Hi Oliver,
did you consider that the chosen base voltage has to be transformed
depending in which voltage level you are calculating?
If you choose e.g. baseMVA = 1MVA and baseV = 20 kV, but your cable is
on the 10 kV side of the transformer, you have to calculate the
impedance of the transformer, rated to the 10 kV side and the cable
impedance with a base voltage of 10 kV. EXCEPTION: If the transformer
has a "Übersetzungsverhältnis" different from 1/2 (in this case) you
have to consider this also. If your chosen Voltage is 20 kV und the
ratio is 1/3, then the rated voltage would be 20/3 kV.
Sincerely/Grüße
Simon
Am 10.11.2011 11:05, schrieb [email protected]:
Dear Sir or Madame,
I'm a student at the Otto-von-Guericke University in Magdeburg, Germany and I'm
about to get started in using Matpower for some network analysis problems in
Low Voltage networks (230V rms). I try to calculate how the voltages at the
busses/nodes change by adding more decentral energy sources like photovoltaics.
I tried to use Matpower and have got some problems. It would be very nice if
you could give me some advice in solving my modelling problem. I'd be very
happy about any help.
At first view Matpower seems to be usefull for solving these problems. At first
step I tried to build a network of only to busses (#01 to represent a energy
source (transformator from medium voltage to low voltage, modelled as a
generator) (#02: 100kW Load) in order to get to know Matpower itself. But I
found a problem, which I can't solve right now:
I have to set a baseMVA-Value and a base voltage. So I decided for some values.
The lower the chosen MVA-Value the bigger the chance that the iteration won't
converge. But in Low-Voltage I can't use some GVA or TVA-Values just in order
to get it work, can't I?!
For the Impedance of the branch, connecting both busses, I calculated values
for a 300m piece of cable. Than I devided the Impedance-values by the
baseImpedance in order to get p.u. Impedances as claimed by Matpower. The
baseimpdance was calculated by Basevoltage * Basevoltage / Base power
(MVA-Value) as written in my collection of formulas.
But the impedances of the branch were so small that there's almost no powerloss and
no decrease in the voltage between bus 1& 2.
I tried to scale up my Lowvoltage problem by setting 100MW for (real) 100kW and
230kV for 230V(real). But it didn't work. The modell didn't converge or gave
wrong values back. So I want to know whats the best way to modell my
Low-Voltage-problem in Matpower?
In order to give you an idea, what I tried, here are some very short .m-files, which show
my Problem at the decripted example. The file startbaresSkript is a runable file, which
calculates the impedances and than passes them into the modell. The modell itself is just
set up with some 'random' values just to create the structure and fill in correct values
afterwards by using the "startbareSkript".
Nomenclature: In Germany "U" is used for Voltage and the "_bez" in variable
names express that Base-Values for p.u. - calculations are ment.
I also tried for the Calculation of the base impedance to scale down the
MVA-Base and the Base-Voltagein (kV) down to SI-measurement units, but it
did'nt work either.
Somehow I did'nt found a good way to cope with low voltage networks decripted
in the manual.
Can you help me?! Which settings have to be done to calculate a
low-voltage-network with matpower?
The concrete Data are:
230 V (RMS) between phase and neutral Line, 3 phase-model (Star-circuit,
symmetric Loads and generations!)
Loadvalues somewhere between 2-100 kW at each bus (fix Load/ fix generation)
and a balancing generator representing the connected network to upper
Voltage-Network-Layers...
I would be really happy, if you could give me some hints, ideas or tipps to
cope with that problem.
Thanks a lot!
Yours sincerely,
Oliver Kopp
Germany
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