Thank you!
________________________________ From: [email protected] [[email protected]] on behalf of Ray Zimmerman [[email protected]] Sent: Friday, March 09, 2012 5:17 PM To: MATPOWER discussion forum Subject: Re: Transformer Impedance The quote from the manual that mentions the case with r = x = 0 is simply to make clear the definition of the tap ratio of the ideal transformer, which is only a piece of the branch model (see Fig 3-1 in the manual). A transformer is modeled as an ideal transformer in series with a pi-model line with series impedance and shunt capacitance. In any case, zero impedance branches *will* cause numerical problems, since they result in NaNs or Infs in the Ybus matrix. -- Ray Zimmerman Senior Research Associate 419A Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On Mar 9, 2012, at 10:09 AM, Jo Hoogslag wrote: Dear all, I have question concerning the impedance of transformers. I was under the impression that transformers were ideal and had impedance = 0. In the Matpower User Manual is says that "if r = x = 0, tap = Vf/Vt" (page 79). However, when I model transformers with a tap ratio, BR_R = 0 and BR_X = 0 it doesn't converge (NaN). When I model the same transformers with BR_R = 0 and BR_X = 0.1 it works. I do not understand this, have I misunderstood the manual? Cheers, Jo
