HVDC Moyle

The HVDC Moyle Interconnector is the 500 MW HVDC link between Auchencrosh, South Ayrshire in Scotland and Ballycronan More, County Antrim in Northern Ireland, which went into service in 2001. It is owned and operated by Mutual Energy.
Mutual Energy is a mutual company which manages the Moyle Interconnector (and some high pressure gas transmission assets including the Scotland - Northern Ireland Pipeline) for the benefit of Northern Ireland's energy consumers.
Work was completed in 2016 to replace the subsea sections of the LV return conductors with two new return cables. This was carried out by Nexans (Norway) with the aid of Morrows (N.I) and Romac Civil Engineering (N.I).
Specifications.
The HVDC Moyle Interconnector has a capacity of 500 MW. It consists of two coaxial 250 kV DC cables with integrated return conductors (IRC), each cable having a transmission capacity of 250 MW. The IRCs have failed through the events below, and their function restored by laying separate return conductors. The converter stations are equipped with light-triggered thyristors.
The converter station at Auchencrosh is connected via a single-circuit 275 kV overhead three-phase AC line, which is installed on delta-type pylon, to Coylton substation, where the connection with the high voltage grid of Great Britain takes place. The connection to Northern Ireland is then made through dual long monopolar cables, of which are submarine cables. The Ballycronan More converter station is connected into the Northern Ireland grid through two 275 kV circuits.
In August 2011, the interconnector went out of service. Repairs were made and the cable became operational again with 450 MW in February 2012. However, further faults meant that a major part of the interconnector had to be taken out of service until it could be augmented with the additional return cables, completed in 2016. This restored capacity to the full 500 MW.
In February 2017, the cable suffered another fault, halving capacity to 250 MW. However full capacity was restored in September 2017, following repairs by Nexans.
Intraday capacity trading is not available, but is being discussed.
Since November 2017 exports to Scotland are limited to 80 MW due to National Grid UK transmission constraints. However, 2-day ahead projections of wind in Scotland are used to allow flows of up to 300MW. The 80MW constraint is expected to rise to 500 MW by 2022
Moyle also provides frequency support services to both Eirgrid and National Grid. These services provide for fast change of power flow in the event of a network disturbance on either the NI or Scotland transmission systems.