Eltham-Sydenham
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LPN High Value Project Eltham-Sydenham 132kV Eltham – Sydenham Gas Cables Faisal Khanzada Justification Paper UK Power Networks (Operations) Limited. Registered in England and Wales. Registered No. 3870728. Registered Office: Newington House, 237 Southwark Bridge Road, London, SE1 6NP 1 132kV Eltham-Sydenham Gas Cables Working draft v0.1 Justification Paper Version 1.3 Document History Version Date Details Prepared by 1.0 20/06/13 Justification document Faisal Khanzada 1.1 24/06/2013 Updated Paul Elliott 1.2 24/06/2013 Updated Paul Elliott 1.3 24/06/2013 Final drafting Barry Hatton UK Power Networks (Operations) Limited. Registered in England and Wales. Registered No. 3870728. Registered Office: Newington House, 237 Southwark Bridge Road, London, SE1 6NP 2 132kV Eltham-Sydenham Gas Cables Working draft v0.1 Justification Paper Version 1.3 Contents 1.0 Business Objective ..................................................................................................... 4 2.0 Background ................................................................................................................ 4 3.0 Fault History ............................................................................................................... 5 4.0 Investment Drivers ..................................................................................................... 5 4.1 Gas cable and known issues .................................................................................. 5 4.2 Repair times and network security .......................................................................... 6 4.3 Availability of spares and repair costs ..................................................................... 6 5.0 Investement Options................................................................................................... 6 5.1 Recommended Option ............................................................................................ 6 5.2 Rejected Options .................................................................................................... 7 UK Power Networks (Operations) Limited. Registered in England and Wales. Registered No. 3870728. Registered Office: Newington House, 237 Southwark Bridge Road, London, SE1 6NP 3 132kV Eltham-Sydenham Gas Cables Working draft v0.1 Justification Paper Version 1.3 1.0 Business Objective The aim of this project is to minimise the risk of failure of 132kV gas cables and consequential risks to network security if they were to fail. Drivers- Safety, Network security, Public security Benefits- Network security, Resilience, Reinforcement of current assets. 2.0 Background The Eltham-Sydenham circuits are part of South London 132kV ring. The circuits are 132kV gas cables running between Eltham Grid to Sydenham substation. The cables are three core 0.6 sq. inch, installed in 1958. Each circuit is approximately 9.5 km in length. The circuits have a protracted history of gas leakage and in the last few years significant leaks have occurred on these circuits requiring extended outages to effect repair. In one particular event in 2010, the leak was so significant that all gas bottles pressurising the circuit required replacement twice every week. On several occasions even with continuous pumping of gas it has been extremely difficult to hold positive pressure on the cable. Failure to achieve continual positive gas pressure to the cable results in a breakdown of electrical integrity and an electrical fault. This also results in the ingress of water and once this has taken place the extent of the repair or replacement is significant. Since 2010 the circuits are inspected twice a week in order to ensure positive gas pressure to seek to avoid urgent outages and faults. Feedback from operational staff has also highlighted that the gas pressure monitoring equipment has also failed or provided incorrect information on several occasions which also drives the requirements for very frequent inspections. The majority of this cable route runs alongside a red route and hence access is severely constrained or even impossible in some circumstances. Any inspection, maintenance or repairs therefore presents significant logistical challenges. Figure 1 Single Line Diagram of 132kV Eltham-Sydenham Circuits UK Power Networks (Operations) Limited. Registered in England and Wales. Registered No. 3870728. Registered Office: Newington House, 237 Southwark Bridge Road, London, SE1 6NP 4 132kV Eltham-Sydenham Gas Cables Working draft v0.1 Justification Paper Version 1.3 3.0 Fault History Table 1 shows the history of 132kV Eltham- Sydenham gas circuits switched out due to gas leak. Circuit Description 2002 2003 2004 2005 2007 2008 2009 2010 2011 2012 Total ELTHAM 132kV - 1 1 1 2 1 1 3 2 2 14 SYDENHAM NO1 ELTHAM 132kV - 1 1 1 1 1 5 SYDENHAM NO2 Total 1 1 2 3 2 2 1 3 2 2 19 Table 1 Fault History Circuit Description 2002 2003 2004 2005 2007 2008 2009 2010 2011 2012 Total ELTHAM 132kV - 27 37 8 44 22 27 60 16 72 313 SYDENHAM NO1 ELTHAM 132kV - 1 12 6 13 1 33 SYDENHAM NO2 Total 27 37 9 56 28 40 1 60 16 72 346 Table 2 Outage Duration History Table 2 shows that on average two leaks every year requiring fault repair have occurred on the circuits. In total the loss of availability of at least one of the circuits is 346 days (Table 2). As stated in Section 2, such is the concern over the performance of the circuits and the associated monitoring equipment that since 2010 the system requires manual intervention twice a week. 4.0 Investment Drivers 4.1 Gas cable and known issues Gas insulated cables are widely accepted in the electricity industry to carry significant operating costs and risk due to the inherent design flaws that are known to exist. The design flaws associated with gas cables include gas leaks, cable faults, control tape fractures, lead sheath distension and thermal instability of the insulating papers. In particular, the issue of a double circuit outage is a significant concern, with both circuits feeding a primary substation of a similar gas cable construction. The failure mode most commonly encountered is the migration of cable impregnate. If the cable load is increased, even within its rating, the accumulated impregnate expands, causing mechanical damage to the cable construction or joints. It is widely accepted within the UK Power Networks (Operations) Limited. Registered in England and Wales. Registered No. 3870728. Registered Office: Newington House, 237 Southwark Bridge Road, London, SE1 6NP 5 132kV Eltham-Sydenham Gas Cables Working draft v0.1 Justification Paper Version 1.3 industry that the issues with gas cables are sufficiently severe to warrant their withdrawal from service. It is UK Power Networks policy to withdraw all gas cables from service by the end of the ED1 period. 4.2 Repair times and network security In comparison to other cable types, the repair of a gas cable takes a considerable amount of time. A typical repair time could easily be 16 weeks due to the length of time taken to de-gas the cable, locate the fault, obtain spares, effect the repair and depressurise the system. During this time, network security is severely compromised, because often the remaining healthy circuit is of an identical construction. Gas cables are prone to failure when the load on them is suddenly increased, as is the case for a single circuit outage. That means the second gas cable circuit is most likely to develop a fault when the first circuit is out of service. In terms of the Eltham – Sydenham circuits there are 15,000 customers at risk for a second circuit outage. UK Power Networks had first-hand experience phenomena of this during the replacement of the Laleham – Twickenham gas cable circuits in the SPN area. One circuit had been switched out for decommissioning when the now more heavily loaded second circuit faulted as a result of the additional load. As UK Power Networks were aware of this potential failure mode, additional reinforcement works had been carried out prior to this work taking place to mitigate this possibility. 4.3 Availability of spares and repair costs Spare parts for the gas pressurisation equipment, sealing ends and joints are now very difficult and expensive to source due to the lack of support offered by current cable manufacturers. There is also lack of suitable transition joints for use with modern XLPE cables. The typical cost for a gas cable repair is £200-£250k with a significant proportion of this cost being the excavation to locate and then fix the fault. The expertise to carry out the necessary jointing work is also very difficult to obtain. UK Power Networks has been forced on at least one occasion to call on the services of elderly, long retired jointers to provide the necessary technical advice. 5.0 Investment Options 5.1 Recommended Option The recommended option is to replace both gas circuits with XLPE cable. As detailed in “Asset Stewardship Report for Underground cables”, it is UK Power Networks strategy to replace all gas filled cables before the end of ED1. Replacement of gas filled cables have been phased throughout ED1 in order to make the programme deliverable in a practical sense. This particular circuit has been phased to fit with other asset replacement work taking UK Power Networks (Operations) Limited. Registered in England and Wales. Registered No. 3870728. Registered Office: Newington House, 237 Southwark Bridge Road, London, SE1 6NP 6 132kV Eltham-Sydenham Gas Cables Working draft v0.1 Justification Paper Version 1.3 place in the vicinity at the same time.