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ISLES

Route Development and Cost Estimation Report

APPENDIX B ONSHORE ELECTRICAL INFRASTRUCTURE ASSESSMENT

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INTRODUCTION

The connection of renewable generation into the onshore transmission systems faces many challenges, and one of the challenges is the limited transmission capacity available for power transfer from the points where the renewable generation is connected to load centres. This is especially the case when a number of large offshore renewable generation resources seek connection to the same network at or close to the same time period. For the purpose of developing a feasible connection scheme for ISLES offshore renewable generation, the initial requirement is to establish a best estimate of the transmission infrastructure status of onshore transmission systems for the time when the ISLES offshore renewable generation is expected to be connected. This is necessary both to identify the competing resources that are likely to seek connection to onshore transmission networks, but also to establish the network environment into which ISLES must connect, and the value of the energy that it will deliver. It is believed that the ISLES offshore renewable generation could be connected to both the GB and All-Island onshore transmission systems for the timeframe of circa 2020, and the GB onshore system is the main load centre for the ISLES offshore renewable generation export. As a result, the transmission network capacity available in the GB onshore system by 2020 is the primary focus for connection design of the ISLES offshore renewable generation, though the transmission network capacity available in the All- Island onshore systems is crucial as well. The ISLES offshore renewable generation development zone covers the waters off the western coast of Scotland, north coast of Northern Ireland and the Irish Sea. It is believed that onshore transmission networks in Scotland, Northern England, Wales South-west England in the GB onshore system would be the ideal areas for connection of the ISLES offshore renewable generation and for ISLES offshore renewable generation export to the GB onshore system, due to their proximity to most ISLES offshore renewable resources. A number of ISLES offshore renewable resources are located close to the All-Island onshore system; it is believed that the onshore transmission network in the Northwest, Northeast, East, and Southeast of Ireland and in Northern Ireland (NI) would be the ideal area for connection of those ISLES offshore renewable generation resources. This section presents an assessment of the transmission infrastructure capability of both the GB and All-Island onshore systems for the timeframe of circa 2020. The assessment is focussed on the transmission network regions listed above, as they are the key to the connection design of the ISLES concepts. Transmission infrastructure in other areas in the GB and All-Island onshore systems may impact the connection design, for example, deep onshore transmission reinforcements may be required in those areas to increase power transfer capability from the networks where ISLES offshore renewable generation is connected to the load centres. It is not believed that the impact is significant, as those areas are far away from the ISLES offshore renewable resources and direct connection of ISLES offshore renewable generation to the transmission networks of those areas is impractical. The assessment of transmission infrastructure status comprised:

estimation of the generation capacity and generation mix of the onshore systems to meet the maximum demand in winter peak; estimation of the projected winter peak demand levels across the onshore systems; identification of the existing transmission networks, future transmission developments, and proposed network reinforcements for formation of the 2020 transmission networks; an estimation of the capability of key super-grid substations to accommodate new generation connections and an assessment of onshore system power transfer capability across system boundaries though a detailed assessment of power flows.

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The assessment of onshore transmission network capabilities was based upon publicly available information such as the GB Seven Year Statement, ENSG reports, and published transmission forecast statements and development plans from EirGrid and Northern Ireland Electricity. In order to assess the transmission network capacity in the GB onshore system, a detailed load flow model of the full system was developed based on publically available information, and enhanced based on both known projects being implemented such as the Beauly-Denny and Western HVDC link, and other projects detailed in the ENSG report on required transmission upgrades. The assessment was undertaken using transmission planning techniques that take into consideration the requirements of NET SQSS, which is the transmission planning standard for the GB network. It is understood that the generation mix, physical location, and dispatch characteristics will be important factors in identifying new generation connection capability at key super-grid substations and transmission capability across system boundaries and the provision of acceptable security of supply. Extensive system analysis of the All-Island onshore transmission system was also undertaken. However, it is worth highlighting that the All-Island system is more likely to be a net source of onshore renewable generation than a net demand. For this reason, the All-Island system is considered to be severely limited in its ability to accept significant levels of offshore renewable generation from any ISLES network. Nevertheless, the available network capacity has been estimated at various key locations on the All-Island network, based on the voltage level and rating of existing/envisaged transmission infrastructure. This assessment is divided into three main sections.

The first section outlines the estimated generation background in both the GB and All-Island onshore systems for the year 2020 to meet the predicted maximum peak demand of the year. The generation and demand level in the GB onshore system is also the base information which is used to develop a detailed 2020 power system model for transmission network capacity assessment.

The second section presents the onshore transmission network information including the existing transmission network, future transmission developments, and proposed network reinforcements by 2020. The transmission network information in the GB onshore system is the key to the development of the detailed 2020 power system model.

The last section details the resultant transmission network capacity of the two onshore systems, providing supportive information for selection of super-grid substations at which the ISLES offshore renewable generation are likely to be connected to the onshore systems.

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GENERATION AND DEMAND BACKGROUND BY 2020

This section details the assumed generation and demand background which forms the basis for the development of an onshore transmission system model, and from which the transmission network capacity was assessed. The generation and demand background covers generation estimate and load demand growth by 2020 in both the GB and All-Island onshore systems.

2.1

2020 GENERATION BACKGROUND IN GB SYSTEM

The estimation of generation capacity for 2020 in the GB system was based on available information contained in the GB 2009 SYS including the power station generation capacity listed in “Table 3.5 (SYS) – Power Station Transmission Entry Capacities for 2009-10 to 2015-16”, and power generation capacity listed in “Table 3.16 - Transmission Contracted Generation beyond 2015-16”. At the time that the analysis was completed, the 2009 SYS was the latest available version of the document. It is recognised that an updated (2011) SYS is now available, but the background data extracted from the 2009 document remains broadly consistent with that published in the 2011 SYS. We understand that several coal generation and nuclear generating units will be decommissioned before 2020. For the purposes of this transmission network capacity assessment, we assumed that all generation capacity listed in the GB 2009 SYS is available. This assumption results in a conservative (worst-case) assessment of the available transmission network capacity. It is estimated that the generation capacity in the entire GB system will total 113.2 GW by 2020 with onshore and offshore wind renewable generation of 16.9 GW and conventional and other renewable generation of 96.3 GW. The generation mix for 2020 is presented in Figure B2.1 below. Please note that the estimated generation capacity does not include any Round 3 Offshore Wind Developments or Scottish Offshore Wind Exclusivity Agreements approved by the Crown Estate except for Beatrice at 920 MW. The above figures do include most of the Round 2 Offshore Wind Developments except for Walney and West Duddon in western coast waters, and Triton Knoll, Westermost Rough and Dudgeon in eastern coast waters. It is believed that these generation projects will impact the north to south power flow and new generation capacity connected at or along the north south power transfer corridors. Generation capacity in Scotland dominates the north south power flow and has a key influence on the ability of substations along the north south power transfer corridors to accommodate new generation connections. The estimated generation capacity in Scotland for 2020 is therefore an important input to this study. It is expected that generation capacity in Scotland will total 19.9 GW by 2020, with 9.9 GW from wind, 1.5 GW from gas, 3.4 GW from coal, 2.3 GW from nuclear, 0.74 GW from pumped-storage, and 2.0 MW from other renewable generation including hydro, CHP and biomass. The anticipated generation mix in Scotland for 2020 is shown in Figure B2.2 below.

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GB 2020 Generation Mix (MW) 4143

Interconnector

2744

Pumped Storage

3636

Oil

4848

Others

9444

Nuclear

28896

Coal

42607

Gas 16923

Wind

Figure B2.1 – 2020 Generation Capacity Mix in GB System

2020 Generation Mix in Scotland (MW) Interconnector

80 740

Pumped Storage Oil Others

0 1978 2289

Nuclear

3406

Coal Gas

1534 9863

Wind

Figure B2.2 – 2020 Generation Capacity Mix in Scotland The estimated generation background forms the basis of the assessment of transmission network capacity in the GB 2020 onshore system. It should be pointed out, however, that a number of factors may affect the generation background, and these factors, listed below, should be considered in the design of offshore transmission network for connection of the ISLES offshore renewable generation.

Round 3 offshore wind generation developments with a combined capacity of approximately 25.5 GW, and some offshore wind generation developments approved by Crown Estate in Scottish Offshore Wind Exclusive Agreements which are not included in the defined ISLES zone.

Connection of new generation including new CCGT and nuclear generating units.

Introduction of new interconnections to increase power exchange capacity between the GB and All-Island systems and between the GB and European continent systems.

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Decommissioning of existing plants due to age profile, due to requirements of reducing CO2 emissions (for example, decommissioning of some large coal units or all of them to meet the specified CO2 target), or the Large Combustion Plant Directive that aims to reduce acidification, ground level ozone and particles through limiting emissions of sulphur dioxide (SO2), nitrogen oxides (NOx) and dust (particulate matter (PM)).

2020 LOAD DEMAND BACKGROUND IN GB SYSTEM

In the GB onshore system, the main load centre is in England and Wales. The winter peak demand level is typically the most onerous demand condition that generation should have sufficient capacity to meet and that the transmission network should be adequate to accommodate. It is recognised that under some infrequent scenarios i.e. a very windy summer’s day in Scotland with low demand and a baseload of nuclear generation, there may instances of higher circuit loading. However, winter peak demand is the most representative of ‘average’ maximum system capacity. Both increasing demand and new generation connection to the network drive future transmission network development and network reinforcements. The 2020 winter peak demand in the GB system is estimated at the level of 66.3 GW. The level of demand was projected by applying an annual demand growth rate of 1.054% pa on the available demand forecast of 2015/16 which amounts to 62.8 MW and is published in the 2009 GB SYS. The annual growth figure of 1.054% was derived as the mean annual growth applied in the SYS over the period 2009-2016. Additionally, this projection was also applied to demand level at all grid supply points listed in Table E.1.7 - GSP Winter Peak Demand (MW), Generation (MW) and power factor, 2015-16.xls. This demand projection excludes the transmission losses, station load, embedded generation contribution, and power export to the All-Island system via the existing and planned HVDC links. The projected demand level together with the estimated generation capacity in the specified system study zones, which are the main concern of the project, is shown Figure B2.3 below.

Generation & Demand in System Study Zones (MW) 2703

Z17

3818 5490

Z13

11929 8369

Z9

13275 6572

Z8

15197 3161

Z7

7406 3286

Z6

7924 973

Z5

2585 518 631

Z4 55

Z3

1209 663

Z2

3364 541

Z1

4177 0

2000

4000

6000

8000

Zonal Generation

10000

12000

14000

16000

Zonal Demand

Figure B2.3 – 2020 Demand Distribution in Study Zones Figure B2.4 (below) shows the projected demand level and estimated generation capacity in the four specific regions which are of primary interest in the context of the ISLES project. Those regions are specified based on the NGET transmission network boundaries including North-West boundary B1, SHETL-SPT boundary B4, SPT-NGET boundary B6, and NGET Upper North boundary B7. Please

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note that the figures quoted for each specified region includes all system zones above the specified system boundary. For example, the region specified for SPT-NGET boundary B6 includes all six system study zones in Scotland. The regional generation and demand levels shown in Figure B2.4 indicate that significant amount of generation power will flow from the north in Scotland down to the south in England and Wales. Though variation of annual demand growth rate for demand projection may affect the total demand levels, it will not affect the north south power flow patterns as generation capacity of the system dominates the north-south power flow.

9197 NGET North Boundary B7 27296

6036 SPT-NGET Boundary B6 19890

1777 SHETL-SPT Boundary B4 9381

541 North-West Boundary B1 4177

0

5000

10000

Demand Level

15000

20000

25000

30000

Generation

Figure B2.4 – 2020 Generation and Demand Distribution in Specific Regions

2.3

2020 GENERATION AND DEMAND IN THE ALL-ISLAND SYSTEM

The generation background in the All-Island system consists of the existing generation and the planned generation which we believe will be connected to both the Republic of Ireland and the Northern Ireland (NI) onshore transmission systems by 2020. The generation background in the All-Island system was based on transmission network models that were used for the All-Island Grid Study and on publicly available information about anticipated onshore renewable generation developments. It is expected that generation capacity in the All-Island system will total 21.7 GW for 2020 with 6.1 GW in Northern Ireland and 15.6 GW in the Republic of Ireland. The anticipated generation mix in the All-Island system for 2020 is shown in Figure B2.5 below.

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2020 Generation Mix in All Ireland System RoI System

Other Renewables

216.0 500.0 850.0 500.0

Interconnector

Pumped Storage

292.0 0.0 962.1

Coal

Peat

NI System

476.0 338.0 0.0 6349.3

Gas

2566.0 6648.4

Wind

2050.0

Figure B2.5 – Generation Mix in 2020 All-Island System

Peak demand levels in the All-Island system were assumed to be 8.0GW, with 6.0 GW of this in the Republic of Ireland and 2.0 GW in Northern Ireland. The assumption was made based on the AllIsland Grid Study model taking into the impact of difficult economic conditions in recent years. The estimated generation capacity and projected load demand level in All-Island system for 2020 are shown in Figure B2.6. The estimated generation capacity combined with the projected demand levels in the All-Island onshore system suggests that that the onshore system is likely to have more than adequate generation capacity to meet the projected peak demand by 2020 with extra generation power that may be available for export to GB.

2020 Generation and Demand Background in All Ireland System Demand

Generation

2021 NI System 6092.0

5989 RoI System 15655.8

Figure B2.6 – Generation Capacity and Demand Level in 2020 All-Island System

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B3. EXISTING AND INFRASTRUCTURE

PLANNED

TRANSMISSION

NETWORK

This section provides information on transmission network background in both the GB and All-Island systems. The transmission network background includes existing transmission network and future transmission developments for the time frame of circa 2020 when the ISLES offshore renewable generation is likely to connect to the onshore systems. The transmission network background together with the generation background and the projected load demand, form the basis upon which transmission capability of the network is assessed and additional generation connection capability at substations is identified.

3.1

GB TRANSMISSION SYSTEM

Information on the existing transmission network and on the future transmission network development up to 2015 was extracted from the GB 2009 SYS. Information on the proposed network reinforcements from 2006 to 2020 was extracted from the ENSG report. The reinforcements include construction of new super-grid substations, expansion of existing super-grid substations, installation of new HVAC and HVDC transmission circuits, and upgrade and up-rating of existing transmission circuits. A detailed system model was constructed based on the available transmission network information together with the generation background and the projected load demand. This model was used as the basis of a network assessment to identify the locations in which new generation could be connected, the amount of new generation that could be connected at those locations, and the additional reinforcements that may be required to enable the connection. It should be pointed out that when constructing the transmission network model, typical MVA ratings of transmission circuits were assumed for those circuits that are listed in the future transmission developments and that are proposed in the network reinforcement schemes. Typical transformer ratings were assumed for those new and upgraded super-grid substations based on potential power transfer in the substations.

3.1.1

SHETL Transmission Network

The existing SHETL transmission network comprises an interconnected 275 kV and 132 kV network. The 275 kV network forms the backbone for power transfer from west to east and from north to south. Large generating units are directly connected to the 275 kV network. The 132 kV network is mostly looped into the 275 kV network, providing power diversion support and accommodating power supply to the distribution network. Small generating units, including a number of hydro generating units, are connected to the 132 kV network. As the total power produced from generating units is more than the total power consumed by customers in the SHETL system, power is seen to flow from west to east and from north to south. The 2009 GB SYS suggests that the existing transmission infrastructure has only approximately 450 MW power transfer capability through the North West boundary B1, and approximately 1600 MW power transfer capability through the SHETL-SPT boundary B4. The generation background and projected load demand level for 2020 suggest that a significant amount of power needs to be transferred through these two boundaries due to the high volume of new renewable generation developments in the area. The existing transmission network is not capable of accommodating the required power transfer capacity. As a result, considerable network reinforcements are required.

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A schematic of the anticipated SHETL transmission network in 2020 with new reinforcements is shown in Figure B3.1. The reinforcements include the future transmission network development up to 2015 and the proposed network up-rating and upgrade from 2016 to 2020 and they are as follows:

Rebuilding of the Beauly-Dounreay 275 kV single line to double circuit line with renewable generation at Gordonbush, Strathbrora, Strathy, and Ardross wind farms tee-connected to the 275 kV double circuit line. (Refer to reinforcement (a.) in Figure B3.1).

Up-rating of the Beauly-Blackhillock 275 kV double circuit line. A new 275 kV substation at Knocknagael, which is sited at the tee point of the Beauly-Blackhillock 275 kV double circuit line to Foyers, is constructed to increase network resilience and to facilitate power division to Inverness 132 kV substation. (Refer to reinforcement (b.) in Figure B3.1).

Construction of the Beauly-Denny 400 kV double circuit line and of a 400 kV substation at Beauly, Fort Augustus, and Denny. The 400 kV double circuit line is constructed using the existing 132 kV double circuit route with one 400 kV circuit to be operated at 275 kV and looped into Fort Augustus and Errochty substations by 2020. (Refer to reinforcement (c.) in Figure B3.1).

Upgrade of the east coast 275 kV double circuit line to 400 kV (Refer to reinforcement (d.) in Figure B3.1) which comprises: o

Upgrading of the Blackhillock-Keith-Kintore 275 kV double circuit line via Keith and of the Kintore-Kincardine 275 kV double circuit line via Tealing, to 400 kV operation.

o

Re-conductoring of the other Kintore-Tealing 275 kV double circuit line and of the Tealing-Westfield 275 kV double circuit line via Glenrothes to increase power transmission capacity.

o

Construction of a new 400/275 kV substation at Kintore North which is sited around the crossing point of the Keith-Peterhead 275 kV line and Kintore- Peterhead 275 kV line, and installation of two 400/275 kV transformers at the substation to facilitate connection of the 275 kV lines to Peterhead.

o

Upgrading of the existing Kintore 275/132 kV substation into a 400/275/132 kV substation and installation of two 400/275 kV transformers to facilitate connection of 275 kV network at Kintore.

o

Construction of a new 400/275 kV substation at Tealing West which is sited around the crossing point of the existing Kintore-Kincardine 275 kV line to the Tealing 275 kV substation, and installation of two 400/275 kV transformers at the substation to facilitate connection of 275 kV double circuit line to Tealing.

o

Installation of two new 275 kV cable circuits from Blackhillock to Keith to facilitate connection of the existing two 275/132 kV transformers at Keith. This is required because the existing Blackhillock-Keith 275 kV double circuit line is upgraded into 400 kV.

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a

c

b d

Figure B3.1 – Network Reinforcements in SHETL Transmission System

Construction of the Eastern HVDC link with a power transfer capacity of 1800 MW. The two convertor stations of the HVDC link are sited respectively at Peterhead in the SHETL transmission network and at Hawthorne in the NGET transmission network. Subsea cable circuits are assumed for connection of the two convertor stations.

Construction of the Caithness-Moray coast HVDC link with power transfer capacity of 500 MW to facilitate connection of renewable generation from Orkney Island and of other wind generation in the vicinity of Dounreay. The two convertor substations are assumed to be constructed at Dounreay and Blackhillock and connected via subsea and onshore cable circuits.

It is anticipated that after completion of the network reinforcements, transmission capacity through the North West boundary B1 could reach approximately 6500 MVA for the intact system and 1800 MVA under an N-D outage condition. This onshore transmission capacity is augmented by the 500 MW power transfer capacity of the proposed Caithness-Moray coast HVDC link. It is also anticipated that transmission capacity through the SHETL-SPT boundary B4 could reach approximately 11500 MVA for the intact system and 6400 MVA under N-D outage condition. This onshore transmission capacity is augmented by the 1800 MW power transfer capacity of the proposed Eastern HVDC link. Substations in the SHETL transmission network, such as the existing Beauly 275 kV substation and the 132 kV substations which are close to the west coast and are likely to be upgraded to 400kV or 275 kV, could be considered for potential connection of ISLES offshore renewable generation.

3.1.2

SPT Transmission Network

The existing SPT transmission network comprises 400 kV, 275 kV and 132 kV networks. The 400 kV and 275 kV network forms the backbone for power transfer across the network and for power export to

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the NGET transmission network. Large generating units are directly connected to the 400 kV and 275 kV network. The 132 kV network is connected into the 400 kV or 275 kV substations, accommodating power supplying points to distribution network and connection points for small generation. Because of power transfer from the SHETL transmission network down to the south together with higher generation capacity than demand levels in the SPT system, power will normally flow from north to south in the SPT transmission network and export to the NGET transmission network. The 2009 GB SYS suggests that the existing SPT transmission network has approximately 2000 MW power transfer capability through SPT-NGET boundary B6. The generation background and projected load demand level by 2020 suggest that the combined generation capacity in the SHETL and SPT systems, north of the SPT-NGET boundary B6, is approximately 20 GW, while the maximum demand is only 6 GW. This indicates that a large quantity of power is to be transferred through the B6 boundary down to the NGET transmission network, which creates a significant challenge to the SPT transmission network. In order to accommodate the planned power transfer, deep network reinforcements in the SPT transmission network would be necessary. A schematic of the SPT transmission network with new reinforcements by 2020 is shown in Figure B3.2. The reinforcements include the future transmission network development up to 2015 and the proposed network up-rating and upgrade from 2016 to 2020 and they are as follows:

Upgrade of the east coast 275 kV double circuit line to 400 kV (Refer to reinforcement (a.) in Figure B3.2), which includes: o

Upgrading of the existing Kincardine 275 kV substation into a 400/275 kV substation, and installation of two 400/275 kV transformers to facilitate connection of the 275 kV network at Kincardine.

o

Upgrading of the existing Grangemouth 275/132 kV substation into a 400/132 kV substation with the existing 275/132 kV transformers replaced by 400/132 kV transformers.

o

Construction of a new 400/275 kV substation at Harburn. This substation could be sited in the vicinity the Kincardine/Grangemouth-Currie 275 kV double circuit line and the Strathaven/Wishaw-Smeaton 400/275 kV double circuit line start to run in parallel towards Currie/Smeaton 275 kV substations.

o

Re-conductoring and re-insulating of the Kintore/Tealing-Kincardine 275 kV double circuit line to a 400 kV double circuit line.

o

Re-conductoring and re-insulating of the section of the Kincardine-Currie 275 kV double circuit line to Harburn via Grangemouth to a 400 kV double circuit line.

Upgrade of the east-west 275 kV lines to 400 kV (Refer to reinforcement (b.&c.) in Figure B3.2) including: o

Re-insulating of the Strathaven-Smeaton 275 kV line via Wishaw, Harburn and Kaimes, which is run in parallel with the Strathaven-Smeaton 400 kV circuit on the same towers. This enables the line to be operated at 400 kV, forming a StrathavenSmeaton 400 kV double circuit line and increasing power transfer capability between East and West in the SPT system.

o

Looping of the Strathaven-Smeaton 400 kV double circuit line into the new Harburn 400/275 kV substation to facilitate power transfer from north to either east or west in the SPT system.

o

Upgrading of the existing Wishaw 275 kV substation into a 400/275 kV substation and looping of one Strathaven-Smeaton 400 kV circuit into the Wishaw 400/275 kV substation.

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o

Installation of a second 400 kV cable per phase on both of the Torness-Eccles 400 kV circuits to increase power transfer capability from Torness to Eccles.

a

d b c

Figure B3.2 – Network Reinforcements in SPT Transmission network

Construction of the Western HVDC link with a power transfer capacity of 1800 MW. The two converter substations are assumed to be sited at Hunterston in the SPT transmission network and at Deeside in the NGET transmission network. Subsea cables are assumed for connection of the two convertor stations (Refer to reinforcement (d.) in Figure B3.2).

Installation of series reactive power compensation over a number of 400 kV circuits that are the key to significant power transfer from the SPT transmission network down to the NGET transmission network. It is assumed that around 35% of reactive power compensation degree is applied on following 400 kV circuits: o

Installation of a 1x100 MVAr Series Capacitor on the Strathaven-Coalburn 400 kV circuit at Strathaven side.

o

Installation of a 1x100 MVAr Series Capacitor on the Strathaven-Elvanfoot 400 kV circuit at Strathaven side.

o

Installation of a 1x225 MVAr Series Capacitor on the Gretna-Harker 400 kV circuit at Harker side.

o

Installation of a 1x225 MVAr Series Capacitor on the Moffat-Harker 400 kV circuit at Harker side.

o

Installation of a 1x225 MVAr Series Capacitor on the Eccles-Stella West 1 400 kV circuit at Eccles side.

o

Installation of a 1x225 Mvar Series Capacitor on the Eccles-Stella West 2 400 kV circuit at Eccles side.

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It is anticipated that after completion of these reinforcements in the SPT transmission network, the transmission capacity of the onshore network across the SPT-NGET boundary B6 could reach approximately 9800 MVA for the intact system and 4200 MVA under N-D outage condition. This transmission capacity is augmented by the 3600 MW power transfer capacity over the Eastern and Western HVDC links. Substations in the SPT system, such as the existing Hunterston 400 kV substation and Cruachan 275 kV substation, may be considered for potential connection of ISLES offshore renewable generation.

3.1.3

NGET North & North-East England Transmission Network

The NGET North & North-East England transmission network comprises a 400 kV and 275 kV network. Power transfer through the network is expected to increase over time due to a considerable amount of power export from the SPT system. Two power transfer corridors, which operate in parallel in the NGET North & North-East England transmission network, play an important role for bulk power transfer from north to south through the network. The increasing power transfer from the SPT transmission network to the NGET transmission network not only challenges transmission capability through the SPT-NGET boundary B6, but also challenges transmission capability through the NGET Upper North boundary B7. The 2009 GB SYS suggests that the existing transmission infrastructure has approximately 3500 MW power transfer capability through the NGET Upper North boundary B7. The generation background and projected load demand level by 2020 suggest that generation capacity in the region north of the NGET Upper North boundary B7 is approximately 27 GW, while the maximum demand of the same region is only 9 GW. Considerable power transfer through the boundary is therefore expected. In order to accommodate the planned power transfers, deep network reinforcements are necessary. As well as the proposed Eastern and Western HVDC links, which together could provide 3.6GW of new transmission capacity, the following additional transmission reinforcements are proposed in the NGET North & North-East England transmission network.

Installation of series reactive power compensation over the 400 kV power transfer corridors from the SPT transmission network down to the NGET transmission network. The Harker-Hutton 400 kV double circuit line and the Stella West-Norton 400 kV double circuit line are compensated with around 30%~35% of reactive power compensation degree applied. o

Installation of a 1x100 Mvar Series Capacitor on the Stella West-Spennymoor 400 kV circuit 1 &2 respectively at Stella West side.

o

Installation of a 1x225 Mvar Series Capacitor on the Harker-Hutton 400 kV circuit 1&2 respectively at Harker side.

Up-rating of the existing Hutton-Quernmore 400 kV double circuit line to facilitate the increase of transmission capacity over the line.

Upgrade of the existing Hawthorne Pit-Norton 275 kV line to 400 kV and installation of one more 400/275 kV transformer at Hawthorne Pit-Norton. This upgrade was proposed in this report as the connection of the Eastern HVDC link to Hawthorne Pit-Norton 400/275 kV substation would no doubt require reinforcements of the 400 kV and 275 kV networks at the substation to meet the SQSS criteria.

It is anticipated that after completion of these reinforcements in the NGET Upper North and North transmission network, the transmission capacity of the onshore network through the NGET Upper North boundary B7 could reach approximately 13900 MVA for the intact system and 8800 MVA under

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N-D outage condition. This onshore transmission capacity would be augmented by the 1800 MW power transfer capacity of the Western HVDC link. The Harker 400 kV substation may be considered as a potential connection point for ISLES offshore renewable generation.

3.1.4

NGET North-West England and North Wales Transmission Network

The NGET North-West England and North Wales transmission network is largely made up of 400 kV network with a small number of 275 kV circuits looped with the 400 kV network. The interconnecting circuits to other networks are vital to support north-south power transfers through the network and to accommodate generation export from the network to other networks. The generation background and projected load demand level by 2020 suggest that generation capacity inside the system (Zone 9) is approximately 13 GW, while the maximum demand is only 8.4 GW. This indicates that generation is likely to be exported from this part of the network. The increasing north to south power transfers may challenge transmission capability through the network. New generation connection into the region, including nuclear generation at Wylfa and Round 3 Irish Sea offshore wind developments, will significantly impact on the transmission capability of the network, especially on power transfer corridors associated with the Legacy-Ironbridge 400 kV circuits and Daines-Cellarhead 400 kV circuits. It is anticipated that new reinforcements would be necessary in order to accommodate the increasing power transfers through the network and new generation connection to the network. The following reinforcements have been proposed in the NGET North-West England and North Wales transmission network by 2020.

Construction of the converter station at Deeside 400 kV substation for termination of the Western HVDC link.

Up-rating of the existing Hutton-Quernmore 400 kV double circuit line to increase power transfer capacity over the circuits.

It is understood that other deep network reinforcements are being considered. The timing and scale of these reinforcements is dependent upon the development of the Round 3 Irish Sea offshore wind generation which will connect to 400 kV substations in the network, new nuclear generation connection at Wylfa, and bulk power export to the network via subsea cable circuits from Scotland or from other offshore renewable generation resources, etc. A number of 400 kV substations, such as Penwortham, Deeside, Pentir and Trawsfynydd may be considered to be potential connection points for ISLES offshore renewable generation due to their proximity to the ISLES offshore renewable generation resources and to the transmission network of load centre.

3.1.5

NGET South Wales and Central England Transmission Network

The NGET South Wales and Central England transmission network is made up of 400 kV and 275 kV networks with five 400 kV double circuit lines connecting the network to the rest of the NGET transmission network. There is significant generation located at Pembroke, Oldbury, Seabank, Aberthaw, Barry, Baglan Bay, Fifoots and Didcot power stations. The north- south power transfer has little impact on the NGET South Wales and Central England transmission network due to its location in the NGET transmission network. The generation

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background and projected load demand level by 2020 suggest that generation capacity inside the system (Zone 13) is approximately 12 GW, while the maximum demand is only 5.5 GW. As a result, generation power is likely to be exported from the network to the rest of the NGET transmission network. The internal transmission network in South Wales is sufficient for the existing generation background and demand levels in the area. However, local restrictions may impose constraints on new generation connection into the network. For example, limited power transmission capacity over the 400 kV circuits from Pembroke to Walham via Cilfynydd may constrain bulk generation export from Pembroke to the rest of the system. It has been planned that a new 400 kV substation be constructed at Hirst North, and the existing 400 kV Pembroke to Walham via Cilfynydd double circuit is looped into Swansea North 400 kV substation before connecting to the new Hirst North 400 kV substation before 2015. It is anticipated that after completion of the planned reinforcements, the 400 kV transmission network will have sufficient power transfer capability for the generation export from Pembroke and other power plants in the area. Should more generation be connected to Pembroke substations or to other substations in South Wales, or more power is exported to those substations from, say, a new interconnector, the limited MVA rating of the Cowley-Walham-Minety 400 kV lines may impose a constraint on generation export or power import. Up-rating of the lines may therefore be required. The 400 kV substations close to the south west coast, for example the Pembroke 400 kV substation, may be considered as potential connection points for ISLES offshore renewable generation.

3.1.6

NGET South West Transmission Network

The NGET South West transmission network is made up of a 400 kV network with two 400 kV double circuit lines connecting the network to the rest of the NGET transmission network. The north to south power transfer has no impact on NGET South West transmission network due to its location in the NGET transmission network. The generation background and projected load demand level by 2020 suggest that the generation capacity inside the system (Zone 17) is approximately 3.8 GW, while the maximum demand is only 2.7 GW. As a result, generation and demand in the network is nearly balanced. It is anticipated that new generation could be connected to substations in the area. The MVA ratings of the double circuit lines linking the South West transmission network to the rest of the NGET transmission network would be the key to the amount of new generation seeking connection to the network. Substations in the NGET South West transmission network are generally too far away from the ISLES offshore renewable generation resources to be considered as candidates for ISLES connection points. However, the 400 kV Alverdiscott 400 kV substation might be considered as a potential connection point, should other 400 kV substations closer to the ISLES renewable resources be found to be incapable of accepting the necessary power transfer.

3.1.7

Other Areas of the NGET Transmission Network

Substations in other areas of the NGET transmission network are geographically far away from the ISLES offshore renewable generation resources and would not be considered for connection of the ISLES generation due to uneconomic investment of the offshore transmission network.

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3.1.8


Interconnection of the GB Transmission System

The existing GB system is interconnected with France and Northern Ireland. The cross-channel interconnection with France is a HVDC link with a power export/import capability of circa 2000 MW. The convertor station in the GB system is at Sellindge in Kent. It is understood that the HVDC link usually imports power from France during periods of peak demand. The Moyle interconnector with Northern Ireland is another HVDC link connecting convertor stations at Auchencrosh in the SPT transmission network and Ballycronan More on Islandmagee in Northern Ireland with a power export/import capability of 500 MW. (Due to operational considerations in Northern Ireland, the Moyle interconnector is generally not operated with a transfer above 450MW.) A new HVDC link is being commissioned for interconnection with the Netherlands electricity system. The convertor station in the GB system is at Grain substation. The HVDC link has the capability of up to 1320MW for power export/import between the two systems. A new HVDC link between GB and the Republic of Ireland is scheduled to be commissioned in 2012. It will have a capacity of 500MW, be capable of bi-directional flow, and will be connected at Deeside 400kV substation in the NGET North-West England and North Wales transmission network. Other GB-Ireland HVDC links have been proposed by various organisations, but as yet none are expected to be commissioned in the foreseeable future. One HVDC link with potential capability of 1000MW is being proposed for external interconnection with the Belgium electricity system before 2020, accommodating power exchange capability between the GB and Belgium systems. In addition, a number of further interconnections have been proposed for offshore wind development in the GB system, including the following:

Nord interconnection with a three-terminal HVDC-VSC line linking Norway, Germany and the UK with potential capability of 700MW-1400 MW as a modular development of offshore wind generation.

Norway/UK interconnection with three-terminal HVDC-VSC line linking Norway, Germany and the UK with potential capability of 1000MW-5000 MW as a modular development of offshore wind generation.

Three legged HVDC HVDC-VSC line linking Ireland, Northern Ireland and Wales with potential capability of 1000MW.

Three legged HVDC HVDC-VSC line linking Belium, the UK and the Netherlands with potential capability of 1000MW.

It is anticipated that construction of the interconnections would not only increase power exchange capability across the systems involved, but also provides more opportunities to the development of offshore renewable generation, for example the development of ISLES offshore renewable generation.

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3.2


REPUBLIC OF IRELAND TRANSMISSION SYSTEM

Information on the Irish transmission network was extracted from the Transmission Forecast Statement and on Grid 25 proposals, both published by EirGrid,

3.2.1

Existing Ireland Transmission Network

The transmission network in the Republic of Ireland comprises a 400 kV, 220 kV and 110 kV network. The 400 kV and 220 kV network forms the backbone of the grid. While the 400 kV network provides a high transmission capacity link between Galway on the west coast and Dublin on the east, the 220 kV network, comprising a number of single circuit loops, transmits power to the key 220 kV substations around the country. All large generation stations are connected to the 400 kV or 220 kV network. The 110 kV network reaches every county in Ireland and many 110 kV lines run in parallel paths to the 220 kV lines, providing power diversion support for certain conditions or in the event of an unexpected circuit outage.

Figure B3.3 – Network Performance in Ireland Transmission System in 2010

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It is anticipated that the existing transmission infrastructure is capable of accommodating power transmission to the 400 kV, 220 kV and 110 kV substations and catering for power supply to customers for most operational scenarios, in which various generation dispatches could be used to meet the system demand requirements with system performance being compliant with planning standards. For some operational scenarios, however, a number of transmission lines and substations, as highlighted in Figure B3.3, may have overload issues under various contingency conditions for specific generation dispatches.

3.2.2

Planned Ireland Transmission Network by 2016

EirGrid’s “Transmission Forecast Statement for the period of 2010-2016” network developments expected to be progressed in the 2010-2016 period. mainly focus on transmission network expansions and reinforcements which demand growth and new onshore generation and demand connections. The of the major 400 kV and 220 kV network developments anticipated by 2016.

provides details of the The development plans are required to facilitate following is an overview

Lodgewood 220 kV development, in which a new Lodgewood 220/110 kV substation will be constructed and connected into the existing Arklow-Great Island 220 kV line, and the Crane 110 kV substation is looped to the new Lodgewood 220/110 kV substation by 2010. This reinforcement ensures adequate infrastructure to be in place to accommodate the growth of demand in the area and increases power supply reliability at Crane.

New Aghada-Raffeen 220 kV circuit and Glanagow-Raffeen 220 kV circuit. Installation of the new Aghaha-Raffeen 220 kV circuit in 2010 and the new Glanagow-Raffeen 220 kV circuit by 2011 enables direct generation export from the existing Aghada power station and from the new Glanagow power station, which is tail connected to Aghada power station, to Raffeen 220 kV substation, increasing power transmission capability to Raffeen and reducing transmission losses over 220 kV transmission network.

Srananagh 220 kV development, in which the existing Srananagh 110 kV substation is expanded into a 220/110 kV substation and a new 220 kV circuit is installed from Flagford to Srananagh by 2011. This reinforcement enables 220 kV network extended into the North West and increases power supply reliability to Srananagh.

New 400 kV line between the Republic of Ireland and Northern Ireland. This new 400 kV line will connect the Woodland 400/220 kV substation near Dublin and the new 400/275 kV substation at Turleenan in Northern Ireland. This 400 kV line will significantly increase the cross-border power exchange capability and will facilitate efficient operation of the All-island electricity market. It is also a key enabler for onshore renewable generation connections in the north-west of the island of Ireland.

The East-West interconnector between Ireland and GB. This 500 MW interconnector, scheduled to be in place in 2012, will connect the Woodland 400/220 kV substation in the Ireland system and the Deeside 400 kV substation in the GB system.

Finnstown 220 kV development. A new Finnstown 220/110 kV substation will be constructed and looped into the existing Inchicore-Maynooth 220 kV lines, increasing power supply capability and reliability in the West Dublin area. The development is scheduled to be completed by 2013.

Balgriffin 220 kV development. A new Balgriffin 220/110 kV substation will be constructed and connected to Finglas 220/110 kV substation, increasing power supply capability and reliability in the North East Dublin area. The development is scheduled to be completed by 2013.

Kilpaddoge 220 kV development. A new Kilpaddoge 220/110 kV substation will be constructed and looped into the existing Clashavoon-Tarbert and Killonan-Tarbert 220 kV lines. In addition, a new submarine cable circuit will be installed to connect the new Kilpaddoge 220/110 kV substation to Moneypoint 400/220/110 kV substation. The development enables a new hub for

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power flows into the south-west area and creates a new power transfer path for generation power export to the south-west area from Dublin-Moneypoint group of generators. The development is scheduled to be completed by 2013.

Ballyvouskill, Kishkeam and Knockanure 220 kV development. Three new 220/110 kV substations will be constructed at Ballyvouskill, Kishkeam and Knockanure respectively and looped into the existing Clashavoon-Tarbert 220 kV line. The development is needed to accommodate the planned generation in the south-west area and is scheduled to be completed by 2014.

400 kV substation at Laois. A 400/110 kV substation will be constructed at Laois and looped into the existing Moneypoint-Dunstown 400 kV line to provide necessary voltage support of the 110 kV network surrounding Laois. Construction of the substation is scheduled to be completed by 2014.

In addition, up to 15 new 110 kV substations are planned for construction before 2016, connecting the distribution system or directly-connected customers to the grid. It is anticipated that after completion of the developments, the transmission network would be capable of accommodating power transmission to all substations and catering for demand growth across the system for most operational scenarios. Some areas of the network as highlighted in Figure B3.4 below, however, may still experience overloads under various contingency conditions. Figure B3.4 indicates that for the given generation background and load demand levels by 2016, the highlighted transmission circuits would have no extra capacity for new generation connection at the following substations and areas without further reinforcements.

220/110 kV substations at Arklow, Castledockrill, and Great Island in the south-east coast area.

220/110 kV substations at Knockraha and Clashavoon in the southern area.

220/110 kV substations at Castlebar and Cashla in the west coast area.

110 kV substations at Letterkenny, Cathaleen’s Fall, Srananagh, Flagford and Arva in the northwest area.

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Figure B3.4 – Network Performance in Ireland Transmission System by 2016

3.2.3

Grid 25 Transmission Network

In 2009 EirGrid published its “Grid Development Strategy - Grid 25”, with the initiative to put in place safe, secure, and affordable electricity supply throughout Ireland, supporting economic growth and providing a roadmap for renewable and sustainable energy by 2025. The strategy, which was based on the findings of the All-Island Grid Study, demonstrates the feasibility of at least 40% renewable electricity in the Ireland and Northern Ireland system by 2020. EirGrid stated that to facilitate the necessary increase in renewable generation and to adequately meet the demands of the electricity customer, the capacity of the bulk system will need to be doubled by 2025. This will be achieved through major reinforcements to the existing transmission network using the best technological solutions available. The following is an overview of the major network developments in Grid 25 for all regions shown in Figure B3.5 below.

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Figure B3.5 – Seven Regions in Ireland Transmission System North West Region The transmission network in the North West is predominately at 110 kV with little 220 kV and no 400 kV network. Flagford 220 kV substation is the only 220 kV substation in the region with two 220 kV circuits linking the substation to other 220 kV substations in the rest of the island. This region is particularly rich in renewable resources for wind and wave generation. It is expected that the region will have up to 60% of demand growth, up to 691 MW, 880 MW, and 269 MW of wind generation in Donegal, Mayo/Galway and Leitrim/Roscommon areas respectively, and up to 240 MW of wave generation and 31 MW of offshore wind generation in Mayo/Galway area by 2025. Network developments of the region in Grid 25 mainly consist of upgrading of approximately 700 km of existing transmission network and installation of new circuits with key developments as follows:

Extension of the 220 kV network into Sligo to increase transmission capacity from Sligo and Srananagh to the backbone 220 kV network and to facilitate future potential extension of the 220 kV network further up to Cathleen’s Fall and Letterkenny.

110 kV reinforcements between Killybegs (Binbane substation) and Letterkenny and between Ballaghadreen (Tonroe station) and Castlebar to increase transmission capacity for new wind generation connection and demand growth in the areas.

Major infrastructural development from Mayo to the main bulk system in the eastern part of the region. The 220 kV transmission network will be extended to Bellacorick and a new 220/110 kV substation built at Bellacorick.

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Further integration of the Donegal and NI transmission networks. Potential extension of 275/220 kV network to Donegal area and installation of new 275/110 kV lines to the NI system could be required for connection of renewable generation in Donegal area and in the NI system.

It is anticipated that implementation of the reinforcements would enable the network of the region to accommodate power supply to the forecast demand levels and to connect the given renewable generation capacity. However, if ISLES offshore wind generation development of the north coast is to seek connection at a substation in the region, for example a 300 MW offshore wind connection at Letterkenny or at Coolkeeragh, the proposed reinforcement in Grid25 would not be sufficient and additional reinforcements both at the substation and in the deep network are certainly required. North East Region The transmission network in the North East region consists of 400 kV, 220 kV and 110 kV circuits. The existing 220 kV network and the progressing 400 kV North-South interconnector between the Ireland and the NI systems via Mid-Cavan in the region provides a strong power transfer corridor between Dublin and Belfast. This region has some potential for onshore and high potential for offshore wind generation development. The Cavan 400/220 kV, Louth 275/220 kV and Gorman 220/110 kV substations provide potential locations for connection of the new generation, especially for offshore wind generation off the east coast of Ireland. It is expected that the region will have up to 60% demand growth, and up to 145 MW and 125 MW onshore and offshore wind generation by 2025. Network development of the region in Grid 25 mainly consists of:

Installation of the North-South Interconnector (400 kV) connecting Woodland to Turleenan via Mid-Cavan to increase power exchange capability between the Ireland and NI systems and to facilitate efficient operation of the All-Island electricity market.

Strengthening of power circuits between the North West region and the North East region to facilitate large power flows, especially the power flows for renewable generation export from North West region to the 400 kV and 220 kV networks in the North East region.

Reinforcement of 110 kV networks supplying Cavan and Monaghan to accommodate demand growth in the areas, and upgrading about 240 km of the existing transmission network to increase transmission capacity.

It is anticipated that implementation of the reinforcements would enable the network of the region to accommodate power supply to the forecast demand levels and to connect the given renewable generation capacity. However, if ISLES offshore wind generation development off the east coast of Ireland is to seek connection at a substation in the region, for example a 300 MW offshore wind connection at Louth, the proposed reinforcement in Grid25 would not be sufficient and additional reinforcements both at the substation and in deep network may still be required. West Region There are 400 kV, 220 kV and a number of 110 kV circuits in the region to facilitate generation export from large-scale power stations in Tarbert, Moneypoint and Tynagh to the rest of the island and accommodate power supply to distribution network. The region features an availability of renewable resources for wind and wave generation. It is expected that the region will have up to 60% of demand growth and up to 440 MW of wind generation and 75 MW of wave generation by 2025. Network development of the region in Grid 25 mainly consists of:

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Upgraded networks supplying the large urban centres of Ennis and Limerick to enhance power supply reliability of the network.

Up-rating over 250 km of existing networks to facilitate higher transmission capacity, using existing corridors where possible.

Strengthening the transmission capacity across the Shannon Estuary to facilitate efficient power transfer from Moneypoint to Tarbert and other substations in the southwest region.

It is anticipated that implementation of the reinforcements would enable the network of the region to accommodate power supply to the forecast demand levels and to connect the given renewable generation capacity. As substations in this region are unlikely to be considered for connection of the proposed ISLES offshore generation, additional reinforcements in this region may not be necessary. East Region There are large-scale thermal generating stations at Poolbeg, North Wall, Huntstown and Irishtown and a pumped-storage station at Turlough Hill in the region. In addition, there is a potential for high levels of conventional generation and offshore wind generation in the region as well. It is expected that the region will have up to 80% of demand growth, 30% of demand in the island, and up to 240 MW of wind generation by 2025. Woodland 400/220 kV, Carrickmines 220/110 kV and Arklow 220/110 kV substations could be potentially taken as locations for connection of offshore wind generation development off the east coast. The 220 kV network within Dublin and the 220 kV and 400 kV networks linking the region to the rest of the island will require significant development to facilitate significant amount of power flows to and from the region and to accommodate future imports and exports through the planned East-West interconnector to the GB system. Network developments of the region in Grid 25 mainly consist of upgrading of approximately 450 km of existing 220 kV and 110 kV transmission network and installation of new circuits with key developments as follows:

Strengthening of network into and out of the region to allow the demand to be met by renewable generations located mainly in the west of the country.

Strengthening of network serving Dublin City load and reinforcement of the network to cater for demand growth in Kildare and North Wicklow.

Development of the local networks to allow north south power flows to by-pass the network serving the Dublin load;

Construction and connection of new 220 kV stations in North and West Dublin to cater for the rapidly growing developments in these areas;

It is anticipated that implementation of the reinforcements would enable the network of the region to accommodate power supply to the forecast demand levels and to connect the given renewable generation capacity. However, if ISLES offshore wind generation development off the east coast is to seek connection at a substation in the region, for example a 300 MW offshore wind connection at Arklow, the proposed reinforcement in Grid 25 would not be sufficient and additional reinforcements both at the substation and in deep network would be required.

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Midlands Region Power supply in the region is mainly achieved through the meshed 110 kV network. A number of 400 kV and 220 kV circuits pass through the region, potentially providing locations where new generation in the region can be connected and voltage of the 110 kV network can be effectively supported for power supply to distribution networks. It is expected that the region will have up to 40% of demand growth and up to 160 MW of wind generation by 2025. Network developments of the region in Grid 25 mainly consist of upgrading of approximately 225 km of existing transmission network and installation of new circuits with key developments as follows:

Construction of a 400/110 kV substation at Laois and connection of the 400/110 kV substation to the existing 400 kV line to strengthen the 110 kV network around Portlaoise, providing transmission capacity to supply the continuing growth of demands in Kildare and Laois.

Reinforcement of the local network to cater for continued demand growth in the gateway towns of Athlone, Mullingar and Tullamore.

Upgrading of the network to facilitate power export from both renewable and conventional sources and maximise the use of existing power corridors.

It is anticipated that implementation of above reinforcements enables the network to have the capability to accommodate power supply to the forecast demand levels and connection of the future renewable generation. As substations in this region are unlikely to be considered for connection of the proposed ISLES offshore generation, additional reinforcements in this region may not be necessary. Southeast Region Power transmission and power supply in the region is achieved through the 220 kV and 110 kV networks. Three 220 kV circuits linking the region to the rest of the island are the main paths of power transfer. In addition, a number of 110 kV circuits, which mostly run in parallel to the 220 kV circuits, provide power transfer support to the 220 kV circuits. There are existing large-scale generation facilities at Great Island station in the region. Additionally, this region has good wind resources. It is expected that the region will have up to 45% of demand growth and up to 545 MW of onshore and 445 MW of offshore wind generation by 2025. Lodgewood, Waterford and Great Island 220/110 kV substations could be potential locations for connection of offshore wind generation development off the south east coast. Network developments of the region in Grid 25 mainly consist of upgrading of approximately 490 km of existing 220 kV and 110 kV transmission network and installation of new circuits with key developments as follows:

Strengthening of the 220 kV links to both Dublin and Cork to facilitate increased power flows. This could be achieved by either upgrading the existing 110 kV circuits into 220 kV or installing a double 220 kV circuit on the existing 220 kV transmission routes.

Strengthening of the networks supplying the major cities and towns in the region to accommodate demand growth.

Up-rating of the 220 kV and 110 kV circuits to maximize the use of existing corridors where possible to facilitate increase of transmission capacity of the circuits.

A new interconnector from this region to either GB system or mainland Europe system will enable the export and import of power when appropriate.

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It is anticipated that implementation of the reinforcements would enable the network of the region to accommodate power supply to the forecast demand levels and to connect the given renewable generation capacity. However, if ISLES offshore wind generation development off the south east coast is to seek connection at a substation in the region, for example a 300 MW offshore wind connection at Lodgewood, the proposed reinforcement in Grid 25 would not be sufficient and additional reinforcements both at the substation and in deep network would be required. Southwest Region The transmission network in the region consists of both 220 kV and 110 kV circuits. Three 220 kV circuits linking the region to the rest of the island are the main paths of power transfer. In addition, a number of 110 kV circuits, which mostly run in parallel to the 220 kV circuits, provide power transfer support to the 220 kV circuits. There are thermal generation facilities at Marina and Aghada with plans for new generators at Aghada and nearby Whitegate. The region has plenty of natural renewable resources for wind and wave generation development. Knockanure and Clashavoon 220/110 kV substations and Tralee and Clonkeen 110 kV substations along the southwest coast could be potentially taken as locations for connection of offshore wind and wave generation. It is expected that the region will have up to 60% of demand growth and up to 1610 MW of wind generation and 185 MW of wave generation by 2025. Network developments of the region in Grid 25 mainly consist of upgrading of approximately 130 km of existing 220 kV and 110 kV transmission network and installation of new circuits with key developments as follows:

Strengthening of the Cork network to allow power to be exported from the two large gas-fired generators in East Cork to the rest of the island.

Planned grid reinforcements to connect significant amounts of wind generation.

Significant strengthening of transmission capacity between the Southwest and the Southeast to allow excess power to flow from both renewable and conventional sources to supply demand in other parts of the country.

It is anticipated that implementation of the reinforcements would enable the network of the region to accommodate power supply to the forecast demand levels and to connect the given renewable generation capacity. As substations in this region are unlikely to be considered for connection of the proposed ISLES offshore generation, additional reinforcements in this region may not be necessary.

3.2.4

Interconnections

The Irish system is currently connected to the NI system and will soon be interconnected to the GB system. It is anticipated that additional interconnectors could be constructed to further link the Ireland system to the GB system, and even possibly to the mainland Europe system. Interconnection with the GB/Europe System The existing transmission network in the Ireland is not directly connected to the GB or the mainland Europe system. However, the planned 500 MW East-West interconnector will be in place in 2012. It is likely that before 2025 at least one further interconnector from the Ireland system to another system, either Britain or France, will be in place. Greater penetration of renewable generation may provide a case for still further interconnection projects. Grid 25 will provide for the connection of further interconnectors along the south-east or south coast as these are the most likely regions for

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interconnectors to connect the system. These interconnectors could play a significant role in internationalising the Irish energy market and in facilitating the anticipated high levels of renewable generation on the island by providing a means to export excess generation when output from renewable generation is high and to import power when it is low.

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3.3


NORTHERN IRELAND TRANSMISSION SYSTEM

Information on the transmission network was extracted from the SONI Transmission Seven Year Statement and Seven Year Generation Capacity Statement.

3.3.1

Existing and Planned Transmission Network

The existing transmission network in Northern Ireland (NI) consists of 275 kV and 110 kV networks. The 275 kV network, comprising double 275 kV circuits and multiple 275 kV loops, forms the backbone of the system and covers most power supply areas. All large generation stations at Coolkeeragh, Ballylumford and Kilroot are connected to the 275 kV network. The 110 kV network reaches to every county in NI, providing power supply points to the distribution network and directly connected customers and catering for connection of renewable generation of the area. Many 110 kV lines run in parallel with 275 kV lines providing power diversion support for certain conditions or in the event of an unexpected circuit outage. The NI system is connected to the Republic of Ireland via the Tandragee/Louth 275/220kV double circuit and two power flow controlled 110kV lines. Each 275 kV circuit has a designed power transmission capacity of 600 MVA, but the total transfer capacity between the two systems is generally restricted to approximately 300MW due to system security considerations. The two 110 kV lines provide support to either system for certain conditions or in the event of an unexpected circuit outage between the two systems. The NI system is also connected to the GB system via the Moyle interconnector, which was constructed as a dual monopole HVDC Link with two coaxial undersea cables from Ballycronan More, to Auchencrosh, Ayrshire, Scotland. The link has a physical installed capacity of 500MW, but is currently operated at maximum of 450 MW power exchange. The converter station at Ballycronan More is connected to the 275kV network. A new 400 kV line, originally scheduled to be completed by 2012, will connect the Woodland 400/220 kV substation near Dublin and a new 400/275 kV substation at Turleenan in Northern Ireland. Installation of the new line will enable a significant increase in power exchange capability between the Ireland and Northern Ireland and will facilitate efficient operation of the All-Island electricity market. The expected completion date for this new line is currently uncertain. Studies of the NI transmission network show that the areas of Islandmagee in the east of the province and Coolkeeragh in the northwest cannot accommodate major new generation connections without significant onshore system reinforcement or expansion. In other areas there is some scope for generation connection without major system development. However, as the flows on the network increase due to load growth and transit flows from Great Britain to Northern Ireland and Republic of Ireland via the interconnectors, there will be a requirement to support the voltage during certain circuit outage conditions.

3.3.2

2020 Transmission Network

The All-Island Grid Study suggests that the planned NI transmission network has insufficient transmission capability to cater for new generation seeking connection to the network, particularly for renewable generation along the North Coast and in the Omagh and Strabane areas by 2020. For the expected generation portfolios, in which up to 8000 MW wind generation is connected to the All-Island system by 2020, it is anticipated that following transmission circuits would be overloaded in the intact network or under outage conditions without reinforcements:

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Coolkeeragh-Magherafelt 275 kV lines

Coolkeeragh-Strabane 110 kV lines

Coleraine-Kells 110 kV lines

Omagh-Dungannon 110 kV lines

Letterkenny-Strabane 110 kV line

In order to secure connection of the projected new generation capacity in both Northern Ireland and Donegal region, the All-Island Grid Study suggests that the 275 kV network needs to be extended to Omagh, Strabane and even Letterkenny, where a significant amount of wind generation is likely to be connected. With more new generation seeking connection in NI and Donegal, studies are currently being undertaken by the system owners and operators to determine the reinforcements that will be proposed.

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B4. 4.1


ASSESSMENT OF TRANSMISSION CAPABILITY IN GB IN 2020 INTRODUCTION

The connection of ISLES offshore renewable generation into the onshore transmission systems is not a trivial problem. For the purpose of developing credible ISLES concepts, the initial requirement is to understand the transmission capability of the network for the timeframe of circa 2020. This is necessary to establish the network environment into which ISLES offshore renewable generation must connect to. The GB transmission network capacity has been assessed in the most robust fashion possible based on publically available network information. A detailed model of the full GB system was developed to determine the magnitude and sensitivity of the available network capacity, and the impact of different generation levels on network flows. The GB onshore system comprises the primary load centre for connection of the ISLES offshore renewable generation. The following strategic areas were selected across the onshore system due to their proximity to the western coast and relative strength of the transmission network for new generation connection: Northern Scotland, Mid-Scotland, Northern England / North Wales and South Wales / Southern England. In view of the level of capacity which is likely to be required, the minimum network voltage level for connection was selected at 400kV. The selected 400 kV substations include:

SHETL transmission network o

Beauly 400/275 kV.

SPT transmission network o

Inverkip 400 kV

o

Hunterston 400 kV.

NGET transmission network o

Harker 400 kV

o

Heysham 400 kV

o

Penwortham 400/275 kV

o

Deeside 400 kV

o

Pentir 400 kV

o

Trawsfynydd 400 kV

o

Pembroke 400 kV

o

Alverdiscott 400 kV

The methodology applied in assessment of generation connection capability in the GB onshore system is as follows:

For each selected substation, an initial power flow base case was built to meet the winter peak demand. A deterministic method together with the scaling technique detailed in Appendix C of the NET SQSS was applied to determine MW output of the power station generation. All wind generation is assumed to have a 72% availability factor and other conventional generation a 100% availability factor at winter peak.

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Generation at or near to the selected substation is operated at 100% of the available MW capacity. Generation located in the same study zone as the selected substation is operated at 70%~80% of the available MW capacity, while generation outside of the study zone is operated at the scaled MW output level.

Should power transfer through the upper boundary affect generation connection capability of the selected substation, upper boundary power transfer was fixed to the maximum forecast capability. This is particularly important for the northern boundaries to remove the sensitivity of the findings to the level of generation connected to the north of the proposed connection points. This approach also means that any additional transmission reinforcement dependencies for that generation are not included in the capacity assessment. The planned maximum boundary flows were taken from the 2009 SYS forecasts for 2009- 2015 in GB SYS and then extrapolated linearly to estimate the 2020 boundary flows.

The level of generation that can be connected to the key substation is then determined to be the level that just meets the NET SQSS criteria. This assessment is based on a secure load flow which includes consideration of single circuit outage (N-1), single double-circuit outage (N-D), and a single circuit outage with the prior outage of another circuit in the key substation (N-1-1). Winter rating of transmission circuits and transformers was used to check whether they are within the acceptable loading level subsequent to the considered outage conditions.

In addition to new generation connection capability at the selected substations, transmission capability across following system boundaries was also assessed. The purpose of the assessment is to identify the maximum generation power that is capable of being transferred through the boundaries without breaching the NET SQSS criteria. The following boundary flows were considered:

North-West Boundary B1 in the SHETL system

SHETL-SPT Boundary B4 between SHETL and SPT systems

SPT-NGET Boundary B6 between SPT and NGET transmission networks

Upper North Boundary 7 in the NGET transmission network

For each boundary, the maximum power flow over transmission lines, transformers and HVDC links across the boundary, which just meets the NET SQSS criteria, is regarded as the steady state transmission capability of the boundary. Given the total load demand levels in the region, the amount of generation output from all generating units of the region is regarded as effective generation in the region. Please note that the generation connection capacities identified within an individual zone, i.e. within the same boundary, are mutually exclusive and cannot both be used. Therefore, the calculated connection capacities of two nearby nodes cannot simply be summed, as the presence of a power injection at one of the nodes will reduce the available capacity at the other. Please also note that the 2009 SYS does not include any Round 3 Offshore Wind Developments or any Scottish Offshore Wind Exclusivity Agreements approved by the Crown Estate except for Beatrice of 920 MW. The Round 3 and the STW sites have ramifications on the network capacity in the vicinity of the selected connection substations, in particular for the network on the East Coast. However, for the purposes of assessing the network capacity for connection of the ISLES offshore renewable generation, it is only essential to consider the generation projects that affect the west-coast connection capacity, or dominate north south power flows.

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4.2


SHETL TRANSMISSION NETWORK

The best potential point for connection of the ISLES offshore renewable generation in the SHETL transmission network in Northern Scotland is Beauly 400 kV substation, as shown in Figure B4.1.

Figure B4.1 – SHETL Transmission network

4.2.1

Beauly 400 kV Substation

Because of its location, Beauly 400 kV substation plays an important role for the north to south and west to east power transfer in the SHETL transmission network. In addition to 15 MW hydro generation at Torr Achilty, about 450 MW of onshore wind generation is expected to be directly or indirectly connected to Beauly by 2020. The Beauly-Denny 400/275 kV double circuit line and the Beauly-Blackhillock 275 kV double circuit line constitute the key north to south and west to east power transfer corridors by 2020. The BeaulyInverness-Elgin-Keith 110 kV line and the Beauly-Boat of Garten-Keith 110 kV line, which are run in parallel with the Beauly-Blackhillock 275 kV double circuit line and form the 275 kV and 110 kV loops, support the west to east power transfer and provide power diversion under outage conditions. The new generation connection capacity at the substation is affected by several factors including:

Transmission capability of the 275 kV and 110 kV loops taking into account outage conditions of the Beauly-Denny 400/275 kV double circuit line.

New generation developments in the vicinity of Dounreay 275 kV substation and in the areas along the Dounreay-Beauly 275 kV and 132 kV lines.

New generation connection at Dounreay or higher generation export to Thurso from Orkney.

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The initial load flow assessment suggests that practically no generation could be connected to Beauly without the proposed HVDC link between Caithness and Moray. Limited transmission capacity over the 275 kV & 132 kV loops imposes constraints on the generation connection capacity at Beauly. With the proposed HVDC link, which is assumed to export 500 MW power from Dounreay to Blackhillock, however, approximately 650MW-700MW of generation could be connected to Beauly. It should be pointed out that if other new renewable generation is connected to Dounreay or to other substations along the Dounreay-Beauly 275 kV double circuit line, the resultant generation connection capacity at Beauly will reduce accordingly. Increasing the generation connection capacity at Beauly would require upgrading of the BeaulyBlackhillock 275 kV double circuit line to 400 kV, and may require further increase of transmission capacity from Blackhillock to Kintore, subsequent to connection of Round 3 offshore wind generation in Scottish waters and of Shetland Island wind developments either to Keith or to Blackhillock. This takes into account the reinforcements proposed as part of the ENSG work and referenced in the National Planning Framework 2. Although several offshore resources in the ISLES zone are in relatively close proximity to Beauly, the limited new generation connection capability of the substation and the extensive reinforcements required to increase the transmission capacity in this area would indicate that Beauly is not a preferred location for connection of the ISLES offshore renewable generation.

4.2.2

SHETL North West Boundary (B1)

By 2020 the North-West boundary B1 in the SHETL transmission network consists of the Beauly– Denny 400/275 kV double circuit line, the Beauly-Blackhillock 275 kV double circuit line, the two 275/132 kV transformers at Keith, and the HVDC link between Caithness and Moray. The total transmission capacity over the transmission circuits and transformers and over the HVDC link across the boundary B1 is shown in the table below. The resultant SQSS capability of the boundary was derived by assuming that the Beauly–Denny 400/275 kV double circuit line is in outage condition. Table B4.1 – MVA Capacity across Boundary B1

AC Transmission

Summer

Winter

Total Capacity MVA

5770

6560

SQSS Capability MVA

1580

1870

500

500

Caithness-Moray HVDC Link

An initial load flow assessment suggests that the N-D secure transmission capability across the NorthWest system boundary B1 is around 1.78 GW including power transfer over the Caithness-Moray HVDC link. Given the maximum load demand level of 0.54 GW and generation capacity of 4.18 GW in the region which is north of the North West boundary B1 by 2020, it is anticipated that approximately 2.36 GW could be exported from units in the region without breaching the NET SQSS criteria. Limited transmission capacity over the 275 kV & 132 kV loops constrains the network’s ability to accept more generation from units located in the region. It should be noted that in order to achieve the resultant boundary power transfer capability, power flows over the Caithness-Moray HVDC link and over the 132kV/132kV phase shifter transformers at Beauly would need to be closely coordinated.

4.2.3

SHETL-SPT Boundary (B4)

By 2020 the SHETL-SPT boundary B4 between the SHETL and SPT transmission networks consists of the Beauly–Denny 400/275 kV double circuit line, the Kintore-Kincardine 400 kV double circuit line, the Tealing-Westfield/Glenrothes 275 kV double circuit line, the Dalmally/Inverarnan-Windyhill 275 kV

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double circuit line, the Sloy-Windyhill/Helensburgh 132 kV double circuit line, the SloyWindyhill/Strathleven 132 kV double circuit line, and the Eastern HVDC link between Peterhead and Hawthorn Pit. The total transmission capacity over the HVAC transmission lines and over the Eastern HVDC link is shown in the table below. The resultant SQSS capability of the boundary was derived by assuming that the Beauly–Denny 400/275 kV double circuit line is in outage condition. Table B4.2 – MVA Capacity across Boundary B4

AC Transmission

Summer

Winter

Total Capacity MVA

10074

11678

SQSS Capability MVA

5884

6988

1800

1800

Eastern HVDC Link

An initial load flow assessment suggests that transmission capability across the SHETL-SPT boundary B4 is around 4.94 GW including 1.80 GW power export over the Eastern HVDC link. This was achieved under the assumption that power transfer through the North West Boundary B1 reaches its maximum level of 1.78 GW. Given the maximum load demand level of 1.78 GW and generation capacity of 9.38 GW in the region which is to the north of the SHETL-SPT boundary B4, it is anticipated that approximately 6.87 GW could be exported from units in the region without breaching the NET SQSS criteria. Limited transmission capacity over the Kintore-Tealing 275 kV double circuit line constrains the network’s ability to accept more generation from units located in the region. An increase of power transfer capability across the SHETL-SPT boundary B4 would require further reinforcements in the SHETL transmission network including up-rating or upgrade of the KintoreTealing 275 kV double circuit line and construction of new power transfer corridors down to the SPT system. Additionally, deep reinforcements along the north south power transfer corridors from Scotland to England and Wales may be required as well.

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4.3


SPT TRANSMISSION NETWORK

Two 400 kV substations, Inverkip and Hunterston on the west coast of Scotland in the SPT transmission network, shown in Figure B4.2, were selected as potential connection points for ISLES offshore renewable generation due to their proximity to the ISLES offshore renewable resources.

Cruachan SHETL-SPT Boundary B4

Inverkip

Hunterston SPT-NGET Boundary B6

Figure B4.2 – SPT Transmission network

Please note that power transfer levels through the SHETL-SPT boundary B4 will impact generation connection capability at the two substations. It is assumed that the maximum transfer across boundary B4 would reach 4.3 GW respectively by 2020 including the power transfer via the Eastern HVDC link. This assumption was made based on the available information of generation and load demand levels in the SHETL transmission network for 2009/10-2015/16 published in the GB SYS.

4.3.1

Inverkip 400 kV Substation

There are four 400 kV transmission circuits connecting Inverkip 400 kV substation, and no generation is expected to be connected to the substation by 2020. The initial load flow assessment suggests that around 1850 MW-2050 MW of generation could be connected to Inverkip without breaching the NET SQSS criteria. The lower generation connection capability was derived based on the condition that all units in the SPT transmission network are operated at 80% of the available capacity with the maximum power transfer of 4.3 GW through the SHETL-SPT boundary B4, while the higher generation connection capability was derived based on the condition that all units in the SPT transmission network are operated at 70% of the available capacity with the average power transfer of 3.0 GW through the SHETL-SPT boundary B4. Overloading on the Inverkip-Strathaven 400 kV line under N-D outage condition constrains the network’s ability to accept more generation at Inverkip.

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4.3.2


Hunterston 400 kV Substation

There are four 400 kV transmission circuits connecting Hunterston. The 400 kV transmission network at Hunterston mainly facilitates generation export from Hunterston nuclear power plant, power transfer among 400 kV substations within the SPT system, and power transfer to Deeside via the Western HVDC link. Nuclear generation of 1089 MW is connected to Hunterston by 2020. Additionally, the Western HVDC link exports 1800 MW power from Hunterston to Deeside. The initial load flow assessment suggests that around 2000 MW-3000 MW of new generation could be connected to Hunterston without breaching the NET SQSS criteria. Variation of the new generation connection capacity is dependent upon generation output levels from units in the SPT transmission network and power transfer levels through the SHETL-SPT boundary B4. Should more generation be connected to Hunterston, the Elvanfoot-Moffat 400 kV line may experience an overload under N-D outage conditions. A number of factors will affect the available generation connection capacity at Hunterston:

Power transfer levels through the SHETL-SPT boundary B4.

Other new generation which is not included in the 2020 generation background and may be connected to the SPT transmission network around 2020, such as Round 3 offshore wind development in Scottish waters and the east coast SEZ before 2020.

Wind generation output levels considered in the SPT system.

Decommissioning of the existing nuclear generation or large coal generation in the SPT system, such as decommissioning of Longannet plant with a total network entry capacity of 2304 MW.

The load flow sensitivity analysis suggests that:

A moderate to full uptake of the East Coast SEZ and Round 3 projects has the potential to drive the available connection capacity to zero.

Connection of new generation including 500 MW of Round 3 offshore wind, and 500 MW Biopower CHP in the SPT network before 2020 will cause a decrease of new generation connection capacity at Hunterston by 150 MW-300 MW, resulting in a total new connection capacity range of around 1700 MW-2550 MW.

Connection of 500 MW offshore wind development at Moray Firth has insignificant impact on new generation connection capability at Hunterston provided that power flows from the SHETL transmission network down to the SPT transmission network is within the maximum power transfer forecast.

Decommissioning of the Longannet plant will result in an increase of generation connection capacity at Hunterston of between 800MW and 1400 MW. This is because decommissioning of the plant reduces power flow across the 400 kV network in the SPT system, giving extra transmission capability for new generation connection at Hunterston.

Decommissioning of the Hunterston nuclear unit without considering installation of new nuclear units at the substation before 2020 will result in an increase of generation connection capacity to approximately 3000 MW-4000 MW.

Consideration of these of the factors indicates that 2-3GW of connection capacity could be available in the region of Hunterston without the requirement for any extensive deep onshore reinforcement. The available generation connection capacity could even increase to 3.4-4.1GW following decommissioning of the Longannet large coal power plant.

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Hunterston can therefore be considered to be an attractive location for connection of ISLES offshore renewable generation,

4.3.3

SPT-NGET Boundary (B6)

By 2020 the SPT-NGET boundary B6 comprises the Strathaven/Gretna–Harker 400 kV double circuit line, the Eccles-Stella West 400 kV double circuit line, the Harker-Chapelcross 132 kV line, the Harker-Gretna/Hawick 132 kV line, the Eastern HVDC link between Peterhead and Hawthorn Pit, and the Western HVDC link between Hunterston and Deeside. The total transmission capacity over the 400 kV HVAC transmission lines and over the HVDC links is shown in the table below. The resultant SQSS capability of the boundary was derived by assuming that the Eccles–Stella West 400 kV double circuit line is in outage condition. Table B4.3 – MVA Capacity across Boundary B6 Summer

Winter

Total Capacity MVA

8492

9824

SQSS Capability MVA

3712

4284

Eastern HVDC Link

1800

1800

Western HVDC Link

1800

1800

AC Transmission

The initial load flow assessment suggests that transmission capability through the SPT-NGET boundary B6 is around 7.55 GW including contribution of 3.60 GW power transfer over the Eastern and Western HVDC links. This was achieved based on the condition that power transfer through the SHETL-SPT boundary B4 reaches its maximum level of 4.94 GW. Given the load demand level of 6.04 GW and generation capacity of 19.89 GW in the region to the north of the boundary, it is anticipated that approximately 14.02 GW could be exported from units in the region without breaching the NET SQSS criteria. This would permit the connection of 2-3GW of ISLES offshore renewable generation in the region of Hunterston. Should more power be transferred through this boundary, the Gretna-Harker 400 kV line and the Brine Field-Lackenby 400 kV line may experience an overload under N-D outage conditions. Thus, an increase in power transfer through the boundary would require deep reinforcements in both the SPT and NGET transmission networks including construction of new 400 kV power transfer corridors or installation of new HVDC links from Scotland down to the NGET transmission network in England and Wales.

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4.4


NGET NORTH & NORTH-EAST ENGLAND TRANSMISSION NETWORK

Harker 400 kV substation in NGET North & North-East England transmission network, shown in Figure B4.3, was selected as a potential connection point for the ISLES offshore renewable generation due to its proximity to the west coast.

SPT-NGET Boundary B6

Harker

NGET Upper North Boundary B7

Figure B4.3 – Transmission Network at Hark 400 kV Substation

4.4.1

Harker 400 kV Substation

Because of its location in the NGET transmission network, Harker 400 kV substation plays a very import role for bulk power transfer from the SPT transmission network down to the southern NGET transmission network. The Harker-Penwortham 400 kV double circuit line via Hutton and Quernmore 400 kV substations would be the key to the bulk north to south power transfer and to additional generation connection at Harker. No new generation is expected to be connected to Harker by 2020. The initial load flow assessment suggests that around 650 MW-1250 MW of new generation could be connected to Harker. The levels of new generation connection at Harker are mainly dependent upon power transfer levels through the SPT-NGET boundary B6. A 7.55 GW power transfer through the SPT-NGET boundary B6 was assumed in the assessment. Additionally, generation output levels from units in the NGET North & North-East England transmission network also have some impact on the levels of new generation connection at Harker. As increasing power transfer through the SPT-NGET boundary B6 is anticipated with more wind generation connection in Scotland by 2020, the limited transmission capability over the north south power transfer corridors would impose constraints on new generation connection on substations along those power transfer corridors. Thus, the limited generation connection capacity available at Harker would preclude it as a preferred location for connection of the ISLES offshore renewable generation.

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4.4.2


NGET Upper North Boundary (B7)

By 2020 the NGET Upper North boundary B7 comprises the Harker-Hutton-Quernmore 400 kV double circuit line, the Norton-Thornton 400 kV double circuit line via Osbaldwick, the Lackenby-Thornton 400 kV double circuit line, and the Western HVDC link between Hunterston and Deeside. The total transmission capacity over the 400 kV HVAC transmission lines and over the Western HVDC link is shown in the table below. The resultant SQSS capability of the boundary was derived by assuming that the Harker–Hutton 400 kV double circuit line is in outage condition. Table B4.4 – MVA Capacity across Boundary B6

AC Transmission

Summer

Winter

Total Capacity MVA

11940

13900

SQSS Capability MVA

7560

8860

1800

1800

Western HVDC Link

The initial load flow assessment suggests that transmission capability across the NGET Upper North Boundary 7 is around 9.00 GW including contribution of 1.80 GW export over the Western HVDC link. This was achieved based on the condition that power transfer through the SPT-NGET boundary B6 reaches its maximum level of 7.55 GW. Given the load demand level of 9.20 GW and generation capacity of 27.3 GW in the region which is to the north of the NGET Upper North boundary B7, it is anticipated that approximately 18.70 GW could be exported from units in the region without breaching the NET SQSS criteria. Should more power be transferred across the boundary, the Osbaldwick-Thornton 400 kV line and Norton-Thornton 400 kV line will be overloaded under N-D outage conditions. Additionally, the 275 kV network in the NGET Yorkshire transmission network (study zone 8) may also experience an overload under N-1 outage condition. Thus, deep reinforcements including reinforcements on the 275 kV network may be necessary to accommodate more power transfer through the boundary.

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4.5


NGET NORTH-WEST ENGLAND AND NORTH WALES TRANSMISSION NETWORK

The existing Heysham, Penwortham, Deeside, Pentir, and Trawsfynydd 400 kV substations in the NGET North-West England and north Wales transmission network, shown in Figure B4.4, were selected as potential connection points for ISLES offshore renewable generation due to their proximity to the west coast and to the main load demand centres. Power transfer levels through the NGET Upper North boundary B7 will impact generation connection capability at these selected substations. When identifying new generation connection capacity to the selected substations, it is assumed that the maximum and average power transfer through the boundary B7 would reach 8.9 GW and 8.2 GW respectively by 2020 including an 1800 MW power transfer via the Western HVDC link.

Figure B4.4 – NGET North-West England & North Wales Transmission Network

4.5.1

Heysham 400 kV Substation

Heysham 400 kV substation is located on the north south power transfer corridors. There are two nuclear generating units with total capacity of 2406 MW, and offshore wind generation of 140 MW is expected to be connected to Heysham by 2020. The initial load flow assessment suggests that around 200 MW-400 MW of further new generation could be connected to Heysham. The Lister Drive-Birkenhead 275 kV line and the South ManchesterBredbury 275 kV lines impose constraints on the generation connection capacity at Heysham. The following generation developments will impact the generation connection capacity at Heysham:

Round 2 Walney and West Dudden offshore wind generation developments, which amount to 866 MW in total and are supposed to connect to Heysham and Hutton. The connection of the Round 2 offshore wind generation will potentially drive no connection capacity at Heysham and likely require new reinforcements in the NGET North-West England and North Wales transmission network.

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Round 3 Irish Sea offshore wind generation development which would be partially connected to Stanah (1240MW). The connection of the Irish Sea offshore wind would definitely require new reinforcements in the NGET North-West England and North Wales transmission network.

Decommissioning of an existing nuclear generating unit at Heysham. This could result in an increase of 1203 MW new generation connection capacity at Heysham.

Consideration of the above developments leads to the conclusion that there is limited available capacity for new generation connection at Heysham without reinforcements in the NGET North-West England and North Wales transmission network. Because of this, Heysham 400 kV substation is not considered to be a preferred location for connection of the ISLES offshore renewable generation.

4.5.2

Penwortham 400 kV Substation

Similar to Heysham 400 kV substation, Penwortham 400 kV substation is also located on the north south power transfer corridors. No generation is connected to Penwortham by 2020. The initial load flow assessment suggests that around 500 MW-1000 MW new generation could be connected to the Penwortham. The Lister Drive-Birkenhead 275 kV line and the South Manchester-Bredbury 275 kV line impose constraints on more new generation connection capacity at Penwortham. Additionally, Pentir-Trawsfynydd 400 kV line may potentially impose constraints on the generation connection capacity at Penwortham. Furthermore, the generation connection capacity at Penwortham will be affected by the two factors below:

Decommissioning of an existing nuclear generating unit at Heysham. This results in an increase of 1203 MW new generation connection capability.

Connection of the Irish Sea offshore generation development to Stanah (1240MW). This result in a significant reduction in the connection capacity at Penwortham.

The combination of these two factors could provide an increased generation connection capacity at Penwortham up to 800 MW to 1300 MW taking into account the availability factor of offshore wind generation. In this case, Penwortham 400 kV substation may have the potential for partial connection of ISLES offshore renewable generation. Should further new generation connection be considered at Penwortham, reinforcements of the 275 kV network in North-West England and North Wales including upgrading of the 275 kV lines from Penwortham to Capenhurst via Kirkby to 400 kV lines would be necessary. Additionally, strengthening of the 400 kV links from the North-West England and north Wales transmission network to other NGET transmission networks may also be required.

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4.5.3


Deeside 400 kV Substation

Because of its location, Deeside 400 kV substation is a key substation in the NGET North-West England and North Wales transmission network to bulk power transfer from north to south and from east to west in the network. There are four 400 kV double circuit lines which connect Deeside to other 400 kV substations. The total transmission capacity over the transmission lines at Deeside is shown in the table below. The SQSS MVA capability was derived by assuming that the Deeside-Capenhurst 400 kV double circuit line is in outage condition. Table B4.5 – MVA Capacity at Deeside

AC Transmission

Summer

Winter

Total Capacity MVA

20260

22590

SQSS Capability MVA

14000

15950

1800

1800

Western HVDC Link

Approximately 2095 MW of generation is expected to be connected to Deeside by 2020. The initial load flow assessment suggests that only 0 MW - 200 MW of new generation could be connected to Deeside. The limited transmission capacity over the Deeside-Treuddyn Tee 400 kV double circuit line imposes constraints on the generation connection capacity at Deeside. Furthermore, following factors will affect the generation connection capacity at Deeside:

Power transfer levels over the Pentir-Deeside 400 kV double circuit lines, which is associated with new nuclear generation connection at the Wylfa 400 kV substation.

Connection of the Irish Sea offshore wind generation to Wylfa and Deeside. This could require significant deep reinforcements within the NGET North-West England and North Wales transmission network.

Decommissioning of coal generation at Fiddlers Ferry (1.98GW). This should increase the available generation connection capacity at Deeside due to the reduction of power transfer over the 275 kV network between Penwortham and Capenhurst.

4.5.4

Pentir 400 kV Substation

Pentir 400 kV substation is located in the 400 kV ring comprising Pentir, Deeside, Treuddyn Tee and Trawsfynydd 400 kV substations. The 400 kV ring plays an important role for power transfer from Pentir to other substations in the NGET North-West England and North Wales transmission network. There are three 400 kV transmission circuits that are mainly used for power transfer from Pentir to Deeside and to Trawsfynydd and the total transmission capacity over the transmission lines is shown in the table below. The SQSS capability was derived by assuming that the Pentir-Deeside 400 kV double circuit line is in outage condition.

Table B4.6 – MVA Capacity at Pentir

AC Transmission

MDR0707Rp0026 APP B

Summer

Winter

Total Capacity MVA

6020

6780

SQSS Capability MVA

1000

1160

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No generation is considered at both Pentir and Wylfa 400 kV substations by 2020. The initial load flow assessment suggests that around 800 MW - 1000 MW new generation could be connected to Pentir, and that the limited transmission capacity over the Pentir-Trawsfynydd 400 kV line is the key constraint on the Pentir generation connection capacity. The generation connection capacity could be further affected by following developments.

Round 3 Irish Sea offshore wind generation development with 1240 MW partially connected to Wylfa 400 kV substation.

Construction of two nuclear generating units at Wylfa with total capacity of 2870 MW.

Either of these developments would drive the resultant generation connection capacity at Pentir to near-zero and reinforcements may be required in the NGET North-West England and North Wales transmission network including:

Construction of new power transfer corridors from Wylfa to Pentir or to other 400 kV substations. This will ensure a secure connection of nuclear generation and Round 3 Irish Sea offshore wind generation connected to the Wylfa 400 kV substation.

Strengthening of the 400 kV link between Pentir and Trawsfynydd 400 kV substations by building a 400 kV double circuit line. This will increase power transfer capacity over the PentirTrawsfynydd double circuit line and enable more power diversion to the Pentir-Trawsfynydd double circuit line under N-D outage condition.

The limited generation connection capacity available at Pentir precludes it as a suitable location for the connection of ISLES offshore renewable generation.

4.5.5

Trawsfynydd 400 kV Substation

Trawsfynydd 400 kV substation is also located in the 400 kV ring comprising Pentir, Deeside, Treuddyn Tee and Trawsfynydd 400 kV substations. The generation connection capability at Trawsfynydd is dependent upon the transmission capability of the 400 kV ring, of which the SQSS transmission capacity is only 1160/1000 MVA in winter/summer seasons. In addition to the pumped-storage generation at Ffestiniog, which is fed into Trawsfynydd via 275 kV lines, no other generation is expected to be connected to Trawsfynydd by 2020. The initial load flow assessment suggests that around 1250 MW of new generation could be connected to the substation. Generation output levels from units in the NGET North-West England and North Wales transmission network and power transfer levels through the NGET Upper North boundary B7 do not have a significant impact on new generation connection capacity at the substation. The Pentir-Trawsfynydd 400 kV line imposes the main constraint for generation connection capacity at Trawsfynydd. It is anticipated that the new generation capacity at Trawsfynydd would increase after completion of reinforcement on the Pentir-Trawsfynydd 400 kV line. However the impact of this is not obvious due to the combined effect of nuclear generation installation at Wylfa and the connection of the Irish Sea offshore wind generation. As such, Trawsfynydd 400 kV substation may also provide the potential for connection of some level of ISLES offshore renewable generation.

4.5.6

Summary

Investigations of generation connection capacity at the selected 400 kV substations in the region of NGET North-West England and North Wales transmission network suggest that none of the existing 400 kV substations has sufficient connection capacity to accommodate significant levels of additional generation from the ISLES zone without extensive reinforcements.

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Because of the distance from the ISLES zone to the region and from the network of the region to the load centres in south east of England, however, it may be worth considering multiple substations in the region, with extensive reinforcements to enable the connection of significant levels of additional generation from the ISLES zone. For example, connection at Penwortham and Deeside 400 kV substation with extensive reinforcements including:

Installation of another the Pentir-Trawsfynydd 400 kV line and up-rating of the existing PentirTrawsfynydd 400 kV line, enabling significant increase of transmission capacity from Pentir to Trawsfynydd.

Upgrade of the 275 kV lines from Penwortham to Capenhurst via Kirkby to 400 kV. This reinforcement could be utilized to increase transmission capability from Deeside to Penwortham and is extremely important for power division under the Deeside-Daines 400 kV double circuit line outage condition.

Installation of a new South Manchester-Bredbury 275 kV circuit or upgrade of the line to 400 kV, enabling more transmission capability between the East network in Zone 8 and the West network in Zone 9 via the two substations.

Construction of new 400 kV power transfer corridors from Deeside to other 400 kV substations in Zone 11. For example, the new Deeside-Cellarhead 400 kV lines or new HVDC links from Deeside to London load centre.

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4.6


NGET SOUTH WALES AND SOUTHWEST TRANSMISISON NETWORK

Due to its location, the NGET South Wales and Southeast transmission network is not significantly impacted by the bulk north south power transfers on the transmission system. Thus, connection of ISLES offshore renewable generation to the NGET South Wales and Southeast transmission network would not need to share the limited north south power transfer capability with other new generation. The Pembroke and Alverdiscott 400 kV substations in the NGET South Wales and South West transmission network, shown in Figure B4.5, were selected as potential connection points for the renewable generation developments in the ISLES zone due to their locations on the west coast and their relative proximity to the load centre in London.

Figure B4.5 – Transmission Network at Pembroke and Alverdiscott

4.6.1

Pembroke 400 kV Substation

By 2020 there are two 400 kV double circuit lines which connect Pembroke to other 400 kV substations in the rest of the NGET transmission network. The total transmission capacity over the transmission lines at Pembroke is shown in the table below. The SQSS capability was derived by assuming that one Pembroke-Swansea 400 kV double circuit line is in outage condition. Additionally 2000 MW CCGT generation is connected to Pembroke by 2020. Table B4.7 – MVA Capacity at Pembroke

AC Transmission

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Summer

Winter

Total MVA

8880

11110

SQSS MVA

4440

5550

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The initial load flow assessment suggests that no new generation could be connected to Pembroke without up-rating of the Walham-Cowley 400 kV line. After up-rating the Walham-Cowley 400 kV line, up to 1500 MW - 2000 MW new generation could be connected to the substation. The assessment was based on the condition that 100% MW output from Pembroke CCGT units, and 70%~80% MW output from other conventional units in zone 13. Limited transmission capacity over the MelkshamSeabank 400 kV line imposes the main constraint on the generation connection capacity at Pembroke. Though the distances from Pembroke to the ISLES offshore resources are somewhat longer than from other 400 kV substations in Northern England and North Wales, this substation location could still potentially be utilised to facilitate connection of up to 2000 MW of ISLES offshore wind generation should the network in Northern England and North Wales be unable to accept all of the generation export from the ISLES zone.

4.6.2

Alverdiscott 400 kV Substation

The network topology in the NGET South West transmission network suggests that the transmission capacity of 400 kV circuits at Alverdiscott is the key constraint on the levels of new generation connection at Alverdiscott. By 2020 there are two 400 kV double circuit lines that connect Alverdiscott to other 400 kV substations in the NGET Southwest transmission network and the total transmission capacity over the lines is shown in the table below. The SQSS capability was derived by assuming that one Alverdiscott-Taunton 400 kV double circuit line is in outage condition. Table B4.8 – MVA Capacity at Alverdiscott

AC Transmission

Summer

Winter

Total MVA

4440

5560

SQSS MVA

2220

2780

The initial load flow assessment suggests that approximately 2800 MW - 2850 MW of new generation could be connected to the Alverdiscott depending upon generation output levels from generating units at other substations in the network. The generation capacity distribution in the NGET South West transmission network by 2020 is as: 905 MW CCGT generation at Langage, 1261 MW nuclear generation at Hinkley Point, and 140 MW OCGT generation at Indian Queens. The expected 1512 MW offshore wind generation from Bristol Channel was assumed to connect to Hinkley Point 400 kV substation. The limited transmission capacity over the Alverdiscott-Taunton 400 kV lines represents the key constraint on the generation connection capacity at Alverdiscott. The generation connection capacity, however, will also be affected by following factors:

Location at which the Bristol Channel offshore wind generation is connected.

Decommissioning of the existing 1261 MW nuclear generation at Hinkley 400 kV substation

Installation of 4970 MW new nuclear generation at Hinkley Point 400 kV substation

Consideration of these factors suggests that available generation capacity at Alverdiscott may fall to near-zero in the absence of significant new network reinforcements.

4.7

SUMMARY

The minimum and maximum connection capacities for the selected substations in the 2020 timeframe are summarised in Table B4.9 below for each of the four strategic connection areas considered based on their proximity to ISLES resources and the offshore transmission distances for connection.

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It should be noted that the resultant minimum and maximum capacities are based on the background system data extracted from publicly available data sources referenced in the previous sections. Any changes in the system background including connection of new generation or decommissioning of the existing generation at or in the vicinity of the key substations, or introduction of reinforcements of the onshore transmission network around the key substations could result in material changes to the conclusions. Although there are a number of assumptions made, further evaluation is unlikely significantly increase the degree of confidence in the results given the uncertainties associated with future generation and infrastructure development, and as such the analysis summarised here is considered sufficient to meet the requirements of the ISLES study. Table B4.9 – Potential Connection Capacity Range (MW) at Key GB Substations Strategic Connection / Substation Location Northern Scotland Beauly Mid Scotland Hunterston Inverkip Northern England and North Wales Harker Penwortham Pentir Tranwfynydd South Wales / Southern England Pembroke Alverdiscott

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Zone

Lower MW

Upper MW

1

0

700

4 4

2000 1850

3000 2050

7 9 9 9

650 500 800 1250

1250 1000 1000 1250

13 17

0 2200

2000 2850

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B5. ASSESSMENT OF TRANSMISSION CAPABILITY IN THE ALLISLAND SYSTEM IN 2020 The primary load centre for export of the ISLES offshore renewable generation is the GB system. In addition, extensive analysis of the Northern Ireland and Irish Republic networks by TNEI also suggests that these systems are more likely to be sources of onshore renewable generation rather than demand sinks requiring significant onshore connection from the ISLES. As such, detailed transmission network capability was not assessed for the All-Island system. For those substations which could potentially be used for connection of the ISLES offshore renewable generation in the All-Island system, however, their available network capacity can be derived based on the planned network topology and transmission capacity of overhead lines, cables, and transformers. The available network capacity at the substations gives, to some extent, an indication of new generation connection capability.

5.1

TRANSMISSION CAPACITY IN THE REPUBLIC OF IRELAND SYSTEM

The ISLES offshore renewable generation resources off Ireland’s east coast and south-east coast may potentially seek connection to 400/220 kV substations in the Ireland system and then export to the rest of the All-Island system or to the GB system. Due to their locations close to the east coast, 220 kV or 400 kV substations at Louth, Gorman, Woodland, Carrickmines, and Arklow may potentially be used for these connections. The transmission capacity at these substations and at other key substations was estimated and is shown in the table below. The derived transmission capacity was based on the winter MVA rating of transmission circuits and transformers in the substations taking into consideration of the intact system and under N-1 and N-1-1 outage conditions. Table B5.1 – MVA Capacity at Key Substations in the Republic of Ireland System Substations

Louth 220 kV Gorman 220 kV Woodland 400 kV Carrickmines 220 kV Arklow 220 kV Great Island 220 kV Knockanure 220 kV Tarbert 220 kV Cashla 220 kV

Intact System 3941 1536 5032 2479 1613 1481 1536 3079 2217

N-1 Outage 3060 1018 3319 1886 1095 963 1018 2486 1699

N-1-1 Outage 2179 500 1606 1293 577 525 500 1893 1181

Generation Connected

210 MW Wind

The derived MVA capacity of a substation gives indicative information that extra transmission capacity could be used for new generation connection at the substation. However, this does not mean that the system is able to accommodate the same amount of new generation connection. To accommodate the connection of ISLES offshore renewable generation to these substations, it is believed that deep network reinforcements are necessary and detailed system assessment will be required to identify where those deep network reinforcements are required.

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5.2


TRANSMISSION CAPACITY IN THE NORTHERN IRELAND SYSTEM

Three ISLES offshore renewable generation resources off the north coast of Northern Ireland may potentially seek connection to 275 kV substations in the NI system and then export to the rest of the All-Island system or to the GB system. The 275 kV substations at Coolkeeragh, Ballylumford, Kilroot, and Castlereagh may potentially be used for the connection. The transmission capacity at these substations was estimated and shown in the table below. Table B5.2 – MVA Capacity at Key Substations in NI System

Substations Coolkeeragh 275 kV Ballylumford 275 kV Kilroot 275kV Castlereagh 275 kV

Intact System 1506 4004 3524 4484

N-1 Outage 993 3123 2643 3603

N-1-1 Generation Connected Outage 480 292 2242 1128 1762 1204 2722

The derived MVA capacity at the substation does not mean that the system is able to accommodate the same amount of new generation connection. To accommodate ISLES offshore renewable generation connection at these substations, additional network reinforcements in the NI system may be required. The additional network reinforcements may consist of construction of new 275 kV substations which are close to the new renewable generation developments, strengthening of the 275 kV transmission networks between 275 kV substations, construction of new power transfers from substations in Donegal region to substations in the NI transmission network, installation of new interconnectors between the NI and Ireland transmission networks and between the NI and GB transmission networks, etc.

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B6.


REFERENCES

1. National Grid , “2009 Great Britain Seven Year Statement (May 2009)”, http://www.nationalgrid.com/uk/sys_09/copyright.htm 2. ENSG, “‘Our Electricity Transmission Network: A version for 2020’ full report”, ENSGR 2009026, July 2009. 3. National Grid, “National Electricity Transmission System Security and Quality of Supply Standard”, version 2.0, June 24, 2009 4. National Grid, “Transmission Networks – Offshore Development Information Statement”, December 2009. 5. EirGrid, “Transmission development plan 2008 - 2012”, July 2009, www.eirgrid.com 6. EirGrid, “Transmission forecast statement 2010-2016”, version 1.0, December 2009, www.eirgrid.com. 7. EirGrid, “Grid 25 – A Strategy for the Development of Ireland’s Electricity Grid for a Sustainable and Competitive Future”, www.eirgrid.com 8. SONI, “Seven Year Generation Capacity Statement 2010 – 2016”, December 2009. 9. SONI, “Transmission Seven Year Statement 2006/07 – 2012/13”, October 2006. 10. TNEI, “Workstream 3 All-island-Grid Study Report”, December 2007.

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