Geraint Hancock, contract delivery manager with Central Networks Infrastructure Services, updates on progress at the new Port Ham switching station.
Port Ham interconnector switching station, on the banks of the River Severn just outside Gloucester, is a grid supply point (GSP). It takes electricity at 132kV from the National Grid substation, a few miles away at Walham, and feeds it into the Central Networks distribution network. Through a network of primary and secondary substations, this network feeds over 240,000 customers in Gloucestershire, Herefordshire and much of south and east Worcestershire.
The original outdoor station, built in the early 1950s, had experienced above-average load growth, to a current peak load of 672MVA. The AIS (air insulated switchgear) had reached the end of its useful life. So in 2002 we decided to completely rebuild the facility to ensure continued reliability of supply, as well as to provide scope for further load growth.
Initially, the project was tendered in the expectation that the AIS would be replaced on a like-for-like basis. However, in consultation with the ABB and Balfour Beatty consortium, we decided that building a new indoor GIS (gas insulated switchgear) station would offer a number of important advantages, at around the same overall cost of impressed that ABB’s state of the art compact ELK-04 (GIS) switchgear solution could be condensed into just one-fifth of the space used by the existing station. Port Ham is in an important nature conservation area. The smaller switchgear has allowed us to meet planning concerns by housing the station in a low-profile building designed to blend in with the local environment.
LIMITED DOWNTIME
In addition to saving space, GIS also offered two further advantages. First, we have been able to reduce circuit downtime, as the new GIS circuits could be constructed with the existing units still in service. Downtime was limited to the rerouting of the network connections. This was a crucial factor, because of the critical position of Port Ham in the supply network. Second, the GIS was constructed outside the existing live compound, considerably reducing health and safety risks to personnel working on site.
PILING
One of the major project challenges was the soft ground - on the flood plain of the River Severn - which required major foundation work before construction could begin. It was certainly impressive to see the project team driving some 120 cast concrete piles down 15 metres to the bedrock in just over 10 days. The building itself has been raised on stilts to ensure that the switchgear is at least one metre above the predicted level of the once in 100 years flood level.
FLAGSHIP PROJECT
The new indoor switching station comprises 20 bays of GIS switchgear: 12 feeder circuits; four National Grid incomers; two bus couplers; and two bus sections. The size of the investment and the strategic importance of Port Ham has made it a flagship project for Central Networks. And we have been particularly keen to use it both to gain experience of applying GIS technology in challenging applications, and to develop a model approach to the delivery of large capital projects.
We have been very pleased with progress to date. During the summer, a key milestone was passed with the successful energisation of the interconnector circuit. Eight out of the 16 circuits were transferred by the end of October - putting us bang on target to have Port Ham fully commissioned for the end of 2006.