eMISsion-free HV and MV transmiSION switchgear for AC and DC

Project Information

MISSION

Grant agreement ID: 101135484

DOI

10.3030/101135484

EC signature date 22 November 2023

Start date 1 January 2024

End date 31 December 2027

Funded under

• Climate, Energy and Mobility

Total cost

No data

EU contribution

€ 10 398 632,46

Coordinated by

SINTEF ENERGI AS
Norway

Periodic Reporting for period 1 - MISSION (eMISsion-free HV and MV transmiSION switchgear for AC and DC)

Reporting period: 2024-01-01 to 2025-06-30

Summary of the context and overall objectives of the project

To reach a climate-neutral society by 2050, we urgently need to cut down on fossil fuel use and greenhouse gas emissions. A key part of this transition is switching to renewable energy sources like wind and solar. By 2050, over 60% of our electricity is expected to come from these sources – which are often located far from where the power is actually needed.

To make this work, we need smarter and stronger power grids that can carry electricity over long distances. That means developing advanced technologies for transmitting electricity, especially using direct current (DC) systems at medium and high voltages. One crucial component in these systems is switchgear – devices that control and protect the flow of electricity.

Today, many switchgear systems use a gas called SF₆ for insulation. Unfortunately, SF₆ is the most powerful greenhouse gas known – one kilogram of it has the same warming effect as 24,300 kilograms of CO2. Leaks from equipment and handling of the gas contribute significantly to the grid’s overall emissions.

This is where the MISSION project comes in. Its goal is to develop and test three new types of switchgear that don’t use SF₆, helping pave the way for climate-friendly power transmission:

- A high-voltage AC circuit breaker without SF₆, developed by Siemens Energy and tested in Norway and France.
- A high-voltage DC gas-insulated switchgear (GIS), developed and tested in Germany.
- A medium-voltage DC circuit breaker, developed and tested by G&W.

The project will also study how different alternatives to SF₆ perform in both AC and DC systems.

By doing this, MISSION will help make energy transmission cleaner and more sustainable – supporting the shift to a resilient, climate-neutral electric grid.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The MISSION project aims to accelerate the transition to SF₆-free technologies in high-voltage power systems across Europe. It encompasses research, development, testing, and pilot deployment of innovative circuit breaker technologies for both AC and DC applications.
Work Performed Across Work Packages
• WP1: Developed scenarios for future European power grids, estimated SF₆ inventories, and assessed transition strategies. It also evaluated grid resilience and proposed environmental and economic impact metrics.
• WP2: Conducted high-precision measurements of electrical discharges in alternative gas mixtures (N2/O2/CO2), developed advanced computational models, and improved partial discharge detection methods.
• WP3: Defined type test requirements for 420 kV SF₆-free circuit breakers, planned pilot site monitoring strategies, and coordinated partner responsibilities for pilot deployment.
• WP4 & WP5: Designed and initiated testing of a 420 kV AC vacuum circuit breaker and a 550 kV HVDC GIS insulated with N2/O2, targeting SF₆-free operation.
• WP6: Developed and validated a 12 kV fast mechanical DC circuit breaker, including modelling, arc commutation analysis, and prototype testing. A full-system demonstration is planned.
• WP7 & WP8: Prepared pilot installations of SF₆-free 420 kV breakers in Norway and France, selected challenging substation environments, and planned monitoring under real grid conditions.
Main Achievements
• Significant SF₆ Emission Reduction Potential: Transition strategies show up to 65% reduction in emissions by 2100 compared to continued SF₆ use.
• Validated SF₆-Free Technologies: AC and DC breaker prototypes demonstrated promising performance in simulations and initial tests.
• Advanced Modelling and Measurement Tools: New models and test setups enable accurate prediction and analysis of discharge behaviour and breaker performance.
• Pilot Readiness: Two 420 kV SF₆-free breakers are ready for deployment in harsh and diverse European climates, marking a milestone toward industrialization.
• Collaborative Progress: Strong contributions from TSOs, manufacturers, and research institutions have ensured technical feasibility and alignment with market needs.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

WP1 – Grid of the Future
MISSION developed scenarios for Europe’s transition to SF₆-free technologies, quantifying emissions, equipment needs, and reliability. Accelerated adoption can cut emissions by up to 20% versus business-as-usual without compromising resilience. A vulnerability study found no new systemic risks but stressed the need for standardization and operational experience. Metrics for environmental and cost evaluation (LCA, LCC) were proposed to guide future decisions.

WP2 – SF₆ Alternatives for AC and DC Switchgear
The project advanced understanding of alternative gas mixtures through open-access swarm data and discharge models for N2/O2/CO2. A 1D breakdown model and 3D PD simulation framework were developed and validated experimentally. High-voltage test setups for breakdown and PD detection are operational, enabling systematic validation and supporting design of SF₆-free insulation systems.

WP3 – Technical Requirements and Pilot Planning
Type-test requirements for 420 kV SF₆-free circuit breakers were defined per IEC 62271-100, with additional tests for overhead lines and extreme climates. Two pilot sites were selected: Dagali (Norway) for severe cold (–50 °C) and Marsillon (France) for high temperatures (+40 °C). Monitoring plans include fault recorders, transient voltage tracking, gas density monitoring, and optional X-ray emission checks.

WP4 – 420 kV SF₆-Free Live-Tank Vacuum Circuit Breaker
The conceptual design of the 420 kV vacuum CB was completed with dielectric and thermal simulations confirming compliance. A prototype was built and tested, validating vacuum interruption and clean-air insulation at this voltage level. Mechanical endurance and switching performance were assessed, and preparations for full type testing are underway, marking a major step toward the first SF₆-free 420 kV AIS breaker at TRL 8.

WP5 – 550 kV HVDC GIS with N2/O2
A 550 kV DC GIS design using N2/O2 insulation was derived from AC GIS platforms and validated through dielectric withstand, temperature rise, and insulation system tests. New components such as RC dividers, zero-flux CTs, DC bushings, and surge arresters were developed. Manufacturing tools for critical parts have been ordered, and type testing is scheduled for 2026, positioning the project to deliver the first SF₆-free HVDC GIS at TRL 8.

WP6 – New Generation of Fast Mechanical MVDC Circuit Breakers (12 kV)
A PSCAD model for a 12 kV LC-type DC breaker was developed and validated, demonstrating interruption of up to 6.5 kA within 0.5–2 ms. A prototype ultrafast disconnector achieved >16 m/s opening speed and a 10 mm stroke in 1.6 ms, confirming rapid commutation feasibility. Experimental work on arc dynamics and dielectric recovery advanced understanding of post-arc behaviour. Next steps include TRL 6 system-level demonstration and industrial design for manufacturability, with scalability to 40–80 kV.