Moyle Interconnector Circuit Breaker Replacement Programme

Background

Mutual Energy Limited (MEL) owns and operates energy infrastructure for the long-term benefit of energy consumers in Northern Ireland. Moyle Interconnector Limited (MIL) owns the 500MW High Voltage Direct Current (HVDC) Moyle Interconnector, commissioned in 2001, linking Northern Ireland and Scotland. It is a vital asset for Northern Ireland's electricity grid and provides support to Great Britain when required The Moyle Interconnector has seventeen 275 kV circuit breakers across its two converter stations. The existing Siemens 3AQ2-EE circuit breakers were commissioned in 2001 and are approaching the stage at which significant refurbishment or replacement is required. Proposed Requirement The proposed replacement programme is driven by the age, condition and maintenance requirements of the existing circuit breakers, together with the need to address project-specific requirements. The existing Siemens 3AQ2-EE circuit breakers are approaching their major refurbishment stage. The replacement programme also provides an opportunity to improve controlled energisation performance for the converter transformers through addition of suitable and Point-on-Wave switching capability. The existing Moyle circuit breakers include equipment rated at 300 kV but incorporating 420 kV interrupters. Studies have identified a more onerous project-specific Transient Recovery Voltage (TRV) requirement associated with the low short-circuit ratio on the Scottish grid side of the converter. The replacement solution must meet this TRV duty and may require interrupters of a higher voltage class than the existing arrangements. Suppliers will be expected to propose a suitable solution and demonstrate compliance through appropriate studies, calculations and supporting test evidence. The initial requirement is expected to comprise four converter pole circuit breakers, with two breakers at each converter station. MIL is also considering:

• the progressive replacement of up to thirteen additional filter, transmission line and busbar coupler circuit breakers.
• The anticipated scope includes:
• design, engineering, manufacture, supply, installation, testing and commissioning;
• demonstration of compliance with the required electrical ratings and project-specific TRV duty;
• controlled-switching and Point-on-Wave capability;
• factory inspection and testing;
• delivery and site logistics;
• assessment of compatibility with existing foundations, structures, buswork, cabling, protection and control systems;
• associated civil, structural, electrical, protection and control modifications; and
• training, recommended spares, specialist tools and through-life technical support.

The initial four circuit breakers are currently intended to be replaced during the planned summer outages in 2028 and 2029. The final scope, technical solution, procurement structure and allocation of responsibilities will be informed by this market engagement and remain subject to the relevant approvals. NB The estimated contract dates included below are purely indicative as the notice requires dates to be included and they may move.