132kV Network Reconfiguration

132kV network reconfiguration to accommodate wider systems works

July 2012

132kV network reconfiguration to

accommodate wider systems works CONTENTS

1. Executive Summary......................................................................................................................................4

2. UK Power Networks Business Case ..............................................................................................................5

2.1 Existing network infrastructure.................................................................................................................5

2.2 Pelham & Wymondley Group – Overall assessment ..................................................................................6

2.3 P2/6 compliance – Transfer of Belchamp Grid to Bramford.......................................................................8

2.4 P2/6 compliance – Thaxted & Belchamp Grid...........................................................................................9

3. 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...................................................................................................22

4. Strategic Options evaluation .....................................................................................................................24

4.1 Recommended Option ...........................................................................................................................24

4.2 132kV Running Arrangement for Twinstead GSP .....................................................................................25

5. References.................................................................................................................................................25

APPENDIX A1: Eastern Power Networks Distribution area .................................................................................26

APPENDIX A2: Twinstead GSP – proposed locations ........................................................................................27

APPENDIX A3: Summary of strategic options....................................................................................................32

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accommodate wider systems works Glossary of Terms

ACS Average Cold Spell

ACSR Aluminum Conductor Steel Reinforced

Al Aluminum

BR British Rail

CB Circuit Breaker

CI Customer Interruptions

CML Customer Minutes Lost

Cu Copper

DG Distributed Generation

DNO Distribution Network Operator

DPCR Distribution Price Control Review

EHV Extra High Voltage (132 kV)

EPN Eastern Power Networks

FCO First Circuit Outage

GSP Grid Supply Point

HV High Voltage (>11 kV)

kV Kilo Volt: 1000 V

LV Low Voltage

MVA Mega Volt Ampere

MW Mega Watt

NAMP Network Asset Management Plan

NG National Grid

NOP Normally Open Point

OF Oil Filled

OFGEM Office of Gas and Electricity Markets

OHL Overhead Line

PLE Planning Load Estimate

POC Point of Connection

RDP Regional Development Plan

RIIO Revenue = Incentives + Innovation + Outputs

RMS Root Mean Square

SC Single Core

SCADA Supervisory Control and Data Acquisition

SCO Second Circuit Outage

SCP Single Core Poly

SGT Super Grid Transformer

SLD Single Line Diagram

St Steel

UKPN UK Power Networks

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accommodate wider systems works

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.

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2. UK POWER NETWORKS BUSINESS CASE

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.

<PCB

211

>

770/

843

A17

6/19

3M

VA

<PCB

27

3>

<PCB

32

3>

<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 175mm2 ACSR conductors (PSB-PSA) with a 2.2km section of 500mm2 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

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accommodate wider systems works 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 175mm2 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 400mm2, 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 175mm2 and is connected to two Bramford circuits at tower PCB5:

1. Circuit number 1 (PCB No1) is connected to the 300mm2 Cliff Quay 4 OHL; 2. Circuit number 2 (PCB No2) is connected to the 300mm2 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).

Pelham and Wymondley

0.0

100.0

200.0

300.0

400.0

500.0

600.0

700.0

05/06 07/08 09/10 11/12 13/14 15/16 17/18 19/20 21/22 23/24 25/26 Year

MW

Actual Predicted

Figure 2. Pelham & Wymondley - Winter Maximum Demand (Actual and Predicted)

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accommodate wider systems works The minimum demand to be met in this group under outage conditions is detailed in the P2/6 table below

Circuit outage Minimum demand to be met for a class E (between 300MW and 1500MW)

First circuit outage Immediately: Group demand ► 492.6MW

Second circuit outage 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

Pelham 132kV SGT1 or SGT 2 out

Wymondley 132kV SGT1 or SGT 2 out

Circuit number 1 fault Pelham – Wymondley 132kV circuit

Circuit number 2 fault


First Circuit Outage (FCO)

Winter maximum demand

Pelham – Thaxted 132kV circuit


Pelham 132kV SGT1 on outage and SGT 2 on fault

Wymondley 132kV SGT1 on outage and SGT 2 on fault

Pelham – Wymondley 132kV circuit Loss of circuit no.1 and no.2

Second Circuit Outage (SCO)

Summer maximum demand

Pelham – Thaxted 132kV circuit 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 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.

3 phase and earth fault at Pelham 132kV above switchgear rating for both peak make and RMS break.

Load flow – Normal running

No issues of note 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

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FCO Winter 2017/18 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).

P2/6 assessment

SCO Summer 2016

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

BR UGLEY

BELCHAMP132/33kV S/S

PELHAM GSP

400/132kV S/S2x240MVA SGT

25kVBISHOPS

STORTFORD132/33kV S/S

MELBOURNE132/33kV S/S

NO.1

NO.2

STEVENAGE132/33kV S/S

WYMONDLEY GSP


745/925 A172/211 MVA

433/539 A99/123 MVA

THAXTED132/33kV S/S

WYMONDLEYGRID

132/33kV S/S

433/539 A99/123 MVA

799/875 A181/199 MVA

LETCHWORTH132/33kV S/S

HV Bows Off

269 A

290 A

354 A

447 A

751 A

679 A

112 A 123 A

517 A 153 A

156 A

NO.1

NO.2

Figure 3. P2/6 assessment for SCO in Summer 2016

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 400mm2 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.

BR UGLEY

BELCHAMP132/33kV S/S

PELHAM GSP


25kVBISHOPS

STORTFORD132/33kV S/S

MELBOURNE132/33kV S/S

NO.1

NO.2

STEVENAGE132/33kV S/S

WYMONDLEY GSP


745/925 A172/211 MVA

433/539 A99/123 MVA

THAXTED132/33kV S/S

WYMONDLEYGRID

132/33kV S/S

433/539 A99/123 MVA

799/875 A181/199 MVA

LETCHWORTH132/33kV S/S

HV Bows Off

921 A337 A

265 A

540 A

112 A 123 A

465 A

NO.1

NO.2

227 A

Figure 4. N-1 scenario for winter 2021/22 demand (estimate)


accommodate wider systems works 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 (20th 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 Minimum demand to be met for a class D (between 60MW and 300MW)

First circuit outage 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.

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accommodate wider systems works 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 SUDBURY WIXDE

PUMPING

132kV N-2

Figure 5. Effect of a 132kV N-2 scenario in Belchamp and Thaxted areas

(Simplified to show the affected area)

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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

Option 1 Do Nothing

Option 2 Replace 132kV circuits between Twinstead and Burstall Bridge

Option 3 Extension of the 132kV PCB overhead line from Twinstead

3.1.1 Twinstead – Lawford 132kV substation (New 132kV OHL circuits) 3.1.1 Twinstead – Lawford 132kV substation (New 132KV UG circuits)

3.2.1 Twinstead – Abberton Grid (New 132kV OHL circuits) 3.2.2 Twinstead – Abberton Grid (New 132KV UG circuits)

Option 4 33kV Network Reinforcement

4.1 Resolve 33kV circuit constraints

4.2 Increase 33kV interconnection

Option 5 Reinforce Braintree GSP and install new 132kV circuits to Rushley Green

5.1.1 132kV Braintree – Rushley Green (New 132kV OHL circuits) 5.1.2 132kV Braintree – Rushley Green (New 132KV UG circuits)

5.2.1 132kV Braintree – Abberton teed off to Twinstead (New 132kV OHL circuits) 5.2.1 132kV Braintree – Abberton teed off to Twinstead (New 132KV UG circuits)

Option 6 New Grid Supply Point at Twinstead

Option 7 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)

Option 8 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.

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accommodate wider systems works 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.

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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 5th 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 3.1.1 is for an overhead line route with 175mm2 conductors each capable of 99/123MVA; Option 3.1.2 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, 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 3.1.1 and 3.1.2

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 3.1.1 – 132kV 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 3.1.2 – 132kV 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)

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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 3.2.1 is for an overhead line route with 175mm2 conductors each capable of 99/123MVA; Option 3.2.2 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, 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 3.1.1 and 3.1.2

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 3.2.1 – 132kV 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 3.2.2 – 132kV Underground cable, Estimate cost £38.5m

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accommodate wider systems works 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 146-224): 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 99-116): 0.2Cu rated at 425/530A;

From Stowmarket Grid: 33kV OHL Stowmarket to Hadleigh (pole 1-115, pole 116-130 and pole 131-165): 0.1Cu rated at 269/336A;

From Braintree Grid: 33kV OHL Braintree Grid to West Braintree (pole 106-149): 0.1Cu rated at 269/336A;

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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 300mm2 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.

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accommodate wider systems works To provide capacity and enable the permanent transfer of Belchamp Grid, to resolve the predicted P2/6 non-compliance, a 3rd 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 3rd 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 5.1.1 is for a overhead line with 175mm2 conductors each capable of 99/123MVA along a 18km route; Option 5.1.2 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 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 5.1.1 – 132kV 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 5.1.2 – 132kV 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)

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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 5.2.1 is for a overhead line with 175mm2 conductors each capable of 99/123MVA on a 17.5km route; Option 5.2.2 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 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;


Reinforcement at Braintree has been identified. Option 5.2.1 – 132kV 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)

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accommodate wider systems works Option 5.2.2 – 132kV 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)

New

Coggeshall Grid

Braintree GSP

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.

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1 Twinstead GSP

2 3

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 (2x1000mm2 Al 132kV underground circuits, 1500m in length) Site 2/3: £2.3m (2x1000mm2 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)

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accommodate wider systems works This option involves:

d. Installation of two 132kV circuits between Coggeshall and Rushley Green: Option 5.2.1 is for a overhead line with 175mm2 conductors each capable of 99/123MVA along a 17.5km route (shortest route: 4 and 5); Option 5.2.2 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 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;


The underground route is largely unexplored and will require route feasibility. Option 7.1 – 132kV 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 7.2 – 132kV 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


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accommodate wider systems works 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 175mm2 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 8.1 – 132kV 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 8.2 – 132kV 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)

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Earls Colne GSP


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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

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

Reject

2xSGT open at Pelham CB 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.

Reject

1xSGT open at Pelham 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.

Reject

1xSGT connected to a 132kV double busbar in parallel to Pelham SGT

This option has been studied in detail Recommended

1xSGT connected to a 132kV double busbar in parallel to Pelham SGT

This option has been studied in detail Considered

2xSGT connected to 2x 132kV CB at Twinstead


2xSGT connected to a 132kV double busbar


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4.2 132kV Running Arrangement for Twinstead GSP 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:

NG S/S element UKPN cct element Substation Site

3x132kV CB 2x132kV cct

Estimate total 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 Description

Appendix A1 Eastern Power Networks Distribution area

Appendix A2 Twinstead GSP – proposed locations

Appendix A3 Summary of Strategic Options

DOCUMENTS Date Description

October 2009 Bramford to Twinstead connection – Substation Sitting Study

October 2009 Bramford to Twinstead 400kV Overhead line project – Strategic Optioneering Report

June 2011 Bramford to Twinstead Tee connection project – Review of Strategic Options Report

June 2011 Bramford to Twinstead Tee – Need case for the east Anglia region


APPENDIX A1: EASTERN POWER NETWORKS DISTRIBUTION AREA

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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.

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GSP Site 2 – Delvyns Lane

Site 2

Sudbury Road heading to Castle Hedingham PCB 112 crossing site 2 400kV OHL north of site 2


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GSP Site 3 - Colne Valley Farm Park

Site 3

Entrance to Colne Valley Railway (Facing East) PCB123 132kV Facing East (400kV on the left)


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Twinstead Diamond crossing 400kV/132kV

PCB 88B 400kV/132kV Diamond Crossing (PCB 88A & PCB 88B) PCB 88A


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400kV Tee near Twinstead village

400kV Bramford/Rayleigh/Pelham (Twinstead Tee)



APPENDIX A3: SUMMARY OF STRATEGIC OPTIONS

Brief description Scope of Works Major Risks Cost / Time Result

Option 1 - Do Nothing

Discount 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

Option 2 - Replace 132kV circuits between Twinstead and Burstall Bridge

Environmental and ecological issues: 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 ;

Rejected 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.

Estimate total cost including reinforcement works at Bramford is £103m; o Within the Stour Valley area.

o Dedham Vale area of outstanding natural beauty; Estimate time to implement 5-6 years o Close proximity to ancient woodlands;

o Identified archaeological areas; b. 6 directional drill; Special Engineering Difficulties c. Construction of a 132kV terminal tower and

modifications to existing 132kV towers east of Belchamp Tee;

o River crossings: Stour, Brett and Belstead; o Major roads: A131, A134, A1071; o Network Rail: Sudbury to Marks Tey rural line; d. Modification to the existing 132kV OHL near

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 capacity from Pelham by the replacement of the existing 24km of 132kV double circuit overhead line with another 132kV double circuit.

See 3.1 and 3.2 See 3.1 and 3.2 See 3.1 and 3.2

3.1 Twinstead – Lawford 132kV substation

Environmental and ecological issues: Rejected New 132kV circuits are required between Twinstead and Lawford 132kV: Option 3.1.1 – 132kV Overhead line Option 3.1.2 – 132kV Underground cable

Installation of two 132kV circuits along a 24km route. Option 3.1.1 – 132kV Overhead line Estimate total cost including reinforcement works at Bramford is £80.5m;

o Close proximity to Dedham Vale area of outstanding natural beauty; Option 3.1.1 is for an overhead line route with 175mm2 conductors each capable of 99/123MVA;

o Close proximity to Ancient woodland areas; o Identified archaeological areas; Estimate time to implement 6-7 years.

Option 3.1.2 – 132kV Underground cable Estimate total cost including reinforcement works at Bramford is £98m;

Special Engineering Difficulties Option 3.1.2 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, 30% in carriage way;

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. a. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee;

Estimate time to implement 5-6 years. 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.

b. Modification to the existing 132kV OHL near Bramford;

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3.2 Twinstead – Abberton Grid (OHL or UG)

Environmental and ecological issues: a. Installation of two 132kV circuits along a 22km route.

Rejected New 132kV circuits are required between Twinstead and Abberton 132kV: Option 3.2.1 – 132kV Overhead line Option 3.2.2 – 132kV Underground cable

Option 3.2.1 – 132kV Overhead line Estimate total cost including reinforcement to Bramford is £79m;

o Close proximity to the Dedham vale area of outstanding natural beauty; o Close proximity to Ancient woodland areas; Option 3.2.1 is for an overhead line route with

175mm2 conductors each capable of 99/123MVA;

o Identified archaeological areas; Estimate total cost including reinforcement works to Rayleigh is £75m; Special Engineering Difficulties

o Crossing of the Bramford – Rayleigh – Pelham 400kV circuit; Option 3.2.2 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, 20% in carriage way;

Estimate time to implement 6-7 years. Option 3.2.2 – 132kV Underground cable Estimate total cost including reinforcement works at Bramford is £96m;

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. b. Construction of a 132kV terminal tower and modifications to existing 132kV towers east of Belchamp Tee;

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 total cost including 132kV reinforcement works to Rayleigh is £92.5m;

c. Modification to the existing 132kV OHL near Bramford;

Estimate time to implement 5-6 years. 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 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.

See 4.1 and 4.2 See 4.1 and 4.2 See 4.1 and 4.2

4.1 Resolve 33kV circuit constraints

Rejected This option would involve installing remote switching in the network and replacing the limiting overhead line circuits

Reinforce of 33kV circuits. See document.

Technical constraints (voltage limitations), inability to permanently supply Haverhill, Sudbury and Saffron Walden for a N-2 on the 132kV OHL and offers limited capacity increase.

Estimate total cost of reinforcement at 33kV is £9.4m.

4.2 Increase 33kV interconnection

Rejected 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.

Option 5 - Reinforce Braintree GSP and install new 132kV circuits to Rushley Green

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

Common works for option 5: See 5.1 and 5.2 Estimate cost for substation reinforcement works £32m a. Modifications to the 400kV arrangement at Braintree

by National Grid; Estimate time to implement 4 years

b. Installation of a 3rd 400/132kV SGT by National Grid; c. Installation of two 132kV circuit breakers and

associated equipment;

Page 33 of 35


5.1 132kV Braintree – Rushley Green (OHL or UG)

Environmental and ecological issues: d. Installation of two 132kV circuits between Braintree and the 132kV PCB OHL:

Rejected New 132kV circuits are required between Braintree GSP and the PCB overhead line.

Option 5.1.1 – 132kV Overhead line Estimate total cost including reinforcement works at Braintree is £49m Estimate time to implement 5-6 years Option 5.2.2 – 132kV Underground cable Estimate total cost including reinforcement works at Braintree is £62.4m Estimate time to implement 5-6 years

o Close proximity to Ancient woodland areas; o Identified archaeological areas; Option 5.1.1 is for a overhead line with 175mm2

conductors capable of 99/123MVA along a 18km route;

Special Engineering Difficulties o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; Option 5.1.2 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 17km route, 50% in carriage way;

Reinforcement at Braintree has been identified following the connection to the 132kV PCB circuit.

e. For the underground solution: 5 directional drills; f. Construction of a 132kV terminal tower and


g. Modification to the existing 132kV OHL near Bramford;

5.2 132kV OHL Braintree – Abberton teed off to Twinstead (OHL or UG)

Environmental and ecological issues: d. Installation of two 132kV circuits between Coggeshall and Rushley Green:

Rejected New 132kV overhead line circuits are required between Coggeshall and the PCB overhead line

Option 5.2.1 – 132kV Overhead line o Close proximity to Ancient woodland areas; Estimate total cost including reinforcement

works at Braintree is £46.5m o Identified archaeological areas; Option 5.2.1 is for a overhead line with 175mm2 conductors capable of 99/123MVA on a 17.5km route;

Special Engineering Difficulties Estimate time to implement 5-6 years o River crossings: Blackwater and Colne; o Major roads: A131, A120, A1071; Option 5.2.2 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 an 18km route, 40% in carriage way;

Option 5.2.2 – 132kV Underground Estimate total cost including reinforcement works at Braintree is £63m

Reinforcement at Braintree has been identified following the connection to the 132kV PCB circuit.

Estimate time to implement 5-6 years




Option 6 - New Grid Supply Point at Twinstead

Environmental and ecological issues: a. Creation of a 400/132kV Grid Supply Point; Recommend

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

See Report for details. Several running arrangements have been proposed and the recommendation is for a single 400/132kV SGT connected to a single busbar to 132kV feeder circuit breakers connected to the existing OHL.

o Close proximity to Ancient woodland areas; b. Installation of 400/132kV SGT by National Grid. Further information on 6.1; Special Engineering Difficulties

o No major engineering difficulties indentified. 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;

Estimate cost is dependant on the location of the Grid Supply Point as per the table below:

f. Modification to the existing 132kV OHL near Bramford;

Site 1 - Buttlers Wood £21.5m Site 2 - Delvyns Lane £20.2m Site 3 - Colne Valley farm £20.2m

Page 34 of 35


Page 35 of 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 7.1 – 132kV Overhead line Option 7.2 – 132kV Underground cable

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 7.2.1 is for a overhead line with 175mm2 conductors each capable of 99/123MVA along a 17.5km route (shortest route: 4 and 5); Option 7.2.2 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 18km route, 40% in carriage way;




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;


The underground route is largely unexplored and will require route feasibility.

Option 7.1 – 132kV Overhead line Estimate total cost £37.8m Estimate time to implement 5-6 years Option 7.2 – 132kV Underground cable Estimate total cost £52.3m Estimate time to implement 5-6 years

Rejected

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 8.1 is for a overhead line with 175mm2 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;




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 8.1 – 132kV Overhead line Estimate total cost £31.1m Estimate time to implement 5 years Option 8.2 – 132kV Underground cable Estimate total cost £44.2mx Estimate time to implement 5 years

Rejected

Date post:	25-Dec-2015
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132kV Network Reconfiguration

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