GB TransmissionNETS, 2025/26
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About this network

What this is

This is the existing National Electricity Transmission System in ETYS year 1, 2025/26. The tables come from Appendix B of ETYS 2025. Sheets of changes from 2026/27 onward are not drawn. England and Wales circuits are drawn at 275 kV and 400 kV. Scotland and the OFTO sheets are also drawn at 132 kV and 220 kV where the year-1 table says so. OFTO export cables at 150 kV and 155 kV are drawn. 33 kV collector circuits stay in the tables and are not drawn.

Owners

The year-1 sheets are SHE Transmission, SP Transmission, National Grid Electricity Transmission, and the OFTO circuits, transformers and compensators. A ± kV row in the OFTO circuit sheet is treated as HVDC, not as an AC circuit.

Generation

Generation is the TEC register in ETYS 2025 Appendix F, dated 31 October 2025. The diagram uses the published column MW Connected. The file does not mark embedded and directly connected plant separately, and it has no node code. A project is drawn only when MW Connected is above zero, the connection-site name matches exactly one transmission site, and that site is on the diagram. The marker is the connection site and uses the same style as any other station. The detail shows an Estimated sign when that position was inferred. Generation markers appear when you zoom in. Staged rows that share a project name and a connection site are not added together. A project with no unique transmission-site match is omitted.

Demand

Demand is Appendix G, user-submitted Grid Supply Point winter-peak MW. It is not a Future Energy Scenarios table and it has no Holistic Transition or other scenario split. Demand labels appear when you zoom in. The diagram label is the 2025/26 figure for the joined station. Later years stay in the table. The workbook prints 31/32 on both of the last two columns; the second column is kept on its own and is not treated as a different scenario.

Boundaries

All 34 lines from the NESO ETYS 2024 boundary GIS of March 2025 are included. The boundary layer starts on. Every boundary is the same colour, drawn at 25% opacity, so it does not cover the network. With the layer on and no boundary chosen, all of those lines are drawn. Choosing one in the filter draws only that line. A line can filter the diagram and the tables only where gb-network/raw/boundary_sides.csv has a reviewed exporting side. The other lines are drawn when the layer is on and no boundary is chosen, and they are not a filter. Study closures used to test which side a station is on are not drawn. Where the 2024 B2 line disagrees with the ETYS 2025 text, Errochty, Tummel, Tummel Bridge, Kinardochy, Clunie and Rannoch stay on the exporting side of B2, and the card says so.

HVDC

In-service links are drawn. That includes the three Caithness–Moray–Shetland sections and the Dogger Bank A ±320 kV OFTO cable. Central DC Substation has no published coordinate, so its position is fitted to the three published lengths. The detail shows an Estimated sign. Western HVDC Link is drawn between Flintshire Bridge and the Hunterston converter. Eastern Green Link 1 and 2, Eastern Green Link 3, Eastern HVDC Link 4, PSDC, Western Isles and Sealink are future schemes. They stay in the table and are not drawn.

What the diagram is not

The drawing is a diagram fitted to geography. Straight lines and the solid purple HVDC curves are not surveyed routes. A station that failed the marker check is still drawn when a position can be inferred, in the same style as a checked station. The detail shows an Estimated sign. A name in the site index with no transmission circuit, transformer, compensator or in-service HVDC link is left out. Appendix B has no quadrature-booster sheet, so phase-shifting transformers are not identified. Fault levels are the SSEN year-1 winter and summer tables only. There is no distribution network, no power flow, and no dynamic model.

Licences and checks