History and development


The Moyle Interconnector links the electricity grids of Northern Ireland and Scotland through submarine cables running between converter stations at Ballycronan More in Islandmagee, County Antrim and Auchencrosh in Ayrshire. The link has a capacity of 500MW.

The commissioning of the Moyle Interconnector marked a real watershed for the electricity consumers and economy of Northern Ireland. When it went into commercial operation in early 2002, it ended the isolation of Northern Ireland from the much larger electricity systems and markets of Great Britain and the European mainland, where interconnection of national electricity systems has been the norm for many years. It has made a major contribution to the drive for lower electricity prices in Northern Ireland, which has a history of high energy costs.

The Moyle Interconnector has enhanced the security of electricity supply throughout Ireland and reduced the costs of running the electricity system. It now provides competition in the electricity market arrangements in Ireland and makes possible trading with our neighbouring market in Great Britain. The Moyle Interconnector transmission capacity is available for third party access, i.e. to anybody who wants to trade in electricity in either direction between Ireland and Great Britain or beyond.

The Single Electricity Market (SEM) for the island of Ireland went live on 1st November 2007. The current electricity market in Great Britain – the British Electricity Trading and Transmission Arrangements (BETTA) came into effect in April 2005. The Moyle Interconnector provides the vital link for trade between the new electricity markets of Ireland and Great Britain.

Electrical interconnection between Northern Ireland and Scotland had been considered for more than thirty years before the Moyle Interconnector project began in 1990. Early studies had established that direct current (DC) interconnection would be superior to the alternating current (AC) alternative both technically and economically and this was confirmed in subsequent feasibility studies.

The study carried out in 1990, which included the first seabed survey, led to the signing of the initial interconnector agreement between Northern Ireland Electricity (NIE) and Scottish Power. Following a protracted planning process, including Public Inquires in Northern Ireland and Scotland, the last of the main consents was granted in 1998 with detailed planning permission for the converter stations following in 2000.

Key Dates
1990 First Seabed Survey
1991 Initial interconnector agreement between Northern Ireland Electricity and Scottish Power
1993 Applications made in Northern Ireland and Scotland for consent for the converter stations, cables and overhead lines.
1994 Consent granted for installation of undersea cables by the Department of Transport.
1994/1995 Public enquiries held in Scotland and Northern Ireland
1997 Consent granted for overhead line construction.
1998 Outline planning permission for converter station on Islandmagee granted
1999 Contract awarded to Siemens for construction of converter stations.
Contract awarded to Nexans for submarine and underground cables.
2000 Detailed planning permission granted for converter stations
Scottish overhead line contract awarded to Balfour Beatty
2001 Construction & Testing
2002 Full Operation

The configuration of the Moyle Interconnector was chosen to provide the high reliability required of a link that was expected to be the equal largest infeed to the Irish electricity system for many years. Implementation involved the construction of High Voltage Direct Current (HVDC) converter stations of 2x250MW dual monopole design in Northern Ireland and Scotland, the installation of an underground and submarine DC cable system consisting of two separate 250 MW cables running the 63km route length between the stations and the construction of 64km of 275kV AC overhead line in Scotland.

In 1999, Moyle Interconnector Limited (Moyle), was established within Viridian Group PLC to construct the link. At the end of that year, Moyle awarded two turnkey contracts for the design, manufacture, installation and commissioning of the major elements of the interconnector. Nexans Norway AS was the supplier of the cable systems, while Siemens plc provided the converter stations connected to the transmission systems in Northern Ireland and Scotland.

In 2000, Scottish Power awarded the contract for construction of 64km of 275kV single circuit overhead line from their existing Coylton substation to Moyle’s converter station at Auchencrosh. Balfour Beatty was the contractor.

Manufacture and construction took place during 2000 and 2001. The Moyle Interconnector was commissioned in December 2001 and, after a trial operation period, began full commercial operation in April 2002.

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