SPN High Value Project PO Route. RIIO-ED1 Investment Justification Reinforcement for PO Route Network: SPN

Transcription

1 SPN High Value Project PO Route RIIO-ED1 Investment Justification Reinforcement for PO Route Network: SPN

2 Document History Version Date Details Originator V0.1 20/06/2013 Initial version Chris Winch V0.2 23/06/2013 Updates and clarifications Mark Fitch V0.3 24/06/2013 Further clarifications Mark Fitch V1.0 24/06/2013 Draft for review Tendai Matiringe V1.1 24/06/2013 Minor revisions to options description Chris Winch 1

3 EXECUTIVE SUMMARY The preferred approach is to create a new Grid Supply Point to supply Lewes Grid before the single circuit PO route is dismantled. This requires National Grid to construct and commission a new GSP at Horsted Green, installing two 400/132kV transformers and two 132kV circuit breakers (estimated between 14.7 to 16.3M). Lewes Grid would be connected to this new GSP via two new 132kV underground circuits from Horsted Green to Lewes Grid with outdoor 132kV sealing ends at Lewes Grid and at the new GSP. In addition one new 132kV circuit breaker would be added at Lewes Grid on the existing PLB line from Fishersgate to connect in the additional circuit. This allows the dismantling of towers PO86 to PO16 (a rural section under threat from wayleave termination) that run through the National Park. The estimate total cost of the project is 37.2M ( 31.4M in ED1), the lowest cost of all the estimated options. The main drivers for the preferred approach are: o Avoid the need to asset replace the existing single circuit overhead line between Eastbourne and Lewes (Route PO) o Maintain P2/6 Licence compliance to the Lewes and Newhaven group o Avoid the significant risk to land rights to maintain the existing PO Route as a single circuit and the resulting impact on security of supply if rights are terminated o Avoid the need to negotiate a change to the existing rights to allow the route to be rebuilt as double circuit to support load growth The major benefits of preferred approach: o Removal of an overhead line route from a National Park/ area of outstanding natural beauty a key issue for our stakeholders o Reinforcement supports future load growth in the Lewes/Newhaven demand group o Deferral of reinforcement at the adjacent Bolney and Ninfield GSPs BACKGROUND The Lewes - Eastbourne 132kV single circuit tower line is 22 kilometres in length comprising 86 towers and is routed parallel to the south coast. Condition surveys have confirmed the need to asset replace the overhead line due to deteriorating condition. The route traverses the South Downs National Park and works are subject to intense scrutiny to minimise the visual impact of the rebuilt line or its replacement on Areas of Outstanding Natural Beauty (AONBs) through which it passes. This is coupled with escalating initiatives by lobby groups to protect Special Sites of Scientific Interest (SSSI s). These environmental pressures represented a threat to the security of the route and any replacement. 2

4 Any rebuilding, even partial tower rebuilds in the National Park would require permission from the Local Authorities, the Department of Energy and Climate Change (DECC), National Park Land and the Infrastructure Planning Commission, and it is uncertain if this will be granted. The rebuilding of the line was part of our plans in DPCR5. This was for the line to be rebuilt as a double circuit tower line. At that time the group demand was growing, but somewhat below the limit for group demand supplied by the existing two circuits. The works on the circuit could not go ahead because of a number of existing wayleave terminations affecting the rural section. These include two claims in span PO39-PO40, another two claims in PO39-PO38 and one in section PO37-PO36. There is also a threat of termination in span PO42-PO43 although this claim is presently not being pursued by the landowner on the understanding that UK Power Networks is intending to remove the overhead line in the near future. Action has been taken to maintain the integrity of the route while the solution to the wayleave issues has been progressed. Refurbishment work completed in August 2010 replaced rusting tower members and has prolonged the service life by a period of approximately 10 years to 2021, subject to continuous condition monitoring. Further refurbishment works on the route is being undertaken to main the integrity of the line during DPCR5. Description /2012 /2013 /2014 /2015 PO Route Tower Refurbishment (PO16 to 86) The loss of rights to maintain the PO route is a high risk, with landowners anticipating the dismantlement of the line and wayleaves are unlikely to be renewed. The loss of this route would bring an immediate security of supply issues for the Lewes-Newhaven demand group. While we take action to mitigate this risk we are also considering how we fulfil demand growth into the future for the Lewes and Newhaven demand group. Rebuilding or replacing the route in its current single-circuit form would be ineffective in meeting future growth in demand. Further works would be required to support the Lewes-Newhaven demand group to provide security of supply in the future to maintain compliance with Engineering Recommendation P2/6 with the current transfer capability, this may be in ED2 or beyond. The peak winter group demand is 103MW which is forecast to increase to 107W by 2023 (Table 1 refers). Table 1: Extract from CV102 Substation Primary Voltage Secondary Voltage Substation firm capacity under single circuit outage conditions Assessed contribution towards security supply from DG adjustment "Significant" measurable embedded generation adjustment to maximum demand Max demand (MVA) Substation (kv) (kv) MVA MVA (+) MVA (+/-) 2011/ /23 Lewes Grid Newhaven Grid Total

5 The demand group supplied from Lewes 132kV substation is connected by two single circuit overhead line connections one from Eastbourne (Route PO) and one from Southern Cross (Route PLB). Newhaven demand is connected via two 132kV transformer feeders onward connected from Lewes. The Southern Cross to Lewes PLB route, also crosses that National Park, is of single circuit construction and we would be similarly unlikely to gain permissions to make this a double circuit route. The geographical and network configurations are shown in the Figures below. Figure 1: Geographical Configuration Little Horsted Double circuit 400kV OHL PLB ROUTE: Single circuit 132kV OHL PO ROUTE: Single circuit 132kV OHL Mile Oak Arlington South Downs National Park Note: 400kV routes in red, 132kV routes in green and 33kV routes in pink. Indication of National Park boundaries in light blue shading. The exact boundaries are shown below. Figure 2: National Park Boundaries 4

6 Figure 3: Lewes Newhaven network configuration Figure 4: Route PO The options considered seek to remove the risk of the loss of the PO route and to accommodate the future load growth and security of supply requirements for the Lewes- Newhaven demand group.. SUMMARY OF THE ALTERNATIVES CONSIDERED Previously considered option The rebuilding of the line (estimated at 17.1M) was part of our plans in DPCR5. This was for the line to be rebuilt as a double circuit tower line. The works on the circuit could not go ahead because of a number of existing wayleave terminations affecting the rural section. Investigations to utilise insulated cross-arm new technology to lower the line profile but, based on recent experience, renegotiating permissions to rebuild this route it is considered to have a low probability of success. Reinforcement considerations has increased the importance of finding a solution to securing future supplies to this demand group and four options have been considered: Option 1 Do Nothing. Rejected due to deteriorating condition of the overhead line and requirement to reinforce the Lewes / Newhaven group Option 2 Phased replacement of the single circuit tower route PO86 to PO16 with two underground cable circuits from Lewes Grid to tower PXB6 through the following stages: 1. Replace top half of the towers and cable the PO circuit in Polegate in period

7 2. Uprate 9.6km of 33kV cable between Moulsecoomb, Rottingdean and Newhaven in to enable Seaford to be recovered under N-2 conditions 3. Replace 132kV circuit from Mile Oak to Southern Cross in 2028 to increase the N-1 firm capacity of the group 4. Complete the replacement of the route from Lewes Grid to tower PXB6 in period with a double underground cable circuit to maintain N-2 compliance Estimated cost M Access permissions are expected to introduce significant delivery risk due to disruption to landowners. Work on the existing towers is likely to accelerate the terminations on the existing Wayleaves. Option 3 Replace part of the PO single circuit route with a one 132kV underground cable circuit and one spare duct from Lewes to tower PXB6, followed by installation of the second 132kV underground cable circuit along the same route M Replace tower PXB6 with a terminal L4 type tower and install outdoor sealing ends at Lewes Grid To support the N-2 recovery of half of Seaford before commissioning of the two cable circuits, replace 1km of 33kV cable section between Moulsecoomb and Rottingdean Dismantle the towers PO86 to PO16 Option 3 carries similar risks to Option 1. Option 4 - Create a new GSP to supply Lewes Grid before the single circuit PO route is dismantled - is 37.2M National Grid to construct and commission a new GSP at Horsted Green, install two 400/132kV transformers and two 132kV circuit breakers (estimated between 14.7 to 16.3M by National Grid) UK Power Networks to: Install two new 132kV underground circuits from Horsted Green to Lewes Grid Install four outdoor 132kV sealing ends (2 at Lewes Grid & 2 at the new GSP) and one new 132kV circuit breaker at Lewes Grid on PLB line Dismantle towers PO86 to PO16 SUMMARY OF PROPOSED STRATEGY The preferred approach is to create a new Grid Supply Point to supply Lewes Grid before the single circuit PO route is dismantled. This requires National Grid to construct and commission a new 2x240MVA 400/132kV substation in the vicinity of Little Horsted, East Sussex. The substation will: 6

8 - Avoid the need to asset replace the existing single circuit overhead line between Eastbourne and Lewes - Route PO - Maintain P2/6 Licence compliance to the Lewes and Newhaven group - Facilitate future reinforcement and re-configuration of the local network - Increase capacity headroom and therefore defer the need for future reinforcement at the adjacent Bolney and Ninfield GSPs A feasibility study undertaken with National Grid confirms the viability of establishing the new GSP adjacent to their existing 400kV double circuit south coast overhead line. The UK Power Network project deliverables are: - New switch house equipped with a two section GIS switchboard - 132kV double circuit cable connection between Little Horsted and Lewes substation - An additional 132kV switch panel at Lewes - Dismantlement of sections of Route PO The estimated cost and phasing of the works are 37.2M ( 31.4M in ED1): Description 2011 / / / / / / / / / /2021 PO Route Replacement Strategy ,176 4,498 5,245 6,366 6,291 5,837 4,821 2,876 MAJOR RISKS, ASSUMPTIONS, ISSUES & DEPENDENCIES Risks o Land purchase and planning permission at Little Horsted o National Grid outage constraints to connect the new super grid transformers o Street service congestion impacting on the open-cut cable route to Lewes 7