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 Page 2 of 35 132kV network reconfiguration to 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 Page 3 of 35 132kV network reconfiguration to 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. Page 4 of 35 132kV network reconfiguration to accommodate wider systems works 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