132kV network reconfiguration to accommodate wider systems works

Transcription

1 July 2012

2 CONTENTS 1. Executive Summary UK Power Networks Business Case Existing network infrastructure Pelham & Wymondley Group Overall assessment P2/6 compliance Transfer of Belchamp Grid to Bramford P2/6 compliance Thaxted & Belchamp Grid Review of Strategic Options...11 Option 1 - Do Nothing...11 Option 2 - Replace 132kV circuits between Twinstead Tee and Burstall Bridge...11 Option 3 - Extension of the 132kV PCB overhead line from Twinstead...13 Option 4-33kV Network Reinforcement...15 Option 5 - Reinforce Braintree GSP and install new 132kV circuits...16 Option 6 - New Grid Supply Point at Twinstead...19 Option 7 - New Grid Supply Point at Coggeshall...20 Option 8 - New Grid Supply Point at Earls Colne Strategic Options evaluation Recommended Option kV Running Arrangement for Twinstead GSP References...25 APPENDIX A1: Eastern Power Networks Distribution area...26 APPENDIX A2: Twinstead GSP proposed locations...27 APPENDIX A3: Summary of strategic options...32 Page 2 of 35

3 Glossary of Terms ACS ACSR Al BR CB CI CML Cu DG DNO DPCR EHV EPN FCO GSP HV kv LV MVA MW NAMP NG NOP OF OFGEM OHL PLE POC RDP RIIO RMS SC SCADA SCO SCP SGT SLD St UKPN Average Cold Spell Aluminum Conductor Steel Reinforced Aluminum British Rail Circuit Breaker Customer Interruptions Customer Minutes Lost Copper Distributed Generation Distribution Network Operator Distribution Price Control Review Extra High Voltage (132 kv) Eastern Power Networks First Circuit Outage Grid Supply Point High Voltage (>11 kv) Kilo Volt: 1000 V Low Voltage Mega Volt Ampere Mega Watt Network Asset Management Plan National Grid Normally Open Point Oil Filled Office of Gas and Electricity Markets Overhead Line Planning Load Estimate Point of Connection Regional Development Plan Revenue = Incentives + Innovation + Outputs Root Mean Square Single Core Supervisory Control and Data Acquisition Second Circuit Outage Single Core Poly Super Grid Transformer Single Line Diagram Steel UK Power Networks Page 3 of 35

4 1. EXECUTIVE SUMMARY National Grid has approached UK Power Networks to request that the 132kV dual circuit overhead line between Twinstead Tee and Burstall Bridge be transferred to National Grid ownership to be dismantled and replaced by a 400kV overhead line. This document provides information to demonstrate what is necessary to allow UK Power Networks to continue to provide a safe and reliable electricity supply to homes and businesses in the area following the transfer of the 132kV dual circuit overhead line along with technical, environmental and economical comparison of alternative reconfigurations or reinforcement options. In addition it details the recommended proposal to construct a new 400/132kV Substation to the West of Twinstead, Essex. The existing 132kV double circuit currently runs open, with the HV bows broken at tower PCB16 in an area known as Burstall Bridge, approximately 3km from Bramford substation. The removal of the 132kV circuits to Bramford will result in an increased risk to the supply of existing customers and UK Power Networks not complying with the distribution networks planning standard P2/6, a requirement by Ofgem for a licence to operate an electricity distribution network. This planning standard requires there to be back up capacity so that if a circuit faults or needs to be closed down for maintenance a second circuit can provide sufficient power based on normal summer usage. The removal of the existing line results in insufficient 33kV transfer capacity to cater for a summer second circuit outage (N-2) of the 132kV overhead line between Pelham and Thaxted Grid. It is also expected that Belchamp Grid will be transferred to Bramford GSP on a permanent basis to maintain P2/6 compliance as the 132kV circuit from Belchamp Tee to Bramford already provides the required transfer capability Each potential option has been assessed to ensure that it meets the need case to provide an alternative supply to the existing 132kV circuits, that the resultant distribution system is compliant with the various statutory and licence obligations and does not leave UK Power Networks customers at a greater risk. It has been confirmed that a new Grid Supply Point (GSP), a substation where UK Power Networks takes energy from National Grid at 400kV and steps it down to 132kV for distribution locally, in the vicinity of Twinstead is the appropriate distribution network reinforcement that should be considered in the context of transferring the existing 132kV overhead line between Twinstead Tee and Burstall Bridge. It has been determined that a 400/132kV Super Grid Transformer (SGT) connected to a single section 132kV busbar via a SGT LV circuit breaker with two 132kV feeder circuit breakers to the existing 132kV OHL is the preferred initial configuration for Twinstead GSP, to be designed to accommodate future expansion as the DNO network evolves. It is proposed to run the new GSP in parallel to Pelham with the bus coupler open at Pelham Grid Supply Point. Page 4 of 35

5 2. UK POWER NETWORKS BUSINESS CASE 132kV network reconfiguration to UK Power Networks (EDF Energy Networks at the time) were requested to undertake an investigation into whether the ownership of the 132kV double circuit overhead line could be transferred to National Grid. An initial report was produced by UK Power Networks in 2009 which identified several viable solutions and served as the basis for route feasibility studies. Initial results recommended the transfer of Belchamp and Thaxted Grid to the new GSP, equipped with a 132kV double busbar and supplied by two 400/132kV 240MVA Super Grid Transformers (SGT). This configuration is reviewed as part of this document in light of further information regarding planned modifications to the 400kV network and the impact of a revised 132kV running arrangement on the distribution network. The UKPN business case supersedes the previous reports and is built around the following structure: Section 2 Brief explanation of the 132kV and 33kV network for the Pelham/Wymondley GSP group; Reasoning behind reinforcement projects currently in the NAMP plan; Compliance issues arising from the transfer and removal of the 132kV circuits between Twinstead Tee and Burstall Bridge; Section 3 Review of strategic options; Section 4 Evaluation of the strategic options; Recommended option for a new 400/132kV GSP near Twinstead; Technical assessment of the different configurations and running arrangements for Twinstead; 2.1 Existing network infrastructure Due to the predominantly rural nature of this area of North Essex, especially in the vicinity of Twinstead and Castle Hedingham, the distribution network is predominantly radial with long lengths of 11kV overhead line supplied from small/medium size primary substations with firm capacity below 24MVA such as Cornard, Halstead and Wethersfield primaries and larger load centres in the towns of Sudbury, Haverhill and Saffron Walden. These primaries are fed from three different Grid substations of Braintree, Belchamp and Thaxted and are part of two different GSP groups of Pelham - Wymondley and Braintree. 770/843 A 176/193 MVA <PCB211> <PCB273> <PCB323> <PCB5> Figure 1. Pelham & Wymondley - Existing network (Conceptual schematic) Braintree GSP is equipped with 2x240MVA 400/132kV SGT and is interconnected with Rayleigh GSP via a double circuit 132kV overhead line fitted with 175mm 2 ACSR conductors (PSB-PSA) with a 2.2km section of 500mm 2 OF Cu cable and supplies Braintree local (2x90MVA), Chelmsford North (2x30/30MVA), Chelmsford East no2 (1x90MVA) and BR Springfield (1 x 14MVA) rail load. Braintree forms a P2/6 Class D with an average cold spell (ACS) maximum Page 5 of 35

6 winter corrected demand in of 168.8MW in winter 2010/11. According to the Planning Load Estimates (PLE) the demand is expected to reach 190.7MW in 2021/22. Pelham GSP is equipped with 2x240MVA 400/132kV SGT and supplies Bishop s Stortford Grid (2x90MVA) via an underground circuit directly off the 132kV bars and Rail supply (1 x 14MVA), Thaxted Grid (2x90MVA) and Belchamp Grid (4 x 45MVA) from a 132kV double circuit overhead line to the east (SMA1-7 and PCB234-PCB118). Pelham GSP is interconnected with Wymondley GSP to the west by approximately 26km of double circuit 132kV overhead line fitted with 175mm 2 ACSR conductors (PCB), circuit no1 tee off to Melbourn Grid (1x45MVA) at tower PCB273 and circuits no1+2 tee off to Stevenage Grid (2x90MVA ). Wymondley GSP is equipped with 2x240MVA 400/132kV SGT and supplies Wymondley Grid (2x90MVA) and Letchworth Grid (2x90MVA). PCB double circuit 132kV overhead line extends to the east from Pelham to Bramford, teeing off to Cliff Quay Grid and Lawford 132kV switching station. This 132kV circuit is made up of two types of OHL conductors. A 17.5km of 400mm 2, rated at 745/925A, runs between Pelham and Thaxted (to a pair of circuit breakers) and feeding Thaxted Grid and the rail track supply point. The 34.3km section from Thaxted is made up of 175mm 2 and is connected to two Bramford circuits at tower PCB5: 1. Circuit number 1 (PCB No1) is connected to the 300mm 2 Cliff Quay 4 OHL; 2. Circuit number 2 (PCB No2) is connected to the 300mm 2 Lawford 4 OHL; Currently this section of the circuit runs open, with the HV bows broken at tower PCB16 in an area known as Burstall Bridge, approximately 3km from Bramford substation. This configuration can be altered as part of outage planning scenarios when required. The 132kV route crosses the NG 400kV circuits of Bramford-Rayleigh and Pelham-Rayleigh near the village of Twinstead. The existing 132kV double circuit provides up to 198/246MVA of transfer capacity (summer/winter on a double 132kV circuit) between Pelham-Wymondley Group and Bramford, sufficient to provide a firm supply to Thaxted and Belchamp Grid substations. 2.2 Pelham & Wymondley Group Overall assessment Overall Pelham - Wymondley network comprises seven 132/33kV Grid substations with associated 33/11kV primary substations and a 132/25kV Grid substation which form a P2/6 Class E supply group with an average cold spell (ACS) maximum winter corrected demand of 492.6MW in winter 2010/11. According to the 2011 Planning Load Estimates (PLE) the demand is expected to reach 591MW in 2021/22 (figure 2). MW Pelham and Wymondley Actual Predicted 05/06 07/08 09/10 11/12 13/14 15/16 17/18 19/20 21/22 23/24 25/26 Year Figure 2. Pelham & Wymondley - Winter Maximum Demand (Actual and Predicted) Page 6 of 35

7 The minimum demand to be met in this group under outage conditions is detailed in the P2/6 table below Circuit outage First circuit outage Second circuit outage Minimum demand to be met for a class E (between 300MW and 1500MW) Immediately: Group demand 492.6MW Immediately: All consumers at 2/3 Group Demand 328.4MW Within time to restore arranged outage: Group Demand 492.6MW The existing network is in compliance with P2/6 security of supply. The 132kV circuits between Pelham and Bramford run normally open at the tower PCB16 and this configuration can be altered by making the HV bows on the tower as part of pre outage planning scenarios to guarantee supply to the group while works on other 132kV sections are taking place, a situation that will occur more frequently as the load in the system increases. A P2/6 assessment of the existing running arrangement has been carried out for various winter First Circuit Outage (FCO) and summer Second Circuit Outage (SCO) taking into account the predicted loads up to 2020 as per the table below. P2/6 Scenario Exit Point Fault scenario First Circuit Outage (FCO) Winter maximum demand Second Circuit Outage (SCO) Summer maximum demand Pelham 132kV Wymondley 132kV Pelham Wymondley 132kV circuit Pelham Thaxted 132kV circuit Pelham 132kV Wymondley 132kV Pelham Wymondley 132kV circuit Pelham Thaxted 132kV circuit SGT1 or SGT 2 out SGT1 or SGT 2 out Circuit number 1 fault Circuit number 2 fault Circuit number 1 fault Circuit number 2 fault SGT1 on outage and SGT 2 on fault SGT1 on outage and SGT 2 on fault Loss of circuit no.1 and no.2 Loss of circuit no.1 and no.2 A summary of the findings is available in the table below: Study Result Base Case - Existing network Solid running arrangement at Pelham Fault level assessment Load flow Normal running No significant issues arise for both 3 phase and earth fault studies. Stevenage Grid 3 phase peak make is within 90% of the switchgear rating. No issues of note 3 phase and earth fault at Pelham 132kV above switchgear rating for both peak make and RMS break. No issues of note P2/6 assessment The loss of Pelham SGT1 results in 851A (97% rating) flowing between Pelham and Wymondley 132kV ; Study not carried out due to fault level constraints Page 7 of 35

8 FCO Winter 2017/18 P2/6 assessment SCO Summer 2016 The loss of Wymondley SGT results in a 105% load on the remaining SGT, but still within the cyclic rating; The loss of Pelham - Thaxted 132kV circuit result in 843A (91% rating) for the remaining circuit. This value is expected to increase to 921A in winter 2021/22 thus requiring the transfer of Belchamp Grid to Bramford GSP (figure 4). The loss of a Pelham SGT coincident with an outage on the remaining SGT results in the overload of the 132kV circuit between Stevenage Tee and Melbourn Tee and the overload of the 132kV circuit between Stevenage Tee and Pelham (figure 3) The loss of a Wymondley SGT coincident with an outage on the remaining SGT results in the overload of the 132kV PCB OHL between Pelham and Melbourn Study not carried out due to fault level constraints WYMONDLEY GRID 132/33kV S/S LETCHWORTH 132/33kV S/S WYMONDLEY GSP 400/132kV S/S 2x240MVA SGT 799/875 A 181/199 MVA 751 A 679 A STEVENAGE 132/33kV S/S MELBOURNE 132/33kV S/S 517 A 354 A NO A 153 A NO A 433/539 A 99/123 MVA NO.2 PELHAM GSP 400/132kV S/S 2x240MVA SGT 112 A 123 A BISHOPS STORTFORD 132/33kV S/S 290 A NO.2 Figure 3. P2/6 assessment for SCO in Summer kV BR UGLEY THAXTED 132/33kV S/S 745/925 A 172/211 MVA 156 A BELCHAMP 132/33kV S/S 433/539 A 99/123 MVA HV Bows Off 2.3 P2/6 compliance Transfer of Belchamp Grid to Bramford The combined demand of Thaxted and Belchamp is expected to increase due to new developments, in particular due to connection activity and developments at Haverhill and Sudbury, supplied from Belchamp Grid. The 400mm 2 section of the PCB circuit between Pelham and Thaxted is rated at 211MVA and the 2010 combined demand reached 163MVA in winter 2010/11. According to the estimates, the demand will reach the circuit capacity in 2021/22. WYMONDLEY GRID 132/33kV S/S LETCHWORTH 132/33kV S/S WYMONDLEY GSP 400/132kV S/S 2x240MVA SGT 799/875 A 181/199 MVA 265 A 540 A STEVENAGE 132/33kV S/S MELBOURNE 132/33kV S/S 227 A 337 A 433/539 A 99/123 MVA NO.1 NO.2 PELHAM GSP 400/132kV S/S 2x240MVA SGT 112 A 123 A BISHOPS STORTFORD 132/33kV S/S 921 A 25kV BR UGLEY Figure 4. N-1 scenario for winter 2021/22 demand (estimate) NO.1 NO.2 THAXTED 132/33kV S/S 745/925 A 172/211 MVA 465 A BELCHAMP 132/33kV S/S 433/539 A 99/123 MVA HV Bows Off Page 8 of 35

9 It is expected that Belchamp Grid will be transferred to Bramford GSP on a permanent basis to maintain P2/6 compliance and the 132kV circuit from Belchamp Tee to Bramford already provides the required transfer capability. P2/6 studies of the Wymondley/Pelham group for an estimated winter maximum demand in 2017/18 show that the loss of one SGT at Wymondley results in an increase in demand from the remaining unit to 255MVA, above the continuous rating of the SGT but still within the 6h cyclic rating of 275MVA. According to the estimates this value will be reached in 2023/24. If the option of transferring the Belchamp load to Bramford is removed (along with the Twinstead to Bramford 132kV OHL) additional Supergrid Transformer capacity will be required in the Wymondley Pelham Group. 2.4 P2/6 compliance Thaxted & Belchamp Grid The combined winter demand of Thaxted and Belchamp is classed as group D under ENA recommendation P2/6 security of supply, with a peak demand of 163MW as seen on the 132kV circuits from Pelham GSP in 2010 (20 th December). At present there is no generation connected at 33/132kV in the area to be taken into account and there is limited interconnection to Thaxted and Belchamp Group to support the load in the event of summer N-2 scenario for the loss of the 132kV circuits between Pelham GSP and Thaxted. The minimum demand to be met in this group under outage conditions is detailed in the P2/6 table below: Circuit outage First circuit outage Minimum demand to be met for a class D (between 60MW and 300MW) Immediately: Group demand minus up to 20MW (automatically disconnected) 143MW (winter demand 20MW) Within 3 hours: Group Demand 163MW Second circuit outage Within 3 hours: Smaller of Group demand minus 100MW or 1/3 Group demand 54.3MW (1/3 of Winter demand) Within time to restore arranged outage: Group Demand Network modelling results are shown below, for a N-2 scenario for the 132kV circuits between Pelham and Thaxted with a combined demand of 103.7MVA equivalent to 2011 summer maximum demand. This scenario results in the loss of Thaxted, Belchamp and a rail supply incoming circuits and enabling the backfeed by series of remote/manual switching on the 33kV network to supply the affected areas from Bury, Braintree and Stowmarket Grid substations. Belchamp Grid A total of 22.5MVA demand can be permanently supported for a N-2 on the 132kV circuits from Pelham to Thaxted Grid via switching of the normal open points, excluding the demand from Groton T2 and Boxted T1 which is normally supplied from Bury Grid and Stowmarket Grid: 16.5MVA support available from Bury Grid on the Boxted T2 single circuit by remote control of 33kV circuit breakers and manual switching of the 33kV isolators. Circuit total length via Boxted Primary is 23km and via Drinkstone tee is 42km. 6MVA support available from Stowmarket Grid on the Hadleigh T1 / Groton T1 single circuit by manual switching of 33kV disconnector. 33kV total circuit length via Groton Primary is 24km. A total of 38.4MVA demand can be temporarily supported via rota shed. This includes the town of Haverhill and Sudbury. Page 9 of 35

10 Thaxted Grid A total of 30MVA demand can be permanently supported for a N-2 of the 132kV circuits from Pelham to Thaxted Grid: 14.2MVA support available from Braintree Grid on the Halstead tee/wethersfield dual circuit by manual switching of 33kV isolators. 33kV total circuit length via Wethersfield Primary is 26km. 15.8VA support available from Braintree Grid on the West Braintree / Dunmow Primary dual circuit by manual switching of 33kV. 33kV total circuit length via Dunmow tee is 26.5km. A total of 12.7MVA demand can be supported temporarily via rota shed for Saffron Walden and Acrows primaries. In summary, a total of 52.5MVA demand can be permanently supported following a series of manual and remote switching. This equates to approximately 48.5MW which is below the requirements of P2/6 of 54.3MW. The removal of the 132kV circuits to Bramford will result in insufficient 33kV transfer capacity to cater for a summer second circuit outage (N-2) of the SMA/PCB overhead line between Pelham and Thaxted Grid and P2/6 non compliance of the Thaxted and Belchamp group. In addition, UKPN cannot guarantee that the required Grid substations and all seven 33kV circuits mentioned above will be available to support the required demand and that the voltage on the 11kV feeders, emanating from the substations supplied via rota shed, will be within limits. The figure below illustrates the areas normally supplied from Belchamp and Thaxted Grid and the effect of a 132kV N-2 scenario in terms of areas that can be permanently supplied or areas under rota shed (4h supply rota to individual primary substations). This result in the loss of the rail supply and approximately 35,180 customers supplied via rota shed and a substantial impact in the towns of Haverhill, Sudbury and Saffron Walden with a combined population above 50,000. Areas supplied via rota shed (4h) Areas supplied via 33kV backfeed from other Grid substations WRATTING HAVERHIL ACROWS SAFFRON WALDEN WIXDE PUMPING SUDBURY 132kV N-2 Figure 5. Effect of a 132kV N-2 scenario in Belchamp and Thaxted areas (Simplified to show the affected area) Page 10 of 35

11 3. REVIEW OF STRATEGIC OPTIONS UK Power Networks investigated several options that could resolve the predicted compliance issues. The range of options considered at the initial investigation stage included the creation of a new Grid Supply Point as well as the extension of the 132kV network infrastructure and will be the subject of a revaluation as part of this briefing paper. A summary of the following options is available in Appendix A3: Reference Option 1 Option 2 Option 3 Option 4 Option 5 Option 6 Option 7 Option 8 Option Do Nothing Replace 132kV circuits between Twinstead and Burstall Bridge Extension of the 132kV PCB overhead line from Twinstead Twinstead Lawford 132kV substation (New 132kV OHL circuits) Twinstead Lawford 132kV substation (New 132KV UG circuits) Twinstead Abberton Grid (New 132kV OHL circuits) Twinstead Abberton Grid (New 132KV UG circuits) 33kV Network Reinforcement 4.1 Resolve 33kV circuit constraints 4.2 Increase 33kV interconnection Reinforce Braintree GSP and install new 132kV circuits to Rushley Green kV Braintree Rushley Green (New 132kV OHL circuits) kV Braintree Rushley Green (New 132KV UG circuits) kV Braintree Abberton teed off to Twinstead (New 132kV OHL circuits) kV Braintree Abberton teed off to Twinstead (New 132KV UG circuits) New Grid Supply Point at Twinstead New Grid Supply Point at Coggeshall 7.1 New Grid Supply Point at Coggeshall (New 132kV OHL circuits) 7.2 New Grid Supply Point at Coggeshall (New 132KV UG circuits) New Grid Supply Point at Earls Colne 8.1 New Grid Supply Point at Earls Colne (New 132kV OHL circuits) 8.1 New Grid Supply Point at Earls Colne (New 132KV UG circuits) Option 1 - Do Nothing This option covers UK Power Networks transfer of the 132kV circuits between Twinstead and Burstall Bridge without appropriate distribution network reinforcement in place. The existing 132kV double circuit provides up to 198/246MVA of transfer capacity (summer/winter on a double 132kV circuit) between Pelham-Wymondley Group and Bramford, sufficient to provide a firm supply to Thaxted and Belchamp Grid substations and maintain both Grid substations supplied during 132kV outage scenarios. This option has been rejected because it would be in breach UKPN s distribution licence condition in terms of security of supply as it results in P2/6 non compliance of the class D group. The current infrastructure is unable to permanently support the demand at Belchamp and Thaxted Grids without the backup offered by the 132kV circuits to Bramford and would increase the risk of loss of supply to the existing customers. Option 2 - Replace 132kV circuits between Twinstead Tee and Burstall Bridge Option 2 would maintain the existing N-1 transfer capacity between Pelham and Bramford by the replacement of an existing 26km of 132kV double circuit overhead line with two 132kV underground circuits to PCB5 near Bramford GSP. Page 11 of 35

12 As a minimum, this connection would be of similar length to the existing overhead line if completed along the same 26km route, the majority of which is in the Dedham Vale area of outstanding natural beauty and within the wider area of the Stour Valley. This option involves: a. Installation of two 132kV circuits, made up of single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation, along a 26km route, partial in carriage way ; b. 6 directional drill; c. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; d. Modification to the existing 132kV OHL near Bramford; Summary of Option 2 Route length 26km (minimum); Capacity available through connection: 214/252MVA; Environmental and ecological issues: o Within the Stour Valley area. o Dedham Vale area of outstanding natural beauty; o Close proximity to ancient woodlands; o Identified archaeological areas; Special Engineering Difficulties o River crossings: Stour, Brett and Belstead; o Major roads: A131, A134, A1071; o Network Rail: Sudbury to Marks Tey rural line; Requires route feasibility study. This option allows for the transfer of Belchamp Grid to Bramford GSP and the consequential upstream reinforcement at Bramford GSP and the Bramford to Lawford 132kV OHL circuit as per the current infrastructure development plan. Current estimate cost of reinforcement works at Bramford is 12.8m for reinforcing the 132kV circuit from Lawford to Bramford and 45m for 132kV switchgear replacement due to fault level. Estimate cost 45.3m Estimate total cost including reinforcement works at Bramford is 103m Estimate time to implement 5-6 years (2 years consents negotiations, 3-4 years approval + construction) Figure 6. Simplified single line diagram for Option 2 This option has been discounted due to the high cost, environmental impact, complex wayleave negotiations and long timescale. Page 12 of 35

13 Option 3 - Extension of the 132kV PCB overhead line from Twinstead Option 3 would maintain the existing N-1 transfer capacity between Pelham and Bramford by the replacement of the existing 24km of 132kV double circuit overhead line with two 132kV circuits to Lawford or Abberton Grid. The connection to Lawford 132kV will ultimately increase the demand at Bramford by approximate 100MVA and above the current firm capacity of 829MW therefore the planned capacity increase by National Grid at Bramford for a 5 th SGT will be required before Belchamp grid can be transferred. Option 3.1 Twinstead Lawford 132kV substation To fully implement option 3.1, new 132kV circuits are required between Twinstead and Lawford 132kV. This option involves: a. Installation of two 132kV circuits along a 24km route. Option is for an overhead line route with 175mm 2 conductors each capable of 99/123MVA; Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation, 30% in carriage way; b. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; c. Modification to the existing 132kV OHL near Bramford; Summary of Option and Route length 24km (minimum). Route initially assessed; Capacity available through connection: 198/246MVA (OHL) or 214/252MVA (UG); Wayleave consents are required; Environmental and ecological issues: o Close proximity to Dedham Vale area of outstanding natural beauty; o Close proximity to Ancient woodland areas and identified archaeological areas; Special Engineering Difficulties o River crossings: Colne; o Major roads: A12, A134, A137; o Network rail: Norwich London Liverpool street main line and Sudbury Marks Tey rural line. This option allows for the transfer of Belchamp Grid to Bramford GSP and the consequential upstream reinforcement at Bramford GSP and the Bramford to Lawford 132kV OHL circuit as per the current infrastructure development plan. Current estimate cost of reinforcement works at Bramford is 12.8m for reinforcing the 132kV circuit from Lawford to Bramford and 45m for 132kV switchgear replacement due to fault level. Option kV Overhead line Estimate cost 22.6m Estimate total cost including reinforcement works at Bramford is 80.5m Estimate time to implement 6-7 years (2-3 years consents negotiations, 3-4 years approval + construction) Option kV Underground cable Estimate cost 40.1m Estimate total cost including reinforcement works at Bramford is 98m Estimate time to implement 5-6 years (2 years consents negotiations, 3-4 years approval + construction) Page 13 of 35

14 Figure 7. Simplified single line diagram for Option 3.1 Option 3.2 Twinstead Abberton Grid To fully implement option 3.2, new 132kV circuits are required between Twinstead and Abberton 132kV. This option involves: a. Installation of two 132kV circuits along a 22km route. Option is for an overhead line route with 175mm 2 conductors each capable of 99/123MVA; Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation, 20% in carriage way; b. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; c. Modification to the existing 132kV OHL near Bramford; Summary of Option and Route length 22km (minimum). Route initially assessed. Capacity available through connection: 198/246MVA (OHL) or 214/252MVA (UG); Environmental and ecological issues: o Close proximity to the Dedham vale area of outstanding natural beauty; o Close proximity to Ancient woodland areas and identified archaeological areas; Special Engineering Difficulties o Crossing of the Bramford Rayleigh Pelham 400kV circuit; o River crossings: Colne and Roman; o Major roads: A12, A1124 A120, A1071; o Network rail: London Liverpool street main line and Sudbury Marks Tey rural line. A detailed assessment is required to identify reinforcement of the 132kV circuits and increased SGT capacity on the Bramford/Rayleigh group depending on the location of the 132kV injection at Colchester. Estimate cost of reinforcement works at Bramford is 12.8m for reinforcing the 132kV circuit from Lawford to Bramford and 45m for 132kV switchgear replacement due to fault level. Estimate costs for reinforcement of the 132kV circuits to Rayleigh is 50m. Option kV Overhead line, Estimate cost 21.3m Estimate total cost including reinforcement works at Bramford is 79m Estimate total cost including 132kV reinforcement works towards Rayleigh is 75m Estimate time to implement 6-7 years (2-3 years consents negotiations, 3-4 years approval + construction) Option kV Underground cable, Estimate cost 38.5m Page 14 of 35

15 Estimate total cost including reinforcement works at Bramford is 96m Estimate total cost including 132kV reinforcement works towards Rayleigh is 92.5m Estimate time to implement 5-6 years (2 years consents negotiations, 3-4 years approval + construction) Figure 8. Simplified single line diagram for Option 3.2 Option 4-33kV Network Reinforcement The loss of the 132kV circuits to Bramford GSP results in a P2/6 non compliance due to insufficient backup available from the 33kV network to support the demand of Belchamp and Thaxted Grid. A total of 50.6MVA demand can be permanently supported following a series of manual and remote switching, equating to approximately 48.5MW of demand as detailed in section 4.4. The distribution network in the area is limited in its extent and the backup is restricted by voltage drop on the 33kV network and the thermal rating of three overhead circuits which originate from Bury and Stowmarket Grids, a distance of approximately 23km and 24km respectively. From Bury Grid: 33kV OHL Bury Grid Tee to Boxted (pole 1-8): 0.2Cu rated at 425/530A (summer/winter); 33kV OHL Bury Grid to Boxted (pole 8-145): 0.2Cu rated at 425/530A; 33kV OHL Boxted to Belchamp Grid (pole ): 0.2Cu rated at 425/530A; 33kV OHL Bury Grid to Hadleigh (pole 24S-29): 0.1Cu rated at 269/336A; 33kV OHL Bury Grid/Hadleigh to Groton/Cornard Tee (pole1-116): 0.15Cu rated at 382/476A; 33kV OHL Groton to Cornard (pole ): 0.2Cu rated at 425/530A; From Stowmarket Grid: 33kV OHL Stowmarket to Hadleigh (pole 1-115, pole and pole ): 0.1Cu rated at 269/336A; From Braintree Grid: 33kV OHL Braintree Grid to West Braintree (pole ): 0.1Cu rated at 269/336A; Page 15 of 35

16 33kV circuit restrictions 132kV N-2 Figure 9. 33kV circuit restrictions Option 4.1 Resolve 33kV circuit constraints The 33kV network is restricted by the long length and small section of overhead line to Grid sources that form part of different supply groups. An option to resolve the 33kV constraints would be to replace the existing small conductors with larger ones, capable of providing extra capacity and with lower impedance that would result in increased voltage support. This option would involve installing remote switching in the network and replacing the limiting overhead line circuits. Estimate total cost of reinforcement at 33kV is 9.4m. Studies suggest that completing the above works would resolve the circuit overloads and provide 7MVA of additional capacity, capable of supporting the demand increase up to 2017 but would result in 11kV voltage outside of statutory limits at Haverhill (10.3kV) and Cornard (10.17kV). This option has been discounted due to technical constraints in particular 300mm 2 construction or upgrade, voltage limitations, inability to permanently supply Haverhill, Sudbury and Saffron Walden for a N-2 on the 132kV OHL and is seen as a loss of capacity when compared to the capacity provided by the existing 132kV circuits. Option 4.2 Increase 33kV interconnection 33kV interconnection from Belchamp and Thaxted can be enhanced by constructing new 33kV interconnectors. There are several projects within UKPN investment plan to provide additional circuits and improve the resilience of the network within the area and enhance 33kV interconnection. Estimate total cost of reinforcement at 33kV is 20m. Like option 4.1, the increase in interconnection would resolve the immediate issues but won t provide sufficient capacity to cater for the developments expected in the area. This option has been discounted due to technical constraints (voltage limitations), inability to permanently supply Haverhill, Sudbury and Saffron Walden for a N-2 on the 132kV OHL and limited capacity increase. Option 5 - Reinforce Braintree GSP and install new 132kV circuits Option 5 would maintain the existing N-1 transfer capacity between Pelham and Bramford by the replacement of the existing 26km of 132kV double circuit overhead line with two 132kV circuits to Braintree GSP. Page 16 of 35

17 To provide capacity and enable the permanent transfer of Belchamp Grid, to resolve the predicted P2/6 noncompliance, a 3 rd 400/132kV Super Grid Transformer (SGT) is required at Braintree. Currently the winter maximum demand is 168.8MW and the addition of Belchamp Grid will increase this value to 250MW, above the nominal rating of an SGT. As a class D group the requirement under an FCO is to maintain the total demand minus 20MW which is still above a single SGT rating. Common works for option 5: a. Modifications to the 400kV arrangement at Braintree by National Grid; b. Installation of a 3 rd 400/132kV SGT by National Grid; c. Installation of two 132kV circuit breakers and associated equipment; Estimate cost for substation reinforcement works 32m Estimate time to implement 4 years (1 year approvals, 1 year enabling works, 2 year construction) Option 5.1 New 132kV dual circuits between Braintree and the 132kV PCB OHL To fully implement option 5.1, new 132kV circuits are required between Braintree GSP and the PCB overhead line. A desktop route feasibility study was done in 2010 in response to National Grid East Anglia generation connection enquires which indentified several overhead line routes. This option involves: a. Installation of two 132kV circuits between Braintree and the 132kV PCB OHL: Option is for a overhead line with 175mm 2 conductors each capable of 99/123MVA along a 18km route; Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along a 17km route, 50% in carriage way; b. For the underground solution: 5 directional drills; c. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; d. Modification to the existing 132kV OHL near Bramford; Summary of Option 5.1 Route length: OHL 18km or UG (17km) minimum. OHL route initially; Capacity available through connection: 198/246MVA (OHL) or 214/252MVA (UG); Environmental and ecological issues: o Close proximity to Ancient woodland areas; o Identified archaeological areas; Special Engineering Difficulties o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; Reinforcement at Braintree has been identified following the connection to the 132kV PCB circuit. Option kV Overhead line Estimate cost 17.0m Estimate total cost including reinforcement works at Braintree is 49m Estimate time to implement 5-6 years (2-3 years consents negotiations, 2-3 years approval + construction) Option kV Underground cable Estimate cost 30.4m Estimate total cost including reinforcement works at Braintree is 62.4m Estimate time to implement 5-6 years (2-3 years consents negotiations, 2-3 years approval + construction) Page 17 of 35

18 Figure 10. Simplified single line diagram for Option 5.1 and 5.2 This option has been discounted due to the high cost, high risk factor (archaeological and environmental), complex wayleave negotiations and long timescale. Option 5.2 New 132kV circuits between the Braintree-Abberton circuit and Twinstead To fully implement option 5.2, new 132kV overhead line circuits are required between Coggeshall and the PCB circuits. A desktop route feasibility study was done in 2010 in response to National Grid East Anglia generation connection enquires which indentified several overhead line routes. This option involves: a. Installation of two 132kV circuits between Coggeshall and Rushley Green: Option is for a overhead line with 175mm 2 conductors each capable of 99/123MVA on a 17.5km route; Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along an 18km route, 40% in carriage way; b. For the underground solution: 5 directional drills; c. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; d. Modification to the existing 132kV OHL near Bramford; Summary of Option 5.2 Route length 17.5km (minimum). OHL route initially assessed, underground route is largely unexplored; Capacity available through connection: 198/246MVA (OHL) or 214/252MVA (UG); Wayleave consents are required; Environmental and ecological issues: o Close proximity to Ancient woodland areas; o Identified archaeological areas; Special Engineering Difficulties o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; Reinforcement at Braintree has been identified. Option kV Overhead line Estimate cost 16.5m Estimate total cost including reinforcement works at Braintree is 46.5m Estimate time to implement 5-6 years (2-3 years consents negotiations, 2-3 years approval + construction) Page 18 of 35

19 Option kV Underground cable Estimate cost 31.0m Estimate total cost including reinforcement works at Braintree is 63m Estimate time to implement 5-6 years (2-3 years consents negotiations, 2-3 years approval + construction) Braintree GSP Coggeshall Grid New Figure 11. Simplified single line diagram for Option 5.1 and 5.2 (132kV connections shown) This option has been discounted due high risk factor (archaeological and environmental), complex wayleave negotiations, long timescale and public awareness of new 132kV overhead lines. Option 6 - New Grid Supply Point at Twinstead Option 6 proposes the creation of a new Grid Supply Point near Twinstead, adjacent to the 400kV circuits Bramford- Pelham and in close proximity with the Thaxted to Bramford 132kV circuits. To fully implement this option, a short length of 132kV cables is required to pick up the 132kV. This option involves: a. Creation of a 400/132kV Grid Supply Point; b. Installation of 400/132kV SGT by National Grid. Further information on 6.1; c. Installation of 132kV switchgear. Further information on 6.1; d. Installation of two 132kV underground circuits between the substation and the 132kV circuits; e. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; f. Modification to the existing 132kV OHL near Bramford; Summary of Option 6 132kV Route length between 200m and 1.5km, dependant on the site location; Capacity available through connection: 198/246MVA (restricted by the existing 132kV OHL circuit); Wayleave consents are required for site 3; Environmental and ecological issues: o Close proximity to Ancient woodland areas; Special Engineering Difficulties o No major engineering difficulties indentified. This option has been previously discussed with National Grid who appointed TEP to undertake an environmental and planning assessment of the feasibility of sitting a new Grid Supply Point between Twinstead Tee and Thaxted. Out of a total of 9 potential sites, the study identified 3 sites to further investigate. Page 19 of 35

20 Twinstead GSP Figure 12. Simplified single line diagram for Option 6 including the 3 identified sites GSP Site 1 Butlers Wood and Waldegrave Wood: The 400kV overhead line runs between the two woodlands and there is insufficient space for the GSP beneath the line but potential sites have been identified in the immediate vicinity of the overhead line and directly accessible from the A131. The dense woodland at Butlers and Waldegrave Wood offers screening potential. This site is the furthest away from the 132kV overhead line, approximately 1.5km. GSP Site 2 Delvyns Lane: This site is adjacent to Ramacre Wood approximately 1.5km to the north east of Castle Hedingham and is a field currently used for pasture. The site is sufficiently sized to accommodate the footprint of the GSP. The existing 400kV overhead line passes to the north of Ramacre Wood and the 132kV overhead line crosses the south west corner of the site. GSP Site 3 Colne Valley Farm Park: A site adjacent to the A1017 on the fringes of urban development at Castle Hedingham and adjacent to the existing overhead line to the north of Colne Valley Farm Park, a tourist attraction featuring rare breeds and including a woodland picnic area and a walk along the River Colne. A flood risk zone associated with the river covers part of the site. Both the 400kV and the 132kV OHL are located in the vicinity. Estimate cost for UK Power Networks elements: Site 1: 3.6m (2x1000mm 2 Al 132kV underground circuits, 1500m in length) Site 2/3: 2.3m (2x1000mm 2 Al 132kV underground circuits, 200m in length) Estimate time to implement 3-4 years (1 year consents negotiations, 3 years approval + construction) A geographical overview and photos of the sites are included in Appendix A2. This is the recommended option and will be investigated further in section 6 of this document. Option 7 - New Grid Supply Point at Coggeshall Option 7 proposes the creation of a new Grid Supply Point near Coggeshall, supplied from the 400kV circuits Bramford-Rayleigh. To fully implement this option, new 132kV circuits are required between Coggeshall GSP and the PCB overhead line, similar to option 5.2. Common works for option 7: a. Creation of a 400/132kV Grid Supply Point; b. Installation of a 400/132kV SGT by National Grid; c. Installation of 132kV feeder circuit breakers; Estimate cost for substation reinforcement works 21.3m Estimate time to implement 4 years (1 year approvals, 1 year enabling works, 2 year construction) Page 20 of 35

21 This option involves: d. Installation of two 132kV circuits between Coggeshall and Rushley Green: Option is for a overhead line with 175mm 2 conductors each capable of 99/123MVA along a 17.5km route (shortest route: 4 and 5); Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along a 18km route, 40% in carriage way; e. For the underground solution: 5 directional drills; f. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; g. Modification to the existing 132kV OHL near Bramford; Summary of Option 6 Route length 17.5km (minimum). Route initially assessed; Capacity available through connection: 198/246MVA (restricted by the existing 132kV OHL circuit); Wayleave consents are required; Environmental and ecological issues: o A substantial part of the route has been identified as known archaeological area; o Close proximity to Ancient woodland areas; o River crossings; Special Engineering Difficulties o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; The underground route is largely unexplored and will require route feasibility. Option kV Overhead line Estimate cost 16.5m Estimate total cost 37.8m Estimate time to implement 5-6 years (2-3 years consents negotiations, 2-3 years approval + construction) Option kV Underground cable Estimate cost 31.0m Estimate total cost 52.3m Estimate time to implement 5-6 years (2-3 years consents negotiations, 2-3 years approval + construction) Coggeshall GSP Figure 13. Simplified single line diagram for Option 5.1 and 5.2 (132kV connections shown) Page 21 of 35

22 This option has been discounted due to cost, high risk factor (archaeological and environmental), complex wayleave negotiations, long timescale and public awareness of new 132kV overhead lines. Option 8 - New Grid Supply Point at Earls Colne Option 8 proposes the creation of a new Grid Supply Point near Earls Colne, supplied from the 400kV circuits Bramford-Rayleigh. To fully implement option 7, new 132kV circuits are required between Earls Colne GSP and the PCB overhead line, similar to option 5.2. Common works for option 8: a. Creation of a 400/132kV Grid Supply Point; b. Installation of a 400/132kV SGT by National Grid; c. Installation of 132kV feeder circuit breakers; Estimate cost for substation reinforcement works 21.3m Estimate time to implement 4 years (1 year approvals, 1 year enabling works, 2 year construction) This option involves: d. Installation of two 132kV circuits between Coggeshall and Rushley Green: Option 8.1 is for a overhead line with 175mm 2 conductors each capable of 99/123MVA along a 10km route (shortest route: 4 and 5); Option 8.2 is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along a 10.5km route, 20% in carriage way; e. For the underground solution: 2 directional drills; f. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; g. Modification to the existing 132kV OHL near Bramford; Summary of Option 8 Route length 10km (minimum). Route initially assessed; Capacity available through connection: 198/246MVA (restricted by the existing 132kV OHL circuit); Wayleave consents are required; Environmental and ecological issues: o A substantial part of the route has been identified as known archaeological area; o Close proximity to Ancient woodland areas; o River crossing; Special Engineering Difficulties o River crossings: Colne; o Major roads: A1124; The underground route is largely unexplored and will require route feasibility. Option kV Overhead line Estimate cost 9.8m Estimate total cost 31.1m Estimate time to implement 5 years (2 years consents negotiations, 2-3 years approval + construction) Option kV Underground cable Estimate cost 22.9m Estimate total cost 44.2m Estimate time to implement 5 years (2 years consents negotiations, 2-3 years approval + construction) Page 22 of 35

23 Earls Colne GSP Figure 14. Simplified single line diagram for Option 5.1 and 5.2 (132kV connections shown) Page 23 of 35

24 4. STRATEGIC OPTIONS EVALUATION The options evaluation takes into account several criteria which consider relevant technical aspects, financial, deliverability, environmental and interactions with National Grid reinforcement programme. Each potential option has been assessed to ensure that it meets the need case to provide an alternative supply to the existing 132kV circuits between Twinstead Tee and Bramford and that the resultant distribution system is compliant with the various statutory and licence obligations. The implications on both the local and regional distribution system have been fully assessed and the impact on the current infrastructure development plan is understood. 4.1 Recommended Option It has been confirmed that Option 6 for a new Grid Supply Point in the proximity of Twinstead is the appropriate distribution network reinforcement that should be considered in the context of transferring the existing 132kV overhead line between Twinstead Tee and Burstall Bridge. The configuration of a new Grid Supply Point will depend on technical and operational considerations. Several configurations and running arrangements have been initially considered and are detailed in the table below along with the justification for non acceptance: Configuration of a new GSP Comments Outcome 1x SGT connected to a 132kV single circuit The existing 132kV circuit to Bramford provides 99/123MVA of capacity following a N-1 scenario. A connection to a single 132kV circuit would result in the loss of N-1 capacity and a reduction in network security. Reject 1xSGT Twinstead open 132kV CB at Thaxted 2xSGT open at Pelham CB 1xSGT open at Pelham 1xSGT connected to a 132kV double busbar in parallel to Pelham SGT 1xSGT connected to a 132kV double busbar in parallel to Pelham SGT 2xSGT connected to 2x 132kV CB at Twinstead 2xSGT connected to a 132kV double busbar Class D group requiring immediate recover of Belchamp winter MD-20MW= 60MW in 2010/11. NGET will need to secure the total demand immediately for a first circuit outage of the SGT or 400kV circuits. Without an automatic switching arrangement between Twinstead/Thaxted/Pelham it will not be possible to achieve the required response time through the 132kV network This option provides a limited use of the SGT s at Twinstead and no further benefit to variations 1, 2 and 3. Possible voltage step change issues. This option provides a limited use of the SGT s at Twinstead and no further benefit to variations 1, 2 and 3. Possible voltage step change issues. This option has been studied in detail This option has been studied in detail This option has been studied in detail This option has been studied in detail Reject Reject Reject Recommended Considered Considered Considered Page 24 of 35

25 kV Running Arrangement for Twinstead GSP 132kV network reconfiguration to Several 132kV running arrangement have been analysed for the Twinstead-Pelham-Wymondley Group which also provide further justification to the 132kV at Twinstead GSP. The preferred arrangement is for the 132kV busbar to run solid where fault level constraints permit and for all SGT to run in parallel. A typical double busbar arrangement is employed providing main and reserve busbars each with a bus section circuit breaker thereby providing discrete sections of the busbar to which a SGT is connected. The main and reserve busbar are coupled by means of a bus coupling circuit breaker. This configuration applies to both AIS and GIS designs. It has been determined that a 400/132kV SGT connected to a single section 132kV busbar with two 132kV feeder circuit breakers to the existing 132kV OHL is the preferred initial configuration for Twinstead GSP designed to accommodate future expansion to a 2xSGT and a double busbar 132kV with at least 4 feeder breakers as the DNO network evolves. The estimate total cost of the option is dependant on the location of the Grid Supply Point and is between 20.2 and 21.5m: Substation Site NG S/S element UKPN cct element Estimate total 3x132kV CB 2x132kV cct cost Site 1 - Buttlers Wood 17.9m 3.6m 21.5m Site 2 - Delvyns Lane 17.9m 2.3m 20.2m Site 3 - Colne Valley farm 17.9m 2.3m 20.2m 5. REFERENCES APPENDICES Reference Appendix A1 Appendix A2 Appendix A3 Description Eastern Power Networks Distribution area Twinstead GSP proposed locations Summary of Strategic Options DOCUMENTS Date October 2009 October 2009 June 2011 June 2011 Description Bramford to Twinstead connection Substation Sitting Study Bramford to Twinstead 400kV Overhead line project Strategic Optioneering Report Bramford to Twinstead Tee connection project Review of Strategic Options Report Bramford to Twinstead Tee Need case for the east Anglia region Page 25 of 35

26 APPENDIX A1: EASTERN POWER NETWORKS DISTRIBUTION AREA Page 26 of 35

27 APPENDIX A2: TWINSTEAD GSP PROPOSED LOCATIONS GSP Site 1 Butlers Wood and Waldegrave Wood Site 1 ~1.5km 400kV OHL crossing A131 View of Site 1 (Butler s wood left, Walgreave wood right) View of the 132kV from Site 1 Source (photos): National Grid. Page 27 of 35

28 GSP Site 2 Delvyns Lane Site 2 Sudbury Road heading to Castle Hedingham PCB 112 crossing site 2 400kV OHL north of site 2 Source (photos): National Grid. Page 28 of 35

29 GSP Site 3 - Colne Valley Farm Park Site 3 Entrance to Colne Valley Railway (Facing East) PCB kV Facing East (400kV on the left) Source (photos): National Grid. Page 29 of 35

30 Twinstead Diamond crossing 400kV/132kV PCB 88B 400kV/132kV Diamond Crossing (PCB 88A & PCB 88B) PCB 88A Source (photos): National Grid. Page 30 of 35

31 400kV Tee near Twinstead village 400kV Bramford/Rayleigh/Pelham (Twinstead Tee) Source (photos): National Grid. Page 31 of 35

32 APPENDIX A3: SUMMARY OF STRATEGIC OPTIONS Brief description Scope of Works Major Risks Cost / Time Result Option 1 - Do Nothing N/A N/A The current infrastructure is unable to permanently support the demand at Belchamp and Thaxted Grids without the backup offered by the 132kV circuits to Bramford. N/A Discount Option 2 - Replace 132kV circuits between Twinstead and Burstall Bridge Maintain the existing N-1 transfer a. Installation of two 132kV circuits, made up of single Environmental and ecological issues: Estimate total cost including reinforcement Rejected capacity between Pelham and Bramford core cables with a minimum size of 300mm² Al, each o Within the Stour Valley area. works at Bramford is 103m; by the replacement of an existing 26km capable of 107/126MVA, in ducted trefoil formation, o Dedham Vale area of outstanding natural beauty; of 132kV double circuit overhead line along a 26km route, partial in carriage way ; o Close proximity to ancient woodlands; Estimate time to implement 5-6 years with two 132kV underground circuits to b. 6 directional drill; o Identified archaeological areas; PCB5 near Bramford GSP. c. Construction of a 132kV terminal tower and Special Engineering Difficulties modifications to existing 132kV towers east of o River crossings: Stour, Brett and Belstead; Belchamp Tee; o Major roads: A131, A134, A1071; d. Modification to the existing 132kV OHL near o Network Rail: Sudbury to Marks Tey rural line; Bramford; Requires route feasibility study. This option would prompt upstream reinforcement at Bramford. Current estimate cost of reinforcement works at Bramford is 12.8m for reinforcing the 132kV circuit from Lawford to Bramford and 45m for 132kV switchgear replacement due to fault level. Option 3 - Extension of the 132kV PCB overhead line from Twinstead Maintain the existing N-1 transfer See 3.1 and 3.2 See 3.1 and 3.2 See 3.1 and 3.2 capacity from Pelham by the replacement of the existing 24km of 132kV double circuit overhead line with another 132kV double circuit. 3.1 Twinstead Lawford 132kV substation New 132kV circuits are required between Installation of two 132kV circuits along a 24km route. Environmental and ecological issues: Option kV Overhead line Rejected Twinstead and Lawford 132kV: Option is for an overhead line route with o Close proximity to Dedham Vale area of outstanding natural beauty; Estimate total cost including reinforcement Option kV Overhead line 175mm 2 conductors each capable of o Close proximity to Ancient woodland areas; works at Bramford is 80.5m; Option kV Underground cable 99/123MVA; o Identified archaeological areas; Estimate time to implement 6-7 years. Option is for an underground route with Special Engineering Difficulties single core cables with a minimum size of o River crossings: Colne; Option kV Underground cable 300mm² Al, each capable of 107/126MVA, in o Major roads: A12, A134, A137; Estimate total cost including reinforcement ducted trefoil formation, 30% in carriage way; o Network rail: Norwich London Liverpool street main line and Sudbury works at Bramford is 98m; a. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; b. Modification to the existing 132kV OHL near Bramford; Marks Tey rural line. This option would prompt upstream reinforcement at Bramford. Current estimate cost of reinforcement works at Bramford is 12.8m for reinforcing the 132kV circuit from Lawford to Bramford and 45m for 132kV switchgear replacement due to fault level. Estimate time to implement 5-6 years. Page 32 of 35

33 3.2 Twinstead Abberton Grid (OHL or UG) New 132kV circuits are required between a. Installation of two 132kV circuits along a 22km Environmental and ecological issues: Option kV Overhead line Twinstead and Abberton 132kV: route. o Close proximity to the Dedham vale area of outstanding natural beauty; Estimate total cost including reinforcement Option kV Overhead line Option is for an overhead line route with o Close proximity to Ancient woodland areas; to Bramford is 79m; Option kV Underground cable 175mm 2 conductors each capable of o Identified archaeological areas; Estimate total cost including reinforcement 99/123MVA; Special Engineering Difficulties works to Rayleigh is 75m; Option is for an underground route with o Crossing of the Bramford Rayleigh Pelham 400kV circuit; Estimate time to implement 6-7 years. single core cables with a minimum size of o River crossings: Colne and Roman; 300mm² Al, each capable of 107/126MVA, in o Major roads: A12, A1124 A120, A1071; Option kV Underground cable ducted trefoil formation, 20% in carriage way; o Network rail: London Liverpool street main line and Sudbury Marks Tey Estimate total cost including reinforcement b. Construction of a 132kV terminal tower and rural line. works at Bramford is 96m; modifications to existing 132kV towers east of A detailed assessment is required to identify reinforcement of the 132kV circuits Estimate total cost including 132kV Belchamp Tee; and increased SGT capacity on the Bramford/Rayleigh group depending on the reinforcement works to Rayleigh is 92.5m; c. Modification to the existing 132kV OHL near location of the 132kV injection at Colchester. Estimate time to implement 5-6 years. Bramford; Estimate cost of reinforcement works at Bramford is 12.8m for reinforcing the 132kV circuit from Lawford to Bramford and 45m for 132kV switchgear replacement due to fault level. Estimate costs for reinforcement of the 132kV circuits to Rayleigh is 50m. Option 4-33kV Network Reinforcement The loss of the 132kV circuits to Bramford See 4.1 and 4.2 See 4.1 and 4.2 See 4.1 and 4.2 GSP results in a P2/6 non compliance due to insufficient backup available from the 33kV network to support the demand of Belchamp and Thaxted Grid. 4.1 Resolve 33kV circuit constraints This option would involve installing Reinforce of 33kV circuits. See document. Technical constraints (voltage limitations), inability to permanently supply Haverhill, Estimate total cost of reinforcement at 33kV remote switching in the network and Sudbury and Saffron Walden for a N-2 on the 132kV OHL and offers limited capacity is 9.4m. replacing the limiting overhead line increase. circuits Rejected Rejected 4.2 Increase 33kV interconnection 33kV interconnection from Belchamp and Thaxted can be enhanced by constructing new 33kV interconnectors There are several projects within UKPN investment plan to provide additional circuits and improve the resilience of the network in the area: The increase in interconnection would resolve the immediate issues but won t provide sufficient capacity to cater for the developments expected in the area Estimate total cost of reinforcement at 33kV is 20m. Rejected Option 5 - Reinforce Braintree GSP and install new 132kV circuits to Rushley Green Maintain the existing N-1 transfer Common works for option 5: See 5.1 and 5.2 Estimate cost for substation reinforcement capacity between Pelham and Bramford a. Modifications to the 400kV arrangement at Braintree works 32m by the replacement of the existing 26km by National Grid; Estimate time to implement 4 years of 132kV double circuit overhead line b. Installation of a 3 rd 400/132kV SGT by National Grid; with two 132kV circuits to Braintree GSP c. Installation of two 132kV circuit breakers and associated equipment; Page 33 of 35

34 kV Braintree Rushley Green (OHL or UG) New 132kV circuits are required between Braintree GSP and the PCB overhead line. d. Installation of two 132kV circuits between Braintree and the 132kV PCB OHL: Option is for a overhead line with 175mm 2 conductors capable of 99/123MVA along a 18km route; Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along a 17km route, 50% in carriage way; e. For the underground solution: 5 directional drills; f. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; g. Modification to the existing 132kV OHL near Bramford; Environmental and ecological issues: o Close proximity to Ancient woodland areas; o Identified archaeological areas; Special Engineering Difficulties o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; Reinforcement at Braintree has been identified following the connection to the 132kV PCB circuit. Option kV Overhead line Estimate total cost including reinforcement works at Braintree is 49m Estimate time to implement 5-6 years Option kV Underground cable Estimate total cost including reinforcement works at Braintree is 62.4m Estimate time to implement 5-6 years Rejected kV OHL Braintree Abberton teed off to Twinstead (OHL or UG) d. Installation of two 132kV circuits between Coggeshall and Rushley Green: New 132kV overhead line circuits are required between Coggeshall and the PCB overhead line Option 6 - New Grid Supply Point at Twinstead Creation of a new Grid Supply Point near Twinstead, adjacent to the 400kV circuits Bramford-Pelham and in close proximity with the Thaxted to Bramford 132kV circuits Option is for a overhead line with 175mm 2 conductors capable of 99/123MVA on a 17.5km route; Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along an 18km route, 40% in carriage way; e. For the underground solution: 5 directional drills; f. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; g. Modification to the existing 132kV OHL near Bramford; Environmental and ecological issues: Option kV Overhead line o Close proximity to Ancient woodland areas; Estimate total cost including reinforcement o Identified archaeological areas; works at Braintree is 46.5m Special Engineering Difficulties Estimate time to implement 5-6 years o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; Option kV Underground Reinforcement at Braintree has been identified following the connection to the Estimate total cost including reinforcement 132kV PCB circuit. works at Braintree is 63m Estimate time to implement 5-6 years a. Creation of a 400/132kV Grid Supply Point; Environmental and ecological issues: See Report for details. Several running Recomm b. Installation of 400/132kV SGT by National Grid. o Close proximity to Ancient woodland areas; arrangements have been proposed and the end Further information on 6.1; Special Engineering Difficulties recommendation is for a single 400/132kV o No major engineering difficulties indentified. SGT connected to a single busbar to 132kV feeder circuit breakers connected to the existing OHL. c. Installation of 132kV switchgear. Further information on 6.1; d. Installation of two 132kV underground circuits between the substation and the 132kV circuits; e. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; f. Modification to the existing 132kV OHL near Bramford; Estimate cost is dependant on the location of the Grid Supply Point as per the table below: Site 1 - Buttlers Wood 21.5m Site 2 - Delvyns Lane 20.2m Site 3 - Colne Valley farm 20.2m Rejected Page 34 of 35

35 Option 7 - New Grid Supply Point at Coggeshall Creation of a new Grid Supply Point near Coggeshall, supplied from the 400kV circuits Bramford-Rayleigh. Option kV Overhead line Option kV Underground cable Option 8 - New Grid Supply Point at Earls Colne Creation of a new Grid Supply Point near Earls Colne, supplied from the 400kV circuits Bramford-Rayleigh. a. Creation of a 400/132kV Grid Supply Point; b. Installation of a 400/132kV SGT by National Grid; c. Installation of 132kV feeder circuit breakers; d. Installation of two 132kV circuits between Coggeshall and Rushley Green: Option is for a overhead line with 175mm 2 conductors each capable of 99/123MVA along a 17.5km route (shortest route: 4 and 5); Option is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along a 18km route, 40% in carriage way; e. For the underground solution: 5 directional drills; f. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; g. Modification to the existing 132kV OHL near Bramford; a. Creation of a 400/132kV Grid Supply Point; b. Installation of a 400/132kV SGT by National Grid; c. Installation of 132kV feeder circuit breakers; d. Installation of two 132kV circuits between Coggeshall and Rushley Green: Option 8.1 is for a overhead line with 175mm 2 conductors each capable of 99/123MVA along a 10km route (shortest route: 4 and 5); Option 8.2 is for an underground route with single core cables with a minimum size of 300mm² Al, each capable of 107/126MVA, in ducted trefoil formation along a 10.5km route, 20% in carriage way; e. For the underground solution: 2 directional drills; f. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee; g. Modification to the existing 132kV OHL near Bramford; Environmental and ecological issues: o A substantial part of the route has been identified as known archaeological area; o Close proximity to Ancient woodland areas; o River crossings; Special Engineering Difficulties o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; The underground route is largely unexplored and will require route feasibility. Environmental and ecological issues: o A substantial part of the route has been identified as known archaeological area; o Close proximity to Ancient woodland areas; o River crossing; Special Engineering Difficulties o River crossings: Colne; o Major roads: A1124; The underground route is largely unexplored and will require route feasibility. Option kV Overhead line Estimate total cost 37.8m Estimate time to implement 5-6 years Option kV Underground cable Estimate total cost 52.3m Estimate time to implement 5-6 years Option kV Overhead line Estimate total cost 31.1m Estimate time to implement 5 years Option kV Underground cable Estimate total cost 44.2mx Estimate time to implement 5 years Rejected Rejected Page 35 of 35