Measurements and Analysis of Power Quality in LV/MV Distribution Networks

As a candidate country for the full EU membership, Croatia has obligation to meet all EU Directives and initiatives. One of them is sustainable energy future based on a large share of distributed generation. The growing interest for integration of both renewable and other distributed energy sources emphasize the need to carry out research about influence of their integration on distribution networks planning and operation. Distributed generation (DG) is the use of small-scale power generation technologies located close to the load being served. The portfolio of distributed generation technologies includes reciprocating engines, microturbines, combustion gas turbines (including miniturbines), fuel cells, photovoltaics, and wind turbines. These technologies provide electricity to a customer at a reduced cost and more efficiently with lower transmission and distribution network losses. Distributed generation may have positively but sometimes negatively impact on the power flow, voltage profile, voltage stability, power system protection and power quality at the connection points. The power quality is addressed among challenges to achieve requested goals. Therefore the influence of distributed generation sources – small hydro, landfill gas power plant and photovoltaic roof, already connected to the network ( LV and MV) were analysed. Results of measurements were compared with the European standard EN 50160 and new national energy laws and secondary legislation. Study case comprise of power quality measurements at three DG units connected to the grid: 1. Small hydro power plant with 40 kVA asynhronous generator connected to the 0.4 kV network. Connection is accomplished by the cable/overhead line to the 0.4 kV busbar of 10/0.4 kV transformer station. Transformer station is a part of rural radial distribution network. 2. Landfill-gas power plant situated at the main waste disposal of city of Zagreb. Two generation units, each of 1162 kVA (gas powered reciprocating engines and synhronous generators) are connected by the step-up transformer and 10 kV cable to the 10 kV busbar of 10/0.4 kV transformer station. Transformer station is a part of urban 10 kV distribution network. 3. Photovoltaic roof located in the Spansko district of city of Zagreb with installed peak power of 7140 W. PV installation is a part of household connection to the public 0.4 kV urban distribution network.