From isolation to integration: enhancing Shetland's distribution system to connect HVDC

Shetland is GB’s largest electrically islanded distribution network. The world-class wind capacity factor resulted in over 600 MW of onshore wind contracting. This triggered an HVDC interconnection to the GB national grid with local 132 kV transmission infrastructure to supply the distribution network. As the new HVDC link is a single circuit, a solution for plan ned and unplanned outages is required to ensure security of supply. The solution must provide two elements: (i) the ability to ride through any transmission outage; and (ii) maintain the islanded network including supplying the demand on Shetland for up to 45 minutes until standby generation is running. Failure to provide both elements would result in a blackout across Shetland. A particular challenge relates to the fault ride through as up to 600 MW of generation begins to flow into the distribution network prior to protection disconnecting the transmission connected wind generation. This paper details the technology assessment and power system studies conducted. A regulated tender followed which selected a service provider offering a 106 MVA Battery Energy Storage System and 400 MW AC Chopper. Regulator funding was approved in December 2024 with project completion expected in the first half of 2026.