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A review of offshore wind power grid connection options in the Bothnian Bay

A review of offshore wind power grid connection options in the Bothnian Bay. Offshore grids for wind power integration Sisu Niskanen VTT Technical Research Centre of Finland. Contents. Finnish power system Overview of offshore wind power in Finland

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A review of offshore wind power grid connection options in the Bothnian Bay

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  1. A review of offshore wind power grid connection options in the Bothnian Bay Offshore grids for wind power integrationSisu NiskanenVTT Technical Research Centre of Finland

  2. Contents Finnish power system Overview of offshore wind power in Finland Foreseen power system development in Bothnian Bay (Bothnian Bay = Gulf of Bothnia North) A case study of grid connection in Finland for 4 OWFs.

  3. Finnish power system • Peak load 2010/01 14320 MWh/h • Annual consumption 82 TWh 2009 (88 TWh 2008) • Nordic synchronous power system; Finland, Sweden, Norway, East-Denmark • Internal North-South capacity -1400…2000 MW • AC connections in North of Finland to • Sweden 400 kV: -1500…1100 MW • Norway 110 kV: ~200 MW • DC connections in South of Finland to • Sweden: -550…550 MW, (year 2011: -1300…1300 MW, Fenno-Skan 2) • Russia (IPS/UPS-system): -1300…0 MW • Estonia (IPS/UPS-system): -365…365 MW, (year 2013: -1015…1015 MW, Estlink 2) 200 MW 200 1100 MW 1500 2000 MW 1400

  4. Wind power in Finland Offshore wind farm project plans • Bothnian Bay sum of plans 2740…3860 MW in Finland • Not all will necessarily materialize • TSO guarantees total 2000 MW sufficiently distributed WP be able to be connected in Finnish power system over following 10 yr. • In Sweden Klocktärnan planned for 2013, 660 MW. Onshore wind farm project plan of > 2 GW near the Klocktärnan.

  5. Foreseen power system development in the northern end of Bothnian Bay • Eight large projects close to each other • Total capacity 2400 – 3300 MW • Planned schedules for construction ~2013-16 • All projects will not be constructed, some will be delayed • Candidate site for a new nuclear power plant in the same area • 1500 – 2500 MW • Possibly by 2020 • According to Finnish TSO there is a need to reinforce northern interconnection between Finland and Sweden in next 10 years

  6. Case study:OWFs connection options • Four offshore sites included • Maakrunni 400 MW • Pitkämatala 600 MW • Suurhiekka 400 MW • Oulu-Haukipudas 600 MW • Radial line connection alternatives: • the nearest 400 kV overhead line and a new substation • existing 400 kV substation. One of the candicate sites for new nuclear power plant

  7. High voltage transmission lines Switching substation: PCC (Point of common coupling) Radial transmission line Substation 400/150 kV: reactive compensators Underground and submarine cables Offshore substation 150/33 kV Collecting grid: submarine cables Wind turbine: transformer, converter and generator Case study:Grid topology

  8. Case study: Investment costs of grid connection • 400 MW OWF • Transmission distance from OWF to shore is 30 km and distance from shore to PCC is 25 km. • A substation is located to 5 km from shore to inland. • The substation is connected to the PCC by 20 km 400 kV overhead line.

  9. Case study: Simulation (PSS/E) • In Bothnian Bay max. connection power at 400 kV PCC is ~1000 MW. • Larger complex should be divided into different connection points. • 2 OWF in Bothnia Bay can be connected to the same point. • Basic model for one OWF • Total capacity 400 MW, 80 turbines, 5 MW/turbine • Collection grid 33 kV • Transmission cable 150 kV • PCC 400 kV

  10. Case study:Summary • In Bothnian Bay HVAC is the most economic option in OWF grid connection. • HVDC grid connection is still too expensive if overhead lines can be used in onshore. • In Finland OWF has to operate at power factor 0,95ind…0,95kap • Reactive power compensators at PCC and/or substations: • submarine cables produce capacitive current • OWF capacity factor is about 0.40 and transmission lines are usually operated at capacitive power factor. • The transmission distance from offshore to onshore substation and PCC.

  11. Technology • Conventional high voltage AC system • Grid voltage in Finland: 110, 220, 400 kV • <250 MW OWF can be connected to 110 kV transmission system with some limitations. >250 MW OWF have to connect to 400 kV transmission system. • HVDC system • ABB HVDC light and Siemens HVDC plus • ±150 kV, max ~570 MW • ±320 kV, max ~1200 MW • LCC (Line commutated converter) • Higher voltage and transmission capacity • Need reactive power compensators and stronger AC network than Light or Plus technology

  12. HVDC grid options Options of small scale HVDC super grid Connection between OWFs Parallel connection with internal North-South transmission grid Cross-border connection between Finland and Sweden

  13. Future work • Analysis on the effect of different offshore grid options in Bothnian bay on grid • Cost-benefit analysis of connection using unit commitment and dispatch models • Assess the need for additional connections and their capacity across Bothnian bay • cross border transmission capacities • bottle neck operation • general power transfers

  14. Acknowledgements • This study has been co-steered by TEKES, Fortum Oyj, wpd Finland Oy, Pohjolan Voima Oy, Fingrid Oyj

  15. VTT creates business from technology

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