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Thursday, 13 March 2014
09:00 - 10:30 Electrical aspects and grid integration
Science & Research  


Room: Llevant
Session description

The grid integration of wind power has always been a challenge. In this session a range of speakers from academia and industry will address the impact of wind on network operation and the development of a large scale offshore HVDC grid, offshore systems, the state-of-the-art in HVDC technologies, as well as more specific topics including the design of offshore networks from a reliability perspective and the transient response of HVDC links.

Learning objectives

  • Understand the effect of wind power on grid operation and development via case studies
  • Get an overview of the state of the art in HVDC offshore grid research
  • Get acquainted with specific topics of offshore grids, including reliability and transient response aspects
Lead Session Chair:
Stavros Papathanassiou, National Technical University of Athens, Greece

Co-chair(s):
John Olav Tande, SINTEF, Norway
Vladislav Akhmatov Energinet.dk Transmission System Operator of Denmark, Denmark
Co-authors:
Vladislav Akhmatov (1) F P Jan Havsager (1) René Thorsen Starup (1) Hans Abildgaard (1) Peter Borre Eriksen (1)
(1) Energinet.dk Transmission System Operator of Denmark, Fredericia, Denmark

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Presenter's biography

Biographies are supplied directly by presenters at EWEA 2014 and are published here unedited

Vladislav Akhmatov received the M.Sc. (1999) and Ph.D. (2003) degrees in electrical power systems from the Technical University of Denmark. He worked with NESA, now part of DONG Energy, in Copenhagen, Siemens Wind Power in Brande first as an engineer and later as a Chief Specialist and with the Technical University of Denmark as a Professor with special responsibilities in electric power systems. He returned to Energinet.dk in 2010, the Danish transmission system operator, as a Senior Engineer, Emeritus Professor. His main interests include power systems and wind power assessment.

Abstract

Plans for significant amount of wind power and voltage stability of the Danish island of Bornholm

Introduction

This presentation includes the grid-connection and dynamic voltage stability studies of Energinet.dk
on establishment of additional wind power, by rates of 50MW, 100MW, 150MW and 200MW, connected
to the Bornholm 60 kV grid, with the maximum peak consumption of about 58MW, by the year 2020.
The grid connection topologies are also investigated and discussed. The study has concluded that
grid-connection of between 50MW and 100MW wind power would not worsen dynamic voltage stability
of Bornholm, i.e. keeping at the present level. Connection of more wind power requires detailed grid-expansion
and socio-economic studies.

Approach

At present, the wind turbines stay for about 30% of the electric energy consumption of Bornholm.
Commissioning of only additional 20MW wind power would imply that about 50% of electric energy
consumption is covered by wind power [1]. This is the Danish governmental target for 2020.
Establishment of additional, up to 200 MW, wind power by the year 2020 has been proposed.
The wind power shall be within areas appointed by the Danish Energy Authority (Energistyrelsen)
just few km off the Bornholm coast [2]. Energinet.dk has conducted preliminary grid-integration studies
using the 60 kV distributuion system model and the models of existing wind turbines, PV, thermal power units,
consumption, and connection to the South Swedish transmission system by a submarine cable,
by scenarios with establishment of additional 50MW, 100MW, 150MW and 200MW wind power in Bornholm.
The dynamic voltage stability investigations have included the Bornholm system response to three-phase
short-circuits in all 60 kV substations, some 60 kV lines with permanent tripping and sub-sequent outage
of power generation units. The wind turbines are modelled by conventional technology and by
converter-grid-interfaced wind turbines. The analysis included interpretation of the dynamic voltage profiles,
loadings of the lines and the cable connection to Sweden as well as definition of the dynamic stability range
of the island. The preliminary grid studies should answer the two main questions. The first questions has
been how much wind power, by steps of 50MW, would be connected to the Bornholm 60 kV grid without
the grid expansion and commissioning of the second cable to Sweden. The second question has been
whether such a significant amount of additional wind power will worsen dynamic voltage stability of Bornholm.

Main body of abstract

The Danish island of Bornholm is situated just south of Sweden. The electric power system of Bornholm
comprises a meshed (distribution) 60 kV grid and radial 10 kV and 0.4 kV grids. Through a 60 kV 0.66 kA
submarine cable and a 135/60 kV 63 MVA transformer the Bornholm power system is connected to the
Swedish 135 kV transmission system. The distribution system operator (DSO) Oestkraft-Net owns and operates
the power system of the island and the Danish transmission system operator Energinet.dk owns the cable to
Sweden. The electric power generation contains thermal and biogas based units, wind turbines and photo-voltaic
(PV) panels. In 2013 figures, the electric power consumption ranges between 15MW (a summer night) and
55MW (a winter day). At present, the wind turbines stay for about 30% of the electric energy consumption of
Bornholm. In relation to the area, population and electric energy consumption, the island of Bornholm comprises
1% of Denmark. The power system of Bornholm has many characteristics of the mainland Danish system.
Commissioning of additional 20 MW wind power would imply that about 50% of electric energy consumption
is covered by wind power [1]. This is the Danish governmental target for 2020. Due to resembling all main
characteristics of the mainland Danish power system and unique position with the grid-integration of renewable
energy sources, Bornholm has become the play-ground for research and demonstration projects with advanced
energy solutions at keeping a sufficient high level of security-of-supply. Establishment of additional, up to
200MW, wind power by the year 2020 has been proposed. The wind power shall be within an area appointed
by the Danish Energy Authority (Energistyrelsen) just few km off the Bornholm coast [2]. Energinet.dk has
conducted preliminary grid-integration studies by scenarios with establishment of additional 50MW, 100MW,
150MW and 200MW wind power in Bornholm. The dynamic voltage stability studies have used the 60 kV
distribution system model of Bornholm, with representation of the 60/10 kV substations, thermal generation
units in the main city of Ronne, wind turbines, PV units, consumption and the cable connection system to
Sweden. The wind turbines are distinguished by their technology, i.e. conventional, fixed-speed turbines, and
modern, converter-grid-interfaced wind turbines. The wind turbines are modelled using validated models.
The dynamic response of the Bornholm 60 kV system is evaluated by simulations of three-phase short-circuits
in the 60/10 kV substations, 60 kV lines with post-sequent permanent tripping, and post-sequent outage of
generation units. The commercially-available simulation program DIgSILENT has been applied. The analysis
included evaluation of the voltage profiles, line loading conditions and definition of the dynamic stability range
of the distribution system of Bornholm. The preliminary grid studies should answer the two main questions.
The first questions has been how much wind power, by steps of 50MW, would be connected to the Bornholm
60 kV grid without the grid expansion and commissioning of the second cable to Sweden. The second
question has been whether such a significant amount of additional wind power will worsen dynamic
voltage stability of Bornholm. This presentation includes the preliminary grid-connection and dynamic voltage
stability studies of Energinet.dk on establishment of addition wind power connected to the Bornholm 60 kV
grid. The grid-connection topologies are also investigated and discussed. The study has concluded that
grid-connection of between 50MW and 100MW wind power would not worsen dynamic voltage stability of
Bornholm, i.e. keeping at the present level. Plans with establishment of more than the above given range of
wind power should be followed with detailed investigations on the most suitable, technical and economic
ways of the grid expansion in and power transport from the island.

Conclusion

Energinet.dk has conducted the preliminary grid-connection and dynamic voltage stability studies on
establishment of addition wind power connected to the Bornholm 60 kV distribution grid. The wind power
grid-connection scenarios are by the capacities of 50MW, 100MW, 150MW and 200MW located in areas
appointed by the Danish Energy Authority – Energistyrelsen. The grid-connection topologies of the wind
turbines to the existing 60 kV grid of Bornholm by means of submarine and land cables, transformation
stations and definition of the connection substation are also investigated and discussed. The study has
defined the dynamic stability range of the power grid of the island, which is a dynamic voltage profile which
should be maintained to conclude stable operation regimes. The study has concluded that grid-connection
of between 50MW and 100MW wind power would not worsen dynamic voltage stability of Bornholm, i.e. keeping
at the present level, without extensive grid reinforcements on the island or establishment of the second cable
connection to Sweden. Scenarios with establishment of more than the above given range of wind power should
be followed with detailed, in-depth investigations on the most suitable, technical and eco-nomic ways of the grid
expansion on and power transport from the island. Design, implementation and utilization of automatic protection
schemes and definition of restrictive operation regimes should be considered and investigated for the wind
power plants above 100MW. Such operation regimes and solutions should be proposed and evaluated by
technical studies and secured by socio-economic considerations. Establishment of reactive power
compensation units and proposals of the right locations in the 60 kV distribution system should also
be considered and investigated by dynamic voltage studies.


Learning objectives
The dynamic voltage stability study has shown ability to integrate between 50MW and 100MW
additional wind power in the power grid of Bornholm by 2020. This figure shall be seen in comparison
to the island’s maximum power consumption of 58MW and already commissioned wind power. This figure
shall also be seen in contrast to an earlier proposed limit of approx. 35MW additional wind power,
which is a result of not-dynamic studies at conservative assumptions.


References
[1] V. Akhmatov, J.E. Nielsen, J. Østergaard, A.H. Nielsen, “State-Estimation of Wind Power System of
the Danish Island of Bornholm”, Nordic Wind Power Conference NWPC 2009, September 10-15 2009,
Bornholm, Denmark.
[2] "Large-scale offshore wind power plants in Denmark - Revision of scenarios for wind power plants' locations" -
“Stor-skala havmølleparker i Danmark – Opdatering af fremtidens havmølleplaceringer”,
Danish Energy Authority - Energistyrelsen, April 2011, in Danish.