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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Nysted Offshore Wind Farm (2003)

21-04-235

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21-04-236

Va, Vb, VcIa, Ib, Ic

Va, Vb, VcIa, Ib, Ic

Va, Vb, VcIa, Ib, Ic

Validated transformer model from NOWF

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

Overview of sequential energization of transformers

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9WTx0s 5WTx5s 2WTx2s 1WTx1s

A01 0,1 5,1 6,1 8,1

A02 0,1 5,1 6,1 7,1

A03 0,1 5,1 6,1 6,1

A04 0,1 5,1 4,1 5,1

A05 0,1 0,1 4,1 3,1

A06 0,1 0,1 2,1 3,1

A07 0,1 0,1 2,1 2,1

A08 0,1 0,1 0,1 1,1

A09 0,1 0,1 0,1 0,1

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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Validated model NOWF-> 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

Conclusions

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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.

Discussion

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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.

Acknowledgment

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