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
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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.
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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)
1100 MW 1500
200
MW
200
200
0 M
W 1
400
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Wind power in FinlandOffshore 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.
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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
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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
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Case study:Grid topology
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
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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.
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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
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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.
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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
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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
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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
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Acknowledgements
This study has been co-steered by TEKES, Fortum Oyj, wpd Finland Oy, Pohjolan Voima Oy, Fingrid Oyj
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