chris
2016-05-10 13:22 GMT+02:00 Shuo Chen <[email protected]>:
Dear Chris,
thanks for your reply, actually we are getting the same transformer data.
In my power system uk is far more larger than ur (more than 50:1), so it
can be assumed that ux = uk.
i'm wondering whether there is any little difference between netomac and
matpower by modeling the transformer, so that even if I give them the same
input, PF results could still differ.
best regards
Shuo
Zitat von Chris Prokop <[email protected]>：
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
