Experience on Technical Solutions for Grid Integration of Offshore Windfarms

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2 Experience on Technical Solutions for Grid Integration of Offshore Windfarms Liangzhong Yao Programme Manager AREVA T&D Technology Centre 18 June 2007, DTI Conference Centre, London

3 Agenda The 90MW Barrow Offshore Wind Farm The 400MW Sandbank 24 Offshore Wind Farm 3 Experience on Offshore Windfarms 3

4 1. The 90MW Barrow Offshore Wind Farm In the UK 4 Experience on Offshore Windfarms 4

5 The 90MW Barrow Offshore Wind Farm 132kV Cable Wind farm Offshore Platform 5 Experience on Offshore Windfarms 5

6 The 90MW Barrow Offshore Wind Farm Connect 30, VESTAS V-90 3MW Wind Turbines (DFIGs) to the Grid System via an offshore sub-station Voltages: 1kV/33kV/132kV Cables Offshore (3-core) 33kV 120mm2, 300mm2, 22.3kM 132kV 300mm2, 27km, offshore Onshore (1-core) 132kV 400mm2, 2.6km, onshore Ensure the connection meets the requirements of the connection agreement 6 Experience on Offshore Windfarms 6

7 The Key Connection Requirements The steady state reactive power flow at the Heysham substation connection point shall be unity power factor +/- 5MVAr for active power flow in the range of 0 and 90MW into the NGT system. Voltage Operation Range 33kV 95% - 105% 132kV 80% - 110% Q =0 <±5MVAr Grid The system shall remain stable and connected to the system without tripping for a solid three phase fault or any unbalanced short circuit for a total fault clearance time of up to 140ms Wind turbine may trip 7 Experience on Offshore Windfarms 7

8 Design Solution Reactive Power Capability Designed by Vestas V-90 +Qg +Qg Cosph=0.98 1p.u. Pg 1p.u. Pg -Qg Voltage Control 120MVA Transformer with a tap changer range: -18% / +12% Reactive Power Compensation Installation of a 132kV 24MVAr permanently connected reactor at Heysham Grid connection point Installation of 2x5MVAr switchable shunt capacitors on the 33kV offshore substations -Qg Cosph=-0.96 Reactive Power Capability Considered for Vestas V-90 8 Experience on Offshore Windfarms 8

9 Design Solution Other Issues Considered/Studied Cable Rating Load Flow Losses Three Phase and Single Phase Fault Levels Transient Stability and Fault Ride Through Capability Insulation Co-ordination Ferro Resonance Transients Due to Capacitor Switching Circuit Energisation/De-Energisation Harmonic Cable Thermal Study, etc 9 Experience on Offshore Windfarms 9

10 Some of Case Studies A Example of Reactive Power Compensation Less than +/- 5MVAr Pgneration=100% 10 Experience on Offshore Windfarms 10

11 Some of Case Studies Fault Ride Through (a) Voltage Dip P Q (b) P and Q at the Connection Point Wind Farm Ride through the Fault (c) WTG Speed Dynamic Responses for a 3-Phase Fault at the Connection Point 11 Experience on Offshore Windfarms 11

12 Connection at Heysham 12 Experience on Offshore Windfarms 12

13 Offshore Substation Overview Length 23m Width 15m Height 10m Weight 440 tonnes Modularised equipment 33kV Board - including protection B 33/132kV 120MVA Transformer with OLTC 132kV GIS Relay and control panel suite room A LVAC and DC plant room (incs UPS for navigation lights) C 225kVA standby diesel generator Refuge, mess and workshop module D 5MVAr Shunt Capacitor bank modules E HVAC systems INERGEN/Water mist fire suppression system. A 13 Experience on Offshore Windfarms 13

14 2. The 400MW Sandbank 24 Offshore Wind Farm in North Sea, Germany 14 Experience on Offshore Windfarms 14

15 Introduction Sandbank 24 Offshore Wind Farm 80 Turbine Generators (5MW per turbine,dfig, Repower) 400MW Wind Generation Estimated Circuit Length approximately 80kM offshore cable for wind farm, and 190kM Offshore + 50kM Onshore cables for connection Water Depth: 25m to 30m Connection Point: E.ON Brunsbüttel 7 phase projects in the region, and maximum WTGs to be installed= Experience on Offshore Windfarms 15

16 Introduction Wind Farm Location Sandbank 24 Sandbank Experience on Offshore Windfarms 16

17 Introduction Wind Farm Layout Grid Connection Point Offshore substation 17 Experience on Offshore Windfarms 17

18 Introduction Scope of Grid Connection Option Studies Technical feasibility and availability in terms of manufacturing feasibility & availability and meeting the E.ON connection requirements Costing optimisation of each connection, including a summarised cost breakdown for each solution 18 Experience on Offshore Windfarms 18

19 Grid Code Requirements for Connection Some Key Technical Requirements Reactive Power /Voltage Control Range For example, pf lagging to 0.95 leading depending on voltage level Fault Ride Through Capability Solid grid fault up to 150ms Power / Frequency Characteristic Frequency Control Power Quality Harmonics, Flicker Others Wind turbine may trip Ref: E.ON Netz GmbH, "Grid Code: High and Extra High Voltage", August Experience on Offshore Windfarms 19

20 Connection Options AC Connection + Switchable/Permanently Connected Capacitors/Reactors Fixed shunt inductors to compensate for Cable Capacitance Transformer tap changer to control Q and V AC Connection + Dynamic Reactive Compensation (FACTS) SVC STATCOM Voltage Source HVDC (VS HVDC) Line Commutated HVDC (LC HVDC) Needs Synchronous Compensator or STATCOM 20 Experience on Offshore Windfarms 20

21 Connection Options DFIG Wind Farm Connection Connection type AC AC + SVC or STATCOM VS HVDC LC HVDC Doubly Fed Induction Generator or Direct Drive Synchronous Generator Risk of Harmonic resonance High charge current for long cables V & Q control depending on WTG converter rating Risk of Harmonic resonance High AC charge current for long cables V & Q control depending on WTG converter & SVC or STATCOM rating Switching Losses P, V & Q control No AC charge current P Control but needs STATCOM or Synchronous Compensator for V&Q control No AC charge current Lowest losses 21 Experience on Offshore Windfarms 21

22 Option Proposals and Case Studies Proposed Connection Options 150kV AC 220kV AC AC Connection 450kV Mono-Polar HVDC ±240kV Bi-Polar HVDC Conventional HVDC Connection ±150kV VSC HVDC 22 Experience on Offshore Windfarms 22

23 Option Proposals and Case Studies An Example of 150kV HVAC Connection Option One of Problems with HVAC Connection 6kV 1 9 Group 1: 50MW 2 10 Group 2: 50MW 3 11 Group 3: 50MW 4 12 Group 4: 50MW 5 13 Group 5: 50MW 6 14 Group 6: 50MW 7 15 Group 7: 50MW kM Offshore cable 50kM Onshore cable 33kV 6kV Group 8 50MW Offshore Substation kV 170kV kV 3x1x1200mm2 KQ 3x1x1200mm2 KQ kM 250MVA 18% L18 L37 150kV kM 250MVA 18% L42 L61 SVC/STATCOM Connection Point 150kV 380kV Brunsbuttel 250MVA Grid 18% 250MVA 18% 150kV Onshore/Grid Substation Voltage Magnitude in p.u. (150kV HVAC Connection) kM kM Offshore Cable 190kM Offshore Cable Onshore 1.12 Cable % Wind Generation % Wind Generation % Wind Generation B18 B19 B20 B21 B22 B23 B24 B25 B26 B27 B28 B29 B30 B31 B32 B33 B34 B35 B36 B37 B38 B39 B40 B41 B42 B43 B44 B45 B46 B47 B48 B49 B50 B51 B52 B53 B54 B55 B56 B57 B58 B59 B60 B61 B62 B63 B64 B65 Bus Name (Location) 50kM Onshore Cable Voltage Rise along with Cable Circuit It is the same as 220KV HVAC connection 23 Experience on Offshore Windfarms 23

24 Option Proposals and Case Studies An Example of HVDC Connection Option- 450kV Mono-Polar HVDC Connection Point Brunsbuttel 380kV Grid 50kM Onshore Cable 190kM Offshore Cable 500MVA 18% AC Reactive Power Filter Compensator 450kV 1x800 mmsq Cu Cable 24kV 1x800mmsq Return Cable 400MW, 915A Monopolar HVDC Link 450kV 1x800/1390 mmsq Offshore Cable with Integrated Return 5MW 6/33kV 1kM 33kV 500MVA 18% AC Filter Reactive Power Compensator Group Group Group Group4 Group3 Group Group5 Group1 24 Experience on Offshore Windfarms 24

25 Technical Performance Comparison Losses Comparison of Various Options P Loss (%) HVDC Power Losses (%) of Various Options 60% 50% 40% 30% 20% 10% AC and VSC HVDC VSC HVDC Bi-Polar HVDC Mono-Polar HVDC 150kV HVAC 220kV HVAC 0% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Wind Generation Level (%) Assume: Transformer copper loss: Transformer iron (no-load) loss: LCC HVDC Converter loss: VSC HVDC Converter loss: per converter (CIGRE) per converter (CIGRE) per converter (CIGRE) Pg 25 Experience on Offshore Windfarms 25

26 Conclusions Technical solutions for large wind farm connection can be AC Connection AC + FACTS LCC HVDC Connection VSC HVDC connection For 400MW Sandbank 24 offshore wind farm, both LCC HVDC and VSC HVDC technical solutions are very attractive options LCC HVDC - low power losses, increased availability, and large power transfer capability VSC HVDC Capability of P &Q control to meet the grid code requirement To reach an engineering design solution for a wind farm connection with a grid, a number of further studies need to be done to identify the best technical and cost-effective solution 26 Experience on Offshore Windfarms 26

27 Thank you for your attention!