Dias nummer 1

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Voltage dip caused by the sequential energization
of wind turbine transformers
I. Arana, J. Holbøll, T. Sørensen, A. H. Nielsen,
O. Holmstrøm, P. Sørensen
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DONG ENERGY Business Model
Power
3
DONG ENERGY Past and future
After the merger, DONG Energy is active in every
link of the energy chain

• Exploration and production of oil and natural gas
• Generation of power at conventional power plants
  and renewable energy plants
• Sales of electricity and gas to end consumers
  including energy saving consultancy services

4
Wind power plants

• Current
• Nysted (132MW)
• Horns Rev (64MW) 
• Barrow (45 MW) 
• Burbo (90 MW)
• Developing
• Horns Rev 2 offshore, Denmark (209 MW) 
• Gunfleet Sands I offshore, UK (108 MW)
• Gunfleet Sands II - offshore, UK (65 MW)
• Walney I - offshore, UK (151 MW)
• Storrun - onshore, Sweden (30 MW)
• Karnice I, onshore, Poland (30MW)
• London Array
• On- and offshore projects in Denmark, Germany,
  UK, Poland, France, Sweden, and Norway
• Almost 80 projects on pipeline
• DONG Energys Social Responsibility Report 07
• By 2020, we will triple our capacity of renewable
  energy to approximately 3,000 MW.
• 500 Wind turbines contract with Siemens Wind Power

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Nysted Offshore Wind Farm (2003)
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GPS synchronized measuring system (2007)
Va, Vb, Vc Ia, Ib, Ic
Va, Vb, Vc Ia, Ib, Ic
Va, Vb, Vc Ia, Ib, Ic
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Validated transformer model from NOWF

• Transformer energization measured and simulated
  currents at WT A09 from 15 ms to 70 ms.

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Overview of sequential energization of
transformers
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Voltage phase angle switching
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Voltage and current at platformVzero A01 to A09
sequence
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Real and reactive power Vzero A01 to A09
Vzero A09 to A01
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Reactive power and voltage

• higher Q are the ones where the energization
  starts in A01
• largest Vdip are the ones with peak voltage
  switching

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Sympathetic current/voltage dip
Vzero A01 to A09 Vzero A09 to A01
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Conclusions

• Validated model NOWF-gt several radial
  energizations using PSCAD
• voltage dip
• switching angle
• number of simultaneously energized transformers
• energizing sequence direction
• wind turbine transformers are switched-in
  independently
• smallest voltage dips, and lowest inrush current
• energizing direction, with 0 and 90 switching
  angle
• starting with A09 the transformer at the far end
  of the cable radial
• starting with A01 at the end of the cable radial
  closest to the wind park transformer
• higher Q are the ones where the energization
  starts in A01
• largest Vdip are the ones with peak voltage
  switching
• The reactive power from the previously energized
  transformers varies every time a transformer is
  energized and it was found that this reaction
  depends on the relative location of the
  transformers
• Standard transformer models PSCAD
• Assess energization voltage dips against the UK
  P28

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Discussion

• Sympathetic reaction from the neighboring
  transformer
• Superimposed effects
• Standard transformer model
• On-going work
• No generalization
• Systematic study for each wind farm
• Nine wind turbine transformers energized
  simultaneously
• Not even 2 voltage dip was present.
• Individual transformer energization in zero
  voltage switching
• Lowest voltage dip of 0,26
• Voltage dips can be assessed by detailed
  simulation studies
• Questionable if the UK P28 for voltage dips are
  at all relevant for wind farms given that wind
  turbine transformers are switched at worst a few
  times a year.

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Acknowledgment

• This work is made as part of an Industrial Ph.D.
  project supported by the Danish Ministry of
  Science, Technology and Innovation, project
  number 08-041566.
• The switching transient measurements used in this
  study were obtained in the project titled
  Voltage conditions and transient phenomena in
  medium voltage grids of modern wind farms,
  contract 2005-2-6345, supported by the Danish TSO
  Energinet.dk.