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In the paper design improvements of distribution transformers related to improved energy efficiency and environmental awareness are discussed. Eco design of transformers, amorphous transformers, voltage regulated transformers and transformers filled with ester liquids are analyzed. As a consequence of growing energy efficiency importance, European Commission has adopted new regulation which defines maximum permissible levels of load and no-load losses of transformers with rated power ≤ 3150 kVA, and minimum peak efficiency index for transformers with rated power > 3150 kVA up to 40 MVA. The impact of new regulation on the design and economy of transformer is presented. Amorphous transformers, with up to 70 % lower no-load losses in comparison to the conventional transformers, could be an alternative with respect to energy efficiency. Although their initial price is higher than the price of conventional transformers, some studies show that they might have economic advantages. The increasing penetration of distributed energy sources can cause an increase in voltage variations in low voltage networks. To keep the voltage within limits defined by EN50160, voltage regulated distribution transformers could be used. Although mineral oil has been used as a dielectric fluid in transformers for many years, there are some environmentally friendlier alternatives – natural and synthetic ester-based fluids.

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The ultimate goal in today’s electricity business in Europe is market integration on pan-European level that will introduce transparency and competition between market players, incentives to clean energy development, as well as high quality of supply to the end-customers. To achieve these goals, in South-East Europe (SEE) there are number of barriers and uncertainties, one of which is linked with the possible new undersea HVDC connections between SEE and Italy. With the support of the United States Agency for International Development (USAID) and coordination of the United States Energy Association (USEA), within the framework of the Southeast Europe Transmission System Planning Project (SECI), a detailed analysis has been accomplished on the impact of one or more undersea HVDC cables between Italy and SEE on power system operation and electricity market development [1]. Special emphasis to this analysis is given by the fact that SECI has been one of the longest running projects in the region. It started in 2001 with active participation of all regional TSOs, including continuous updating of power system and electricity market models and its harmonization of constant changes in power system planning. It is of utmost importance in the environment of constant changes of national power system development plans and needed further steps for full market opening and integration in the region. SEE power systems and market1 were modelled using the most relevant power system and market simulation and optimization softwares. Both system and market comprehensive models have been verified by all SEE TSOs. Study analyses were divided in two parts: 1) market analysis and 2) network analysis. The market study investigated expected generation pattern, power exchanges and wholesale prices in SEE, taking into account regional market synergy, the new links with Italy, and high level of RES integration. Bulgaria and Romania are currently the main exporters in SEE. Significant power exchanges in the North-South/Southeast direction are related to the fact that the GR, MK, ME, HR and AL are mainly importing, plus the influence of Italy importing over new potential HVDC cable(s). Network analysis dealt with power flows, network bottlenecks and voltage profiles in given market scenarios. Finally, the results of this comprehensive market simulation comprised of the following: Countries electricity balance (production, consumption and exchanges) Electricity prices for each country Cross-border power exchanges (MWh/h) for each border in the region on hourly basis HVDC link loadings (MWh/h) for each HVDC submarine cable on hourly basis Location and frequency of market congestions in SEE (NTCs full between areas with price difference) All those analyses have been performed in two different transmission network development scenarios: Base case scenario: with planned HVDC ME-IT Alternative scenario: with planned HVDC ME-IT, and HVDC HR-IT, and HVDC AL-IT In this way one of the most important uncertainties (new HVDC links SEE – Italy) for future power system and market operation in SEE, have been evaluated both in technical and market sense, using the most relevant inputs and model.

The southern wing of the Croatian transmission network was constructed for 220 kV in the early 1960’s, with additional 400 kV reinforcement at the end of 1970’s. Its route of more than 200 km is quite demanding due to extreme climate, environmental specifics and related costs. However, operational experience during more than 50 years has been quite positive. Nowadays, at the end of its lifetime it is again extremely important to analyze and select the best option for network revitalization and development to serve the network users for the next 50 years, but in very different conditions of technological development, more restrictive environmental requirements, electricity market conditions and large scale RES integration. Moreover, special attention should be given to the potential opportunity and need to use this revitalization also for new interconnection to the power system of Bosnia and Herzegovina (BiH). Five main options have been initially selected as topology candidates for problem resolving. Detailed methodology and criteria for the selection of optimal option (revitalization and development scenario and topology) were developed and approved by all involved stakeholders. For selected option, based on comprehensive analyses and approved methodology , for further detailed analyses ( system reliability, technical design, investment, economics /CBA/ and environmental analyses) have been prepared, including assessment of its impact on transmission tariffs of each country. Sensitivity analyses to the most uncertain variables (investment costs and CO2 prices) were also performed. The environmental and social assessment was very demanding due to the complex governance structure and three legal frameworks to be respected (two countries, along with two entities in BiH). The Project impact was evaluated with respect to: air quality, water quality, waste management, noise, biological diversity, electromagnetic field, social measures and protected areas. This paper presents above mentioned analyses, findings and recommendations, as the most comprehensive analytical approach to the transmission line development that’s ever been applied in this region.