1. Some electrical connection design issues for offshore wind farms Paul Gardner, Helen Snodin, & Nigel Scott Garrad Hassan and Partners nigel.scott@glasgow.garradhassan.co.uk Paul Gardner, Helen Snodin, & Nigel Scott Garrad Hassan and Partners nigel.scott@glasgow.garradhassan.co.uk

2. Presentation Rationale l Most UK projects quite advanced l Grid connections and costs known l Issues of design choices l Unknowns ? l Most UK projects quite advanced l Grid connections and costs known l Issues of design choices l Unknowns ?

3. Electrical Design l Can be split into 3 key areas: l Offshore array l Transmission to shore l Grid connection -will concentrate on the latter two. l Can be split into 3 key areas: l Offshore array l Transmission to shore l Grid connection -will concentrate on the latter two.

4. Some Electrical Design Issues l Subsea vs land cable l 33kV vs 132kV transmission to shore l Export security -Parallel 132/33kV transformers -Teed vs looped vs busbar connections l Grid Code changes l Subsea vs land cable l 33kV vs 132kV transmission to shore l Export security -Parallel 132/33kV transformers -Teed vs looped vs busbar connections l Grid Code changes

5. Electrical Design Diagram

6. Subsea vs Land Cables l Offshore -33kV - use either EPR submarine cables or XLPE cable with additional waterproofing -132kV - use XLPE cables -Better electrical insulator -Sealed in watertight lead sheath - not land cable ! l Onshore -Subsea cables can be used but only worth considering for short and simple routes. -Key issues are costs and practicability l Offshore -33kV - use either EPR submarine cables or XLPE cable with additional waterproofing -132kV - use XLPE cables -Better electrical insulator -Sealed in watertight lead sheath - not land cable ! l Onshore -Subsea cables can be used but only worth considering for short and simple routes. -Key issues are costs and practicability

7. 33kV vs 132kV Transmission to Shore

8. Export Security l Teed vs Loop vs Busbar connections -Capital cost vs improved export security against -grid faults, -operations and maintenance outages -E.g. 100MW at £0.035/kWh and 35% load factor l Teed vs Loop vs Busbar connections -Capital cost vs improved export security against -grid faults, -operations and maintenance outages -E.g. 100MW at £0.035/kWh and 35% load factor

9. Export Security - Tee & Loop

10. Export Security l Single or double 132/33kV transformers l One transformer = all eggs in one basket l Two transformers -Extra capital cost -Improved security against transformer failure -new transformer or repairs could take months -failure rates are low -reduced export depending on transformer rating -Higher O&M costs l Single or double 132/33kV transformers l One transformer = all eggs in one basket l Two transformers -Extra capital cost -Improved security against transformer failure -new transformer or repairs could take months -failure rates are low -reduced export depending on transformer rating -Higher O&M costs

11. Grid Code Changes l Compliance in full or in part mandatory l New Grid Code due in 2002 l Possible requirements -Control of real and reactive power -Frequency response -Voltage regulation -Stability l Implications - more cost ? l Compliance in full or in part mandatory l New Grid Code due in 2002 l Possible requirements -Control of real and reactive power -Frequency response -Voltage regulation -Stability l Implications - more cost ?

12. Summary l Impossible to cover all the issues, design choices and best practices l Hopefully raised awareness of one or two issues l The answers are often project specific l Impossible to cover all the issues, design choices and best practices l Hopefully raised awareness of one or two issues l The answers are often project specific