I have one remaining question, if you please. How do I define the r,x, and b
value for a branch in which you have a transformer? I can imagine that for the
x value one would use the formula x= u_k x (U^2/S) , for the b value
Y=1/Z=1/(r+jx)=g+jb and then take the b value.
But how do i identify r? I just know the formulas for a transformer to identify
the copper and iron losses. But what about BR_X in this case? Regards, Cansu
> Subject: Re: Help with modelling a transformer & TAP
> From: [email protected]
> Date: Wed, 29 Aug 2012 20:39:34 +0200
> To: [email protected]
>
> Alright, thanks a lot once again! Now I should be able to model tap
> transformers as well!
>
> Regards,
>
> Cansu
>
>
>
> On 29.08.2012, at 20:30, "Carlos Murillo" <[email protected]> wrote:
>
> > Yes, although the default value of 0 (meaning no tap switching capability)
> > actually means a 1.0 tap, that is, a nominal ratio.
> >
> > carlos.
> >
> > On Wed, Aug 29, 2012 at 2:26 PM, Cansu Yildirim <[email protected]>
> > wrote:
> >> Thank you very much for your quick answer Carlos!
> >>
> >> So in my case, since I have just a normal transformer, this would mean
> >> that the tap parameter is zero right?
> >>
> >> Regards,
> >>
> >> Cansu
> >>
> >>
> >>
> >> On 29.08.2012, at 19:57, "Carlos Murillo" <[email protected]>
> >> wrote:
> >>
> >>> 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
> >>>>
> >>>>
> >>>
> >>
> >>
> >
>
>
