Moyle

The Moyle Interconnector is a high-voltage direct current (HVDC) link connecting the electricity grids of Northern Ireland and Scotland. It runs between Auchencrosh in South Ayrshire, Scotland, and Ballycronan More in County Antrim, Northern Ireland. The interconnector has a total length of 63.5 km (39.5 mi), with a significant portion being submarine cable crossing the North Channel.

Technical Specifications

The Moyle Interconnector has a capacity of 500 megawatts (MW) and operates with a dual monopole configuration. Each pole consists of a coaxial 250 kV DC cable with integrated return conductors (IRC), providing a transmission capacity of 250 MW per cable. The converter stations were designed and constructed by Siemens and feature light-triggered thyristors, making them the first of their kind.

The interconnector uses Line Commutated Converter (LCC) technology, which offers lower losses and more efficient power transfer compared to other designs. However, this technology does not provide Black Start capability, unlike Voltage Sourced Converters.

History and Development

The concept of the Moyle Interconnector originated in the 1990s, with an interconnector agreement first signed between Northern Ireland Electricity and Scottish Power in 1991. Moyle Interconnector Limited was established in 1999 to construct the link. The project involved two main contractors: Nexans Norway AS for the cable systems and Siemens plc for the converter stations.

Construction took place during 2000 and 2001, with commissioning completed in December 2001. The interconnector began full commercial operation in April 2002, marking a significant milestone for Northern Ireland's electricity market by ending its isolation from larger electricity systems and markets in Great Britain and Europe.

Operational Challenges and Upgrades

The Moyle Interconnector has faced several operational challenges since its inception. In August 2011, it went out of service due to faults, but repairs restored it to 450 MW capacity by February 2012. However, further issues with the low voltage cables led to the interconnector operating at half capacity from June 2012.

To address these recurring problems, a major project was undertaken in 2015 to replace the low voltage parts of the Moyle cables. This involved laying new separate metallic return conductors (MRCs) to bypass the damaged integrated return conductors. The project, completed in 2016, restored the interconnector to its full 500 MW capacity.

Economic and System Benefits

The Moyle Interconnector provides significant benefits to consumers in Northern Ireland. It allows for the import of lower-cost power from Britain, which helps to reduce wholesale electricity prices in the single electricity market. A study conducted in the late 2000s estimated that customers saved over £100 million per year on average due to the lowering of wholesale prices.

Beyond economic benefits, the interconnector enhances system security. It can provide almost instantaneous power injection when the frequency of either the Northern Ireland or Great Britain transmission networks falls, offering mutual support during power station trips or other disruptions.

Recent Developments and Future Plans

In September 2024, important upgrades to the Moyle Interconnector were completed during a planned maintenance period. These upgrades included replacing the fire detection and control system, installing a new radiator bank on a converter transformer, and updating the HVDC control and protection system software.

Looking ahead, there are plans to increase the interconnector's capacity to meet growing demand. The System Operator for Northern Ireland (SONI) is proposing to connect Ballycronan More Converter Station directly to Ballylumford Power Station using two underground circuits. This project aims to strengthen security of supply, improve renewable energy integration, and increase interconnector capacity between Northern Ireland and Great Britain.

The Moyle Interconnector continues to play a crucial role in Northern Ireland's energy infrastructure, providing both economic and technical benefits to the region's electricity system.