Matpower uses the one line network representation in the per unit system. One of the main ideas behind the per unit system is to get rid of all the transformers and instead represent all voltages normalized to the nominal voltage of the branch/bus in question. Variable tap transformers are special transformers that can be tapped at points off the nominal ratio. That is what the tap parameter represents; it does not represent the turns ratio of the transformer. Please refer to any textbook on power systems to see how the per unit system is employed.
carlos. On Wed, Aug 29, 2012 at 1:09 PM, Cansu Yildirim <[email protected]> wrote: > Hello, > > I'm currently trying to get familiar with matpower. I have following problem > with the 'transformer off nominal ratio'. > > I need to model a transformer. The values given are following one: > > U1: 20 kV > U2: 0.4 kV > rated power: 400 kVA > no load losses: 0.61 > no load current (%): 0.1525 > u_k: 3.85 > Cu losses: 4.6 kW > switching group: Dy5 > > I have following questions: > > 1) how do I calculate the TAP? When I look into the casefiles, I can see > that the value fpr the tap is most time between 0.8 and 1.5 > I would have calculated by dividing 20kV/0.4KV=25 which does not seem > to be the correct value for the tap. > > 2) How do I identify the BR_X and BR_B ? When I look into the equivalent > circuit diagram I know that there are more components that need to be > calculated. So what > do these parameters mean for the transformer? > > I would be grateful for any help. > > > Kind regards, > > > Cansu Yildirim > >
