Download SQSS update

DTI / OFGEM OFFSHORE
TRANSMISSION EXPERTS GROUP
SQSS Sub Group
Review of progress and
future work
2 August 2006
Content
• Review of likely boundary between Offshore
Generator and Offshore TO
• Cost benefit analysis
• Work plan
• Data availability and transparency
• Other issues
Offshore Ownership Boundary
•Reason for review
–Need to understand the scope of the offshore
transmission system to understand the required scope
of the offshore security standards
• This assessment has taken into account 4 options
• Each option has been compared to existing onshore
arrangements, and existing CUSC, STC and charging
methodology definitions.
• More detailed paper to be made available for wider
consultation.
Options considered
Option 4; TO to own up to the individual
wind turbine generator transformer.
Windfarm
electrical system
Windfarm
electrical system
Option 3; TO to own up to the disconnector on
the busbar side of the circuit breaker on the
incoming windfarm circuit
33kV
assets
Option 2; TO to own up to the transformer LV
disconnectors
Single
offshore
platform
132kV
assets
Offshore
transmission
system
Option 1; TO to own up to the transmission voltage
busbar clamps on the platform transformer circuit
Initial Thoughts
• Option 3 is recommended as it:
– Best facilitates competition in generation
– Simplifies ownership of offshore platforms
– Allows the offshore TO to provide Users with a
consistent level of security
• Option 1 could be considered but provides
less benefits than Option 3 if more than
one Offshore Generator is connected
• Options 2 and 4 are not recommended
Initial Thoughts
• Sub-group intends to develop a detailed paper
explaining the recommendation
• Sub-group has assumed that the default
offshore ownership boundary will be as its
recommendation (Option 3)
• Main Impacts:
– Transformer circuits will be included within the
security standards for offshore transmission
– Assumption will require a review of the consequential
impact on Grid Code, access rights and charging
methodology
Cost-Benefit Analysis
•Concept
•Scope
•Example configurations
•Work progress and key results
•Proposed format of SQSS for offshore
transmission
Concept of cost-benefit analysis
Cost
Total Cost
Cost of
curtailed
wind energy
and losses
Investment
&Maintenance
Costs
Optimal network
Network
Capacity and
Redundancy
Scope of cost-benefit analysis
• Offshore networks
– Switchgear reliability, installation cost, platform cost,
ratings, maintenance requirements
– Cable reliability, installation cost, maintenance
requirements, ratings, electrical parameters
• Transmission mode (AC vs DC)
– Compensation requirements
– Losses
• Windfarms
–
–
–
–
Wind resource characteristics
Typical turbine ratings, availability, cost
Windfarm size
Windfarm distances from shore
• Future value of energy and ROCs
• Impact on onshore system operation
– Additional reserve costs
Examples of single AC connections
Windfarm electrical system
Windfarm electrical system
33 kV
33 kV
132 kV
220 kV
Shoreline
132 kV
220kV
Onshore network
Onshore network
Example of a shared AC
connections
33 kV
33 kV
33 kV
132 kV
132 kV
132 kV
132 kV
400 kV
400 kV
Onshore transmission network
Example of a shared DC
connection
33 kV
33 kV
33 kV
132 kV
132 kV
132 kV
132 kV
AC
DC
AC
DC
AC
DC
DC
AC
DC
AC
400 kV
400 kV
DC
AC
275 or 400 kV
On-shore transmission network
Progress and key results
• Methodology for the evaluation of cost and reliability
performance of alternative offshore transmission
configurations has been developed
• Key differences between offshore and onshore networks
– Significantly higher capex requirements
– Technology constraints
– Wind generation operates at lower load factors than
conventional plant
• Analysis of a range of connection types suggests that
generally lower levels of redundancy can be justified for
offshore transmission networks when compared with
onshore transmission networks
– Justifiable levels of redundancy will be influenced by the size of
the wind farm and its distance from shore
– Initial analysis suggests significant benefits in providing flexibility
at the platform and interconnections between offshore platforms
in close proximity
Illustrative results
Wind farm
size (MW)
• Numerical values
shown are indicative
ONLY.
• Studies are NOT
complete and key
assumptions and
electrical, reliability
and cost data need
validation.
• Comprehensive
sensitivity studies are
yet to be carried out
600
450
300
150
10
50
Distance to shore (km)
Proposed Table form of SQSS for
Offshore Networks/1
Distance from Shore: 10 km
Wind Farm
Capacity
Range of Power
Network Capability to be Restored
Available Network
Capacity Following
First Circuit Outage
Available Network
Capacity Following
Second Circuit Outage
Up to
150MW
Between 150MW
and 300MW
0
NIL
X1
NIL
Between 300MW
and 450MW
Above 450MW
Y1
Z1
U1
V1
Proposed Table form of SQSS for
Offshore Networks/2
Distance from Shore 50kM
Wind Farm
Capacity
Network Capability to be Restored
Range of Power
Available Network
Capacity Following
First Circuit Outage
Available Network
Capacity Following
Second Circuit Outage
Up to
300MW
Between 300MW
and 450MW
Between 450MW
and 800MW
Above 800MW
0
NIL
X1
NIL
Y1
Z1
U1
V1
Work plan
Work plan and key dates
• Further develop the cost-benefit evaluation models (by 14
August)
–
–
–
–
Take account of the impact of losses
Quantify the impact of diversity in the windfarm output
Take account of the impact of reactive power effects
Develop models further and carry out sensitivity analysis
• Carry out cost-benefit studies and propose Draft Tables and
Processes for forming SQSS for offshore transmission
networks for review by the sub-group (by 24 August)
• Submit draft SQSS Generation Connection Criteria for
offshore transmission networks to OTEG for consideration (31
August)
• Carry out detailed sensitivity analysis.
• Re-assess and refine draft SQSS Generation Connection
Criteria for offshore transmission networks (30 September)
• Proposed workplan discussed at subgroup meeting on
28/07/06
Data Availability and
Transparency
Data availability
• The study work is conditional on receipt of all data
from suppliers and developers
• The sub-group has defined the data requirements
and highlighted the data that has not yet been
provided
• There is risk that the timescales in the work plan
will not be met if this data required is not provided
– The current work plan is contingent on all data being
provided by 14th August.
Transparency of data
• All results of the cost-benefits evaluations should
be re-producible
• All data used in the analysis should be visible
• Some of the cost information and wind data is only
being provided to the DTI Centre for Distributed
Generation and Sustainable Electrical Energy
(under confidentiality agreements).
– It is hoped that suitable anonymous, generic,
representative data can be produced from project
specific data
• Concern is that the sub-group may not be able to
make a recommendation based on the results of
the analysis work if the input data was not
available to them.
Other Issues
Other issues
• Offshore TO/DNO/GBSO Interface
– Sub-group is concerned by the possible implications on the security of
an offshore transmission network connected to the onshore
transmission network via a distribution network.
– Particular concern relates to differences between the design standards
applicable to transmission and distribution networks.
– Sub-group will investigate and provide feedback to OTEG
• HVDC
– Sub-group is considering DC connection options as part of the cost
benefit analysis work
• Paralleling main onshore GB transmission network through offshore
transmission network
– The subgroup is un-aware of any proposed windfarm connection that
will parallel any nodes of the GB transmission system.
• Islands
– National Grid currently developing Commercial Charging arrangements
for Islands connections. Sub group work to concentrate on establishing
optimum offshore network technical solution with any commercial
arrangements to follow.