electrical infrastructure design considerations david flood head of electrical systems, forewind...
TRANSCRIPT
Electrical Infrastructure Design Considerations
David FloodHead of Electrical Systems, Forewind
Stakeholder Workshops, April 2010
Starting points for design (1)
Approximate “Footprint” of offshore wind-farm location – from offshore exercise
Onshore connection point to UK Transmission Network• Location, Timing for this point set by National Grid• Developer has modest impact on choice of onshore
connection location
Forewind must develop the optimum connection strategy to link together these
two points
Starting points for design (2)
UK Transmission Network
National Grid
V= 400kV AC
Turbine Arrays
Developer
V= ??? AC
NG
Su
b-S
tatio
n
Technical• Distance to existing grid or possible
connection point• Voltage level at existing grid (typically
400kV)• Available capacity on grid and at
connection point• Electrical losses Cost Environmental issues Visual impacts Health and Safety
Starting points for design (3)
UK Transmission Network
National Grid
V= 400kV AC
Turbine Arrays
Developer
V= ??? AC
NG
Su
b-S
tatio
n
Cooperation and dialogue• Grid companies• Land owners• Authorities• Technology suppliers
Collecting the power from the turbines Typical inter array layout
Turbine Arrays
Developer
V≥33kV AC
Off
sho
re C
olle
cto
r S
tatio
n
Radial configuration• Most common solution• Adopted from onshore wind farms• “String” a number of turbines along a 33kV cable• Approximately 8 turbines on each array string
(max. 40MW)
Power collection added
UK Transmission Network
National Grid
V= 400kV AC
Turbine Arrays
Developer
V≥33kV AC
OffshoreCollection
Developerthen OFTO
V≥132 kV AC
Off
sho
re C
olle
cto
r S
tatio
n
NG
Su
b-S
tatio
n
Next step:• Connection to shore
Exporting the power to shore (1)
Two main choices of transmission to shore exist:• DC – Direct Current always flows in the same direction, but it
may increase and decrease• AC – Alternating Current flows one way, then the other way,
continually reversing direction
Mains electricity in the UK has a frequency of 50Hz AC
DC more suitable for transmission over long distances• Lower losses• Fewer cables• But requires large converter stations at each end
HVDC converters - What do these look like? [courtesy of ABB]
BorWin1 offshore converter station (400MW)
Murraylink HVDC Light, Berri station (220MW)
Power transmission added
UK Transmission Network
National Grid
V= 400kV AC
Turbine Arrays
Developer
V≥33kV AC
OffshoreCollection
Developerthen OFTO
V ≥132kV AC
Export Cable and DC Conversion
Developer then Offshore Transmission Owner (OFTO)
V= +/-320kV DC
Ca
ble
La
nd
fall
On
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ab
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On
sho
re C
on
vert
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Sta
tion
Off
sho
re C
ab
le R
ou
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Off
sho
re C
on
vert
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Sta
tion
Off
sho
re C
olle
cto
r S
tatio
n
NG
Su
b-S
tatio
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Cost/risk/consenting considerations in route selection (1)
Offshore AC array cables• Minimise array string lengths • Minimise losses• Avoid crossing array strings with export cable• Scour can cause lengths of hanging cable (risk of damage)
Offshore DC export cables• Minimise cable length if possible • Minimise number of crossings (pipelines, other cables etc)• Pair of DC cables can be “bundled” into single export cable• Need to have consented “corridor” to allow cable route to
deviate around archaeology, sensitive sites etc• Avoid areas where potential for damage to cable from
fishing/shipping activity
Cost/risk/consenting considerations in route selection (2)
Landfall point• Preferably chosen to minimise overall export distance• Focus on consentability of location to reduce cost and
consenting burden
Onshore DC export cables• Minimise cable length where possible – capital cost• Minimise onshore crossings – railways, rivers etc. All add
cost, time and consenting burden
Onshore converter station• 120m x 60m x 23m footprint (approx.), with associated impact• Needs to be in relatively close proximity to National Grid
Transmission Network connection
DESIGN EXERCISE
Inputs:• Wind-farm locations for each table informed by Offshore
Exercise output• Connection points to transmission network given by “
National Grid Offshore Development Information Statement”
Design the best connection routes to:• Minimise overall cable lengths• Ensure consentability of chosen route (onshore sub-station,
onshore cable route, landfall point, offshore cable route)• Minimise number of crossings (cables, pipelines, rivers,
railways etc)• Avoid sterilising areas of Dogger Bank Zone for future
development with chosen export cable route