Wind Farm Structures Impact on Harmonic Emission and Grid Interaction Harmonics in Large Offshore Wind Farms Łukasz Kocewiak (DONG Energy) Jesper Hjerrild (DONG Energy), Claus Leth Bak (Aalborg University)

Onshore Wind Farms Karnice Wind Farm Offshore Wind Farms Horns Rev 2 Offshore Wind Farm Models of Wind Farm Components Harmonic Impedance Karnice Wind Farm Impedance Plots Horns Rev 2 Impedance Plots Results Comparison Harmonic Level at Connection Point Conclusions Contents

Analysed Wind Farms Horns Rev 2 and Karnice Wind Farm Wind farms built and owned by DONG Energy A/S Two different wind farms: onshore and large offshore Equipped with the same SWT wind turbines Connected to completely different networks Wind turbines are equipped with full-scale converters

Onshore Wind Farm - Karnice Wind Farm Onshore wind situated in the north part of Poland The wind farm consists 13 SWT wind turbines Total capacity is 30 MW Karnice Wind Farm is connected directly to the distribution network

The biggest offshore wind farm in the world Situated by the west coast of southern Denmark The wind farm consists 91 SWT wind turbines Total capacity is 210 MW Horns Rev 2 is connected to the network by 100 km HVAC submarine and underground cable Offshore Wind Farm - Horns Rev 2 Offshore Wind Farm source: Energinet.dk

High and Medium Voltage Cables Wind Turbine and Park Transformers Shunt Reactors Capacitor Banks External Network Models of Wind Farm Components

Models of Wind Farm Components - Medium and High Voltage Cables Lumped Π and T models Equivalent Π model Medium voltage cables equivalent impedance calculated based on aggregated model Approximation of the skin effect using correction factors Frequency of interest: 50Hz – 3 kHz

Models of Wind Farm Components - Wind Turbine and Park Transformers Harmonic models based on measurements and data provided by manufacturers Models based on frequency sweep analyzer measurements Measurements performed using FRAX FSA within the confines of internal research projects Frequency of interest: 50Hz – 3 kHz

Models of Wind Farm Components - External Network Frequency characteristic at the point of common coupling Different short circuit levels, network configurations considered Frequency of interest: 50Hz – 3 kHz

Harmonic Impedance - Karnice Wind Farm

Harmonic Impedance - Horns Rev 2 Offshore Wind Farm

Results Comparison

Harmonic Level at Connection Point Large wind farms significantly change impedance at PCC Voltage THD much lower during wind farm production 11 th and 13 th voltage harmonics change significantly

Conclusions Offshore wind farms are mainly connected to the transmission network by long HV cables Offshore wind farms have much more components which have influence on overall system impedance Medium voltage cables network is much bigger in offshore wind farms Large offshore wind farms can operate as a power plant and improve power quality at the point of connection Every large wind farm has to be analysed separately

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