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Low voltage (LV) grids are characterized for being unbalanced due to: 1) the considerable amount of single loads, 2) unbalanced three-phase loads, and 3) unequal impedances in the cables/lines that are used in these grids. Given that, and despite the effort to reduce unbalances (for instance by distributing single phase loads equally on the three phase system), if no other action is performed, unbalanced three-phase currents would be translated to MV lines, and then to HV lines (correct me if I am wrong here). So I wonder where the unbalance is handled in case of a LV grid encounter huge degree of unbalances. Is it in the LV/MV or MV/HV substations? if so, what kind of devices or techniques are used for that purpose?

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Bur Nor
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  • For consumers, usually you have so many loads at the ends that the load is rather evenly distributed, statistically. Even if everyone in my street would switch on only those loads on one phase, for the whole district the difference is negligible. Industrial consumers need to make sure themselves that they load the net rather equally. The most common way to equalize for big differences in LV nets is a probably zigzag transformer. – PlasmaHH Nov 15 '17 at 12:11
  • Hi @PlasmaHH, I am not sure if unbalances become neglectable when aggregating single loads, cuz there are plenty of old articles (from 90`s) in the literature that address unbalanced in distribution grids. – Bur Nor Nov 15 '17 at 14:14
  • It depends on what level you are looking at. For resident areas, people don't mind if the voltage is not very evenly distributed among the phases, as such on that level corrections are not necessary. If you go to the transmission line levels and back to the generator, things get more complicated as in the end, in the generator it matters. For there you have many ways to compensate, in the end mostly boiling down to a way to route power from one phase to another. – PlasmaHH Nov 15 '17 at 14:19
  • yes, my point was that if some mitigation were done before the unbalanced currents produced at LV level scaled to MV or even HV (through transformers) cuz as you said having unbalances at HV are not desire giving that it might cause the trip of generation units. – Bur Nor Nov 15 '17 at 15:41
  • all mitigation I know of is done at the HV level, LV would be far too many places for not much gain (since you would need to do it at HV level anyways) – PlasmaHH Nov 15 '17 at 15:45

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