Jersey Electricity : £17m Town substation civil works complete

Work on the £17m St Helier West primary substation at the disused quarry at Westmount Gardens reaches another milestone this weekend with the completion of the complex civil works. Jersey Electricity's contractors Jayen have removed 27,000 tons of material including 5,000 tons of rock before piling to support the building slab and erecting a new retaining wall to protect the facility.

Next week specialist French contractors Engie INEO will move in and begin the actual substation build which is expected to take a year. This is the fourth time JE has used Engie INEO in such a project here, following Rue des Pres and Western primary substations and South Hill Switching Station, where the Normandie 3 subsea cable connects to Jersey's network.

St Helier West Project Manager Mark Vivian explained: 'On the mainland, substations of this size would normally be built outdoors. These installations are not overly aesthetically pleasing plus, wind-borne salt contamination is a problem on islands. On a visit to Normandy in 2000, our engineers realised that the French design of St Remy des Landes substation would be the best solution for Jersey and it has been used at Rue des Pres and Western primaries and South Hill. The design uses simple air insulated components integrated into the structure of the building. Crucially, it also means we can carry out our own maintenance and repairs without the expense of off-Island assistance in the event of plant failure.'

JE has undertaken much work since acquiring the 10,000sq ft site from the Parish of St Helier in September 2014. Identifying the ground conditions of this old coastal quarry site involved careful clearance and investigation of the site to ensure the specification for the civil works was properly scoped so that the old quarry wall could be safely removed while retaining the ground stability of the site. A total of 5km of cabling has also been laid to connect the substation to JE's complex network.

Siting of the substation was critical. It had to be to be located between Esplanade Primary and Queen's Road Primary and integrate into the existing 11kV and 90kV networks with minimal cable lengths but maximum cable separation to ensure resilience. The site also had to be accessible for maintenance but distanced enough from residential areas not to cause nuisance. Between 2009 and 2012, States Planning and Parish officials considered seven sites with Jersey Electricity before the Council of Ministers, the Constable and, Procureurs du Bien Public of St Helier backed the sale of the 10,000 sq ft old quarry site to Jersey Electricity for the sum of £250,000 in September 2014.

The new substation is essential to secure existing supplies to around 13,000 customers in the area as well as future proof the network to meet the increasing demand for electricity. The network in central and western St Helier has been at near full capacity for some time. Several circuits between Queen's Road and Esplanade Primary substations were installed over 50 years ago and have become stressed due to the present high electrical loadings.

Once in service, the new substation will remove the pressure on existing infrastructure and service around 70-80% of St Helier's demand. The new retaining wall will blend into the surrounding landscape and provide a public viewing platform overlooking St Aubin's Bay north of the substation. The station is scheduled to be in service late next year and the landscaping completed in 2019.

You can see how the finished substation will look in this video, a 3D walk-through of the project and surrounding area.