I also suspect it is a reactive power or voltage problem. Is there a voltage limit binding at the buses where energy is not supplied (I assume you are using dispatchable loads)? If so, you might get some insight from doing some perturbation analysis. Simply change that voltage limit by a very small amount and see how the dispatch changes. My guess is that the only way to maintain the voltage is by using the expensive distributed generators. Shifting generation to the grid infeed would likely result in more load shedding to keep voltages in line. Presumably load shedding is even more costly than the distributed generation?
-- Ray Zimmerman Senior Research Associate B30 Warren Hall, Cornell University, Ithaca, NY 14853 phone: (607) 255-9645 On Feb 11, 2014, at 5:48 AM, angelina sirri <[email protected]> wrote: > Dear Dr Zimmerman, > I am using an 11kV distribution system, which is consisted of two radial > circuits connected by a normally open point. The network has one grid infeed > (Vg=1) whereas all the other nodes where occupied only by loads (with Vm<1). > Now I increase the loading of the circuits and have added distributed > generators in all the load buses, which will only operate in case there is a > line fault in the system(otherwise there is no need for them to operate > because the grid infeed can give really high power, comparing to the load and > the lines rating is also really big) . For the voltage problems, I have > added reactive power in each node. > The thing that confuses me is , that when there is a line fault (the worst > case scenario line loss), there is always energy not supplied , although a > path from the main supply exists and also the rating of the lines allows > that power to pass through the line. This happens mainly for the most distant > nodes. In that case, all the available distributed generators generate at > their Pmax , but the grid infeed value is really small. > Why the opf prefers to use the really expensive generators of the distant > nodes (used for the energy not supplied) instead of absorbing that power from > the free of cost grid infeed? I can guess that is a reactive problem or a > voltage problem but I cannot find a suitable solution. > Any help would be of high importance, > King Regards, > Angelina
