# SP Energy Networks Commissions Landmark 400 kV SF6-Free Gas-Insulated Substation at Legacy in North Wales

> Marking a major breakthrough in eco-friendly transmission switchgear, SP Energy Networks has energized the modernized Legacy 400/132 kV Grid Supply Point in North Wales, utilizing fluoronitrile-free Clean Air and vacuum technology across its 400 kV circuit breaker bays.

- **Publish Date:** 2026-09-21
- **Category:** transformers-grid
- **Reading Time:** 4 min
- **Original Source Citation:** [SP Energy Networks Infrastructure Press Office](https://www.spenergynetworks.co.uk/news/pages/legacy-400kv-sf6-free-gis-substation-energization-september-2026.aspx)
- **Tags:** SP Energy Networks, 400 kV, SF6-Free, GIS, Wales, UK, Substations
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## Eliminating Potent Greenhouse Gases from the 400 kV Transmission Grid

Sulfur hexafluoride (SF6) has been the dominant arc-quenching and insulating gas in high-voltage switchgear for half a century, but possesses a global warming potential 24,300 times that of CO2. The rebuilt Legacy substation replaces 1960s-era oil and SF6 breakers with state-of-the-art clean-air GIS.

Operating with technical air (purified nitrogen and oxygen) and sealed vacuum interrupters, the 400 kV GIS equipment achieves full 63 kA short-circuit interruption with zero fluorinated gases and zero global warming potential (GWP < 1).

## Dual 240 MVA Supergrid Transformers with Ester Dielectric Fluid

The substation upgrade includes two replacement 240 MVA 400/132 kV supergrid autotransformers filled with biodegradable synthetic ester liquid, providing superior fire safety and environmental protection near local water catchment zones.

Legacy Substation serves as the principal injection node for onshore wind generation across North Wales, demonstrating full compliance with forthcoming UK and European F-gas phase-out mandates.

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