# Inelfe Biscay Gulf 5,000 MW HVDC Interconnector Reaches 70% Completion as Converter Stations Enter Electromechanical Phase

> Inelfe, the joint venture between French TSO RTE and Spain’s Redeia, has announced that the 400 km Biscay Gulf submarine and underground HVDC link has surpassed 70% overall completion, with civil structures finished at the Gatika and Cubnezais converter stations and electromechanical installation of 400 kV converter transformers underway.

- **Publish Date:** 2026-09-28
- **Category:** transmission-substations
- **Reading Time:** 5 min
- **Original Source Citation:** [Inelfe (RTE & Redeia Joint Venture)](https://www.inelfe.eu/en/news/biscay-gulf-interconnection-reaches-70-percent-completion-gatika-cubnezais)
- **Tags:** Inelfe, Biscay Gulf, HVDC 400kV, RTE France, Redeia, Subsea Cable, Converter Transformer, Gatika, Cubnezais, Spain, France
- **Canonical URL:** https://voltformer.com/news/inelfe-biscay-gulf-5000mw-hvdc-reaches-70-percent-completion-gatika-cubnezais
- **Markdown Source:** https://voltformer.com/news/inelfe-biscay-gulf-5000mw-hvdc-reaches-70-percent-completion-gatika-cubnezais.md

## Doubling Iberian Interconnection Capacity to 5,000 MW

Designated as a Project of Common Interest (PCI) by the European Union, the Biscay Gulf project will nearly double the commercial electricity exchange capacity between Spain and France from 2,800 MW to 5,000 MW. The double-link system comprises 300 km of submarine cable traversing the deep Atlantic seabed and 100 km of underground terrestrial cables.

With major trenching and horizontal directional drilling (HDD) landfalls completed at Capbreton, Seignosse, and Le Porge in France, civil engineering contractors have handed over the converter station halls to electromechanical installation teams.

## 400 kV VSC Converter Transformers and Harmonic Filter Yards

At Gatika (near Bilbao, Spain) and Cubnezais (north of Bordeaux, France), assembly crews are installing single-phase 400 kV Voltage Source Converter (VSC) transformers supplied by Hitachi Energy. Designed for continuous bidirectional power flow, each unit features specialized high-voltage DC bushings, synthetic ester insulation fluids, and low-loss magnetic core laminations.

The converter stations incorporate compact gas-insulated switchgear (GIS) and active harmonic filter yards engineered to damp high-frequency resonance and prevent transient disturbances from propagating into the Spanish 400 kV and French 400 kV transmission grids.

## Paving the Way for Mid-2027 Commissioning Trials

Following the ongoing electromechanical assembly, pre-commissioning energization tests on auxiliary transformers and DC smoothing reactors are slated for early 2027, with end-to-end trial power flows scheduled for mid-2027 ahead of full commercial operation in 2028.

The interconnector is projected to prevent up to 14 TWh of clean solar and wind curtailment annually across the Iberian Peninsula, dramatically accelerating European decarbonization goals.

---
Related: [Power & Energy News Hub](https://voltformer.com/news.md) · [Voltformer Substation & Transformer Catalog](https://voltformer.com/catalog.md)