GBSQSS recommendations for offshore transmission networks GBSQSS Sub Group OTEG 29 September 2006 1
Contents � Background � Methodology � Scope of offshore transmission � Cost benefit analysis � Offshore transmission voltage requirements � Recommendations � Further work 2
Background � Ofgem scoping document published in April 2006 � OTEG established � GBSQSS sub-group of OTEG set up to review existing GBSQSS and test relevance to offshore transmission networks � This presentation sets our GBSQSS sub-group assessment of the GBSQSS and its recommendations � X meetings (man hours) � X thousand studies 3
Methodology � Consider GBSQSS and identify areas that require review � Cost benefit analysis - in line with existing GBSQSS and ER P2/6 � Formulation of working assumptions � Consideration of assets likely to have an impact on outcome of cost benefit analysis � Creation of network models for assessment � Population of network models with real data � Carry out analysis and present back to sub-group at each meeting � Test key input variables for the value at which the conclusion changes 4
Scope of offshore transmission Shore Generator Onshore Offshore system Transmission (Transmission system or Distribution) Offshore Grid Entry Point Onshore Grid Entry Point or User (offshore platform) System Entry Point Generator Offshore TO Onshore TO /DNO 5
Scope of offshore transmission Central high voltage High offshore Low platform voltage voltage assets assets Offshore Windfarm transmission network Offshore Preferred option platform transformer circuits 6
Cost benefit analysis � Network models � Single / shared AC connections � Single / shared DC connections � Windfarms considered � Up to 1500MW � Up to 100km from shoreline � Sensitivity assessment of input parameters to test robustness of recommendation 7
Offshore transmission voltage requirements � Assessment of existing arrangements � At onshore connection point of offshore transmission network to onshore electricity network � At offshore connection point of generator to offshore transmission network � Outline possible options � Consideration of voltage limits at connection of offshore network to onshore network � Consideration of voltage limits at offshore platform � Comparison of options and provide recommendations 8
Offshore transmission voltage requirements Offshore generator Onshore TO or DNO Offshore TO Onshore Offshore Shore substation substation Offshore windfarm A B Onshore Grid or User System Generator has to meet Existing onshore GB Grid Code SQSS voltage requirements. requirements apply. Recommended that Grid Code, CC.6.3.2(b) CC.6.3.2(c) and CC.6.3.8(c) apply at New voltage limits set for offshore platform onshore/offshore interface: • Reactive power capability • Voltage control Offshore SQSS recommendations 9
Recommendation – Offshore platform � For a single wind farm connection � Platform capacity should be planned to accept the full output of the windfarm with no equipment loadings exceeding their pre-fault rating. For AC connections; for wind farms with an export capacity of � 120MW or greater, following the outage (planned or unplanned) of a single offshore transmission transformer circuit, the reduction in transformer circuit capacity should not exceed 50% of the export capacity of the windfarm connected. � For DC connections; for outages (planned or unplanned) of a single offshore platform DC converter module, the loss of power infeed shall not exceed 1000MW. 10
Recommendation – Offshore platform � For a multiple windfarm connections � Transformer capacity should be planned to accept 90% of the cumulative installed capacity of the windfarms connected, with no equipment loadings exceeding their pre-fault rating. For AC connections; for wind farms with an export capacity of � 120MW or greater, following the outage (planned or unplanned) of a single offshore transmission transformer circuit, the reduction in transformer circuit capacity should not exceed 50% of installed transformer capacity . � For DC connections; for outages (planned or unplanned) of a single offshore platform DC converter module, the loss of power infeed shall not exceed 1000MW. 11
Recommendation – AC platform Single windfarm connection 100MW windfarm LV assets For wind farms with an export capacity of 120MW or greater, Platform should be designed such following the outage (planned that the High Voltage and Low or unplanned) of a single Voltage terminals of the platform offshore transmission transformer circuits are 1 x 100MW transformer circuit, the rated unit interconnected to allow for full reduction in transformer circuit flexibility of use of all assets capacity should not exceed housed upon it. 50% of the export capacity of the windfarm connected. HV assets Offshore Single transmission offshore cable platform Substation network configurations for illustration only 12
Recommendation – AC platform Single windfarm connection 500MW windfarm For wind farms with an export LV assets capacity of 120MW or greater, following the outage (planned Platform should be designed or unplanned) of a single such that the High Voltage and offshore transmission Low Voltage terminals of the transformer circuit, the platform transformer circuits are 2 x 250MW reduction in transformer circuit rated units interconnected to allow for full capacity should not exceed flexibility of use of all assets 50% of the export capacity of housed upon it. the windfarm connected. HV assets Offshore Single Substation transmission offshore cable configurations for platform network illustration only 13
Recommendation – AC platform Multiple windfarm connection 50MW 50MW Transmission transformer capacity should be planned to accept 90% of the cumulative Offshore transmission circuit installed capacity of the windfarms connected, with no equipment loadings exceeding their pre-fault rating. For windfarms with a cumulative installed capacity of above 120MW, following the 1 x 90MW rated units outage (planned or unplanned) of a single offshore transmission transformer circuit, the reduction in transformer circuit capacity should not exceed 0.5 * X% of cumulative installed capacity of the windfarm/s connected. Offshore transmission circuit Shoreline Onshore grid entry point Substation configurations for illustration only 14
Recommendation – AC platform Multiple windfarm connection Transmission transformer 500MW 500MW capacity should be planned to accept X% of the cumulative installed capacity of the windfarms connected, with no Offshore transmission circuit equipment loadings exceeding their pre-fault rating. For windfarms with a cumulative installed capacity of above 120MW, following the outage X=90% in this example 2 x 450MW (planned or unplanned) of a rated units single offshore transmission transformer circuit, the reduction in transformer circuit capacity should not exceed 0.5 * X% of cumulative installed capacity of the windfarm/s connected. Offshore transmission circuit Shoreline Substation configurations for illustration only Onshore grid entry point 15
Recommendation – Network capacity � For a single windfarm connection � Transmission cable circuit capacity should be planned to accept the full output of the windfarm with no equipment loadings exceeding the pre-fault rating. � For multiple windfarm connections � Transmission cable circuit capacity should be planned to accept X% of the cumulative installed capacity of the windfarms connected to it, with no equipment loadings exceeding their pre-fault rating � Following the outage of a single offshore transmission cable circuit, the reduction in cable circuit capacity should not exceed 1500MW i.e. can allow up to 1500MW to be connected to a single transmission cable circuit. 16
Recommendation – Network capacity Single windfarm connection Offshore 500MW platform Following the outage of a single offshore transmission circuit, the reduction in circuit capacity should not exceed The transmission circuit 1500MW i.e. can allow up to capacity should be planned to 1500MW to be connected to Single accept the full output of the a single transmission circuit. 500MW windfarm with no equipment circuit loadings exceeding the pre- fault rating Onshore grid 17
Recommendation – Network capacity Multiple windfarm connection 500MW 500MW Local offshore platform Following the outage of a The circuit capacity should be planned single offshore transmission to accept 90% output of the windfarms circuit, the reduction in circuit connected to it, with no equipment capacity should not exceed loadings exceeding their pre-fault 1500MW i.e. can allow up to Master offshore platform rating. 1500MW to be connected to a single transmission circuit. Single 900MW rated circuit Shoreline Onshore grid entry point 18
Issues for OTEG consideration � DNO ‘sandwich’ � Assessment of demand connected to offshore transmission networks � The consideration of generating plant with a higher annual capacity factor(e.g. offshore CCGT, tidal etc) should be considered � Access rights, compensation arrangements and transmission charging require review 19
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