Download Network connection issues for offshore wind farms in UK waters

Some electrical connection
design issues for offshore
wind farms
Paul Gardner, Helen Snodin, & Nigel Scott
Garrad Hassan and Partners
[email protected]
Presentation Rationale
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Most UK projects quite advanced
Grid connections and costs known
Issues of design choices
Unknowns ?
Electrical Design
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Can be split into 3 key areas:
Offshore array
Transmission to shore
Grid connection
will concentrate on the latter two.
Some Electrical Design Issues
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Subsea vs land cable
33kV vs 132kV transmission to shore
Export security
Parallel 132/33kV transformers
Teed vs looped vs busbar connections
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Grid Code changes
Electrical Design Diagram
Onshore
Offshore
Existing 132kV
grid line
Wind turbine
Wind turbine
transformer
Other wind turbines
132/33kV
transformer
132kV switch
circuit breaker
33kV cable
onshore
33kV cable
to shore
33kV submarine cable
within array
132kV cable
Tee or loop
connection ?
Single or double
transformer
arrangement ?
Continue with
submarine cable
onshore ?
Offshore transformation
to 132kV or continue at
33kV ?
Arrangement of
offshore array ?
Subsea vs Land Cables
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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 !
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Onshore
Subsea cables can be used but only worth
considering for short and simple routes.
Key issues are costs and practicability
33kV vs 132kV Transmission
to Shore
Item
Cable
Cable installation
Power losses
Substation
Power factor correction
O&M
Other costs / risks
Highest Cost
132kV
33kV
£
£
£
£
£
£
£
Export Security
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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
Cost of Lost Production
£1.2k
£29k
£206k
£412k
Time
1 hour
1 day
1 week
2 weeks
Export Security - Tee & Loop
Existing grid line
Circuit
breaker/switch
Wind farm
Tee connection
Loop connection
arrangement
arrangement
Export Security
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Single or double 132/33kV transformers
One transformer = all eggs in one basket
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
Grid Code Changes
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Compliance in full or in part mandatory
New Grid Code due in 2002
Possible requirements
Control of real and reactive power
Frequency response
Voltage regulation
Stability
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Implications - more cost ?
Summary
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Impossible to cover all the issues,
design choices and best practices
Hopefully raised awareness of one or
two issues
The answers are often project specific