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)
Contents
 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
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-2.3-93 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-2.3-93 wind turbines
 Total capacity is 30 MW
 Karnice Wind Farm is connected
directly to the distribution
network
Offshore Wind Farm
- Horns Rev 2 Offshore Wind Farm
 The biggest offshore wind
farm in the world
 Situated by the west coast
of southern Denmark
 The wind farm consists 91
SWT-2.3-93 wind turbines
 Total capacity is 210 MW
 Horns Rev 2 is connected to the network by
100 km HVAC submarine and underground cable
source: Energinet.dk
Models of Wind Farm Components
 High and Medium Voltage Cables
 Wind Turbine and Park Transformers
 Shunt Reactors
 Capacitor Banks
 External Network
Models of Wind Farm Components
- Medium and High Voltage Cables
Power Cable Impedance
 Lumped Π and T models
ZT
Magnitude |Z| [ ]
 Equivalent Π model
40
30
Z eq
20
10
 Medium voltage cables
equivalent impedance
0
calculated based on aggregated
100
model
 Frequency of interest:
50Hz – 3 kHz
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
4
x 10
50
Angle Z [ ]
 Approximation of the skin
effect using correction
factors
Z
0
-50
-100
0.5
1
1.5
2
2.5
3
Frequency f[Hz]
3.5
4
4.5
5
4
x 10
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
 11th and 13th 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
Thank You