Moyle Interconnector, Co Antrim

The construction of the 500MW Moyle Interconnector between Scotland and Northern Ireland was the first HVDC (high voltage direct current) link between the electricity grids of Northern Ireland and mainland Britain, opening up trade between the British and European electricity markets and the previously isolated Northern Ireland market.

The Moyle Interconnector is comprised of two 55km submarine cables, 64km of overhead high voltage electricity lines, two poles which are both capable of transmitting 250MV in both directions and two converter stations and associated AC switchyards, situated at Auchencrosh, Ayrshire in Scotland and Ballycronan More, Islandmagee in Northern Ireland.

Siemens AG were appointed to provide the design services for the converter stations and Doran Consulting, in a design and construction contract with Farrans Construction Limited, undertook the civil and structural engineering design for both of these converter stations and associated switchyards.

Each site presented different ground conditions, with the site at Ballycronan More requiring extensive earthworks to regrade an existing valley and provide a level platform for the station and switchyard.  Due to the limitations on movement for the electrical equipment, extensive piled foundations were adopted for both the converter station and switchyard.

Auchencrosh sits on silty clay overlying rock, which meant that extensive rock breaking was required to create the platform for the station and switchguard. Temporary surface water ditches were required around the platform, complete with silt ponds, to prevent contamination of the nearby watercourses and loch during the construction process.

Each converter station is comprised of a 2-storey control building, valve halls, DC switchguard, valve cooling and air conditioning rooms and six transformer bays, which were separated from the halls by reinforced concrete firewalls. The walls were designed for loading from a pulling attachment for the transformer installation and cast in rails were incorporated into the reinforced concrete plinth onto which the transformers are located.  A stone filled flame trap and oil containment bund was required around each transformer.

We also provided design services in relation to the additional auxiliary buildings which were required. These were located around the converter station and the AC switchguard and were comprised of an underground fire fighting and pump house, spare transformer bund, spares storage facility and generator buildings.