Ray, Thank you very much for your reply. To go through your points step-by-step:
1. Yes, I am sure that my p.u. parameters are correct. I calculate them with the same methodology as for smaller European countries – and there, the values match the expectations nicely. So I think this is not the problem here. 2. The voltage limits I am imposing are even less restrictive than the real voltage limits. So I have already relaxed that constraint, yet I can not achieve convergence. 3. The shunt capacitors are the critical point in my view. I am not using any in the current network, since I have no information about placement and dimensioning of the capacitors in the real system. So effectively, I am not doing any voltage support, which should explain the voltage drops. But my main problem with this issue is the following: If I understand correctly, the inserted shunt conductance and susceptance are imposed on the system. Meaning the MW and MVAr demanded/injected by the shunt capacitor are not being optimised during the OPF run. Is that correct? If my understanding about the shunt conductors is correct, how can I know beforehand, how much voltage support I will need at a certain substation? Would it make sense to do an iteration where I re-run the runopf() several times while adjusting the shunt values as a function of the voltages after each run of runopf()? Or do you recommend an alternative strategy here? I greatly appreciate your inputs. Any hints would help me. Best Regards, Patrick Eser From: Ray Zimmerman <[email protected]<mailto:[email protected]>> Reply-To: MATPOWER discussion forum <[email protected]<mailto:[email protected]>> Date: Monday 30 March 2015 15:21 To: MATPOWER discussion forum <[email protected]<mailto:[email protected]>> Subject: Re: Voltage drops of very long transmission lines Here are few questions that might be helpful in steering you toward a solution ... - If you are convinced that you have the correct p.u. parameters for the transmission lines? Errors in the p.u. conversion could result in such problems? - If you are attempting to model an existing system, currently in operation, are you sure you are using voltage limits that include the actual normal operating point? - Are you missing any shunt capacitors used for voltage support? - Have you tried a simple power flow to see how far out of range the voltages are? - Have you tried using a continuation power flow to see if your operating point is beyond the point of voltage collapse? - Have you looked at FAQ #5<http://www.pserc.cornell.edu/matpower/#pfconvergence>? Best, Ray On Mar 30, 2015, at 5:12 AM, Eser Patrick <[email protected]<mailto:[email protected]>> wrote: Dear MATPOWER community, I am currently building a transmission system database for an emerging nation. When running an OPF simulation for this system, I encounter the problem of massive voltage drops over particularly long lines. This is hardly surprising, since some lines of the system are longer than 400 km. Combined with realistic reactances per km, this yields high per unit X (and B) values, and hence voltage drops. When I artificially reduce the reactance and susceptance values, I am able to achieve convergence. My questions are: Is there a way of solving this issue, without tampering with the X and B values? I have played around with the tap ratios, but unfortunately, these are not within the parameters of the optimisation (i.e. they are fixed a priori). I have also tried adding a fictitious “reactive power generator” at each substation, without success. Any help would be appreciated. Thanks! Best Regards, Patrick Eser
