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Study for Optimization of Connection Point of new 400 kV Interconnection to Serbiapower market leads to lower power price in the countries that imports. Also, countries that exports electricityprofit from opening the market because can offer their products for a bigger price.Different countries in the region have peak load in different periods of the year. Because the newinterconnection transmission capacities are enlarged it allows to use bigger part of the other countries’reserve in order to cover regimes with peak load. It reduces the investment in installed production capacity ofnational power reserve.Increased transmission capacity and market development are condition for promoting the regionaldispatch which brings lower production costs on global level because of accessibility of units with a differenttype of prime movers and low price for production.Other effects come from telecommunication services which are achieving by installing opticalgrounding wires in new interconnections. This feature eliminates EMS’s and MEPSO’s costs for rentingtelecommunication channels and at the same time there is possibility to offer telecommunication service tothird parties.New interconnection reduces the need for exchange of reactive power in the region. Aftercommissioning the interconnection, it will generate above 100 MVAr which will be injected in the network.It is very difficult to quantify economically the needs of reactive power in the region.New interconnection is very important in increasing the security of supply in the Macedonian andGreek power systems, because it reduces the risk of appearance of unreliable regimes and partial blackouts inthe southern systems which have already happened few times in the past.4. CONCLUSIONTechno-economical analyzes has launched variant 2 as the most adequate solution for connectionpoint of new 400 kV interconnections to north. Following topology is recommended in variant 2:– For second 400 kV line to Kosovo to use corridor of one of existing 220 kV OHL-s Skopje 1 –Kosovo A and to connect line in SS Skopje 5.– New 400 kV interconnection to Serbia to be connected at new 400/110 kV SS Stip.Variant 1 is also economically competitive, which proposes both new interconnections to beconnected at SS Skopje 5. Even though this variant fulfils all predefined technical criteria, somedisadvantages from technical viewpoint can be detected.Specifically, in SS Skopje 5 are foreseen three interconnection lines. In case of outage of 400 kVbusbars in SS Skopje 5, all three interconnections will be disconnected and regional transits can be seriouslyjeopardized. Busbars contingency are not standard criterion in procedure for network planning and selectionbetween different network expansion plans, but in this case it is recommended to impose this criterion assupplementary condition for variants evaluation. In addition, 110 kV busbars at SS Skopje 1 * have largestshort-circuit current in Macedonian network. For this node can be expected problems in the futureconcerning characteristics of existing high-voltage equipment that can be endangered with too high shortcircuitstress. In variant 1 short circuit can be driven up to 40 kA. Main reason for these values of shortcircuits is large concentration of lines and power plants at/near this node.Therefore, it is recommended variant 1 to be skipped as possible solution and to proceed furtherwith variant 2.* In fact, Skopje 5 and Skopje 1 is the same substation, where Skopje 1 refers to 110 kV busbars andswitchyards and Skopje 5 refers to 400 kV busbars and switchyards. Skopje 5 and Skopje 1 are connected with two400/110 kV autotransformers, with 300 MVA each unit.14
Study for Optimization of Connection Point of new 400 kV Interconnection to SerbiaFigure 10. Optimal solution for connection point of new interconnections to northern EPS-sKosovo BNisSofiaSEZAPHPP VrutokHPP B. MostSkopje 5Skopje 4KumanovoC. MogilaHPP SpiljeHPP GlobocicaStipDubrovoBlagoevgradOhridBitolaMariovoFlorinaThessalonikiFigure 11. Vision for network development in Macedonia on long-term horizon15
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