Study <strong>for</strong> Optimization <strong>of</strong> Connection Point <strong>of</strong> new <strong>400</strong> kV Interconnection to Serbia1. BASIC INFO FOR THE PROJECT AND THE STUDYTransmission system operators <strong>of</strong> Macedonia (MEPSO) and Serbia (EMS) have initiated <strong>project</strong><strong>for</strong> construction <strong>of</strong> <strong>400</strong> kV <strong>interconnection</strong> line <strong>between</strong> their <strong>power</strong> <strong>systems</strong>. Two feasibility studies arecompleted so far, investigating basic technical characteristics and viability <strong>of</strong> the <strong>project</strong>:– Technical and Economical Aspects <strong>for</strong> Interconnection <strong>of</strong> Power Systems<strong>of</strong> Serbia and Macedonia with <strong>400</strong> kV OHL Nis – Leskovac – (Vranje) – Skopje,EKC & EPS – Belgrade, ESM – Skopje;– Study <strong>for</strong> new <strong>400</strong> kV <strong>interconnection</strong> lines <strong>between</strong> Macedonia – Serbiaand Albania – Montenegro,TEN – <strong>project</strong>, HTSO – Athens, ESM – Skopje, EKC & EPS – Belgrade, EPCG – Podgorica,KESH – Tirana.At present there are three <strong>interconnection</strong> lines <strong>between</strong> electric <strong>power</strong> system <strong>of</strong> Macedonia andneighbouring system on the north: one OHL on <strong>400</strong> kV voltage level and two 220 kV OHL-s that connectregions <strong>of</strong> Skopje and Kosovo. Skopje is region in the country with the largest demand. Electricity supply <strong>of</strong>Skopje region is mainly covered from TPP Bitola production and imports through north interface anddistributed by two <strong>400</strong> kV nodes: SS Skopje 5 and SS Skopje 4. In a last few years, unavailability <strong>of</strong> 220 kV<strong>interconnection</strong>s that are out <strong>of</strong> operation since 1999 has deteriorated reliability <strong>of</strong> <strong>power</strong> <strong>systems</strong> in theregion.Unavailability <strong>of</strong> 220 kV OHL-s to Kosovo affects electricity exchange in north – south direction,mostly in summer months while Greece has peak demand and big imports from other <strong>power</strong> <strong>systems</strong>.Transmission capacity <strong>of</strong> the whole <strong>interconnection</strong> north – south is decreased: Nis – Kosovo – Skopje –Dubrovo – Thessaloniki. Outage <strong>of</strong> <strong>400</strong> kV busbars in SS Kosovo is especially dangerous regime. Electricityflowing to south overload the rest <strong>of</strong> <strong>interconnection</strong> links (220 kV OHL Prizren – Fierza, 220 kV OHLPodgorica – Vau Dejes and <strong>400</strong> kV OHL Blagoevgrad – Thessaloniki) that can lead to cascade outages and<strong>power</strong> supply interruptions <strong>of</strong> particular regions. In fact, similar events have been reason <strong>for</strong> blackout <strong>of</strong><strong>systems</strong> in Macedonia, part <strong>of</strong> Greece, Serbia and Montenegro on 25 th August 2007. Situation is critical inthe period <strong>of</strong> overhauls <strong>of</strong> other capital electricity facilities as well. Constantly increasing bulk <strong>power</strong>exchange <strong>between</strong>/through EPS-s <strong>of</strong> Macedonia and Serbia impose construction <strong>of</strong> new <strong>interconnection</strong> linenecessary.New link toward north will significantly improve quality, flexibility and reliability <strong>of</strong> <strong>power</strong> supply<strong>of</strong> Skopje. Construction <strong>of</strong> this <strong>400</strong> kV line is important <strong>for</strong> both <strong>systems</strong>. It will improve security, reliabilityand operability <strong>of</strong> the wider region and create conditions <strong>for</strong> larger amount <strong>of</strong> electricity exchange.Realization <strong>of</strong> <strong>400</strong> kV OHL to Nis (SER), together with recently established <strong>400</strong> kV OHL Bitola(MKD) – Florina (GRE) and ongoing construction <strong>of</strong> <strong>400</strong> kV OHL Stip (MKD) – Chervena Mogila (BUL)will strengthen electricity corridor north – south, multiplying transmission capacities.According to preliminary plans <strong>for</strong> new <strong>400</strong> kV <strong>interconnection</strong>, it will be designed as single circuit<strong>400</strong> kV line with lattice type steel towers with bundle <strong>of</strong> two conductors per phase, type Al/Fe 490/65mm 2 /mm 2 . On the Serbian territory, OHL starts at <strong>400</strong>/220 kV SS Nis. In order to improve <strong>power</strong> supply insouthern part <strong>of</strong> Serbia, two new <strong>400</strong> kV substation will be build and connected on this line: SS Vranje andSS Leskovac. Length <strong>of</strong> the line from SS Nis to Macedonian – Serbian border is about 150 km.Connection point on Macedonian side is still not defined. Interconnection may be connected eitherin one <strong>of</strong> existing <strong>400</strong>/110 kV substations in Skopje, SS Skopje 5 or SS Skopje 4, or in planned <strong>400</strong>/110 kVSS Stip. Having intention to make right choice <strong>of</strong> connection point on Macedonian territory <strong>of</strong> new<strong>interconnection</strong>, MEPSO carried out techno-economical analyses that identify the best solution.4
Study <strong>for</strong> Optimization <strong>of</strong> Connection Point <strong>of</strong> new <strong>400</strong> kV Interconnection to Serbia2. VARIANTS FOR CONNECTION POINTMEPSO experts considered a lot <strong>of</strong> variants <strong>for</strong> connection point during preparation phase <strong>of</strong> the<strong>project</strong> <strong>for</strong> new <strong>interconnection</strong>. On the beginning, variants have been analyzed from the viewpoint <strong>of</strong>availability <strong>of</strong> spatial corridors <strong>for</strong> OHL-s, possibilities <strong>for</strong> accessing and upgrading candidate substations aswell as possibilities <strong>for</strong> practical accomplishment <strong>of</strong> variants and economical characteristics <strong>of</strong> investment.Figure 1. Corridors (in dark blue) <strong>for</strong> new <strong>interconnection</strong>s to northern EPS-sIn the meantime, creation <strong>of</strong> second <strong>interconnection</strong> link <strong>between</strong> system <strong>of</strong> Kosovo andMacedonia has been initiated. For this purpose is <strong>for</strong>eseen to use at least one <strong>of</strong> existing 220 kV OHL-sSkopje 1 – Kosovo A, by refurbishment <strong>of</strong> one <strong>of</strong> the lines or by using the corridor <strong>for</strong> construction <strong>of</strong> newline on <strong>400</strong> kV voltage level. Existing 220 kV lines Skopje 1 – Kosovo A are out <strong>of</strong> operation <strong>for</strong> a long timeand are highly deteriorated on the territory <strong>of</strong> Kosovo. Decision on voltage level <strong>of</strong> second <strong>interconnection</strong> toKosovo is interdependent on future <strong>of</strong> 220 kV voltage level in Macedonia. Development plans <strong>of</strong>Macedonian EPS do not consider expansion <strong>of</strong> 220 kV level, but plan is to discard this voltage level. Thatmeans that second link to Kosovo should be implemented on <strong>400</strong> kV voltage level with adequate choice <strong>of</strong>connection point in Macedonian network. Variants in the Study consider these possibilities as well, makingan ef<strong>for</strong>t <strong>for</strong> simultaneous optimization <strong>of</strong> two new links towards north: second line to Kosovo and new <strong>400</strong>kV line to Nis (i.e. to Vranje – Leskovac – Nis).Based on a<strong>for</strong>ementioned findings and conclusions, few variants are defined and technoeconomicalanalyzes are per<strong>for</strong>med.5
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