Phase-out SF6, phase-in F-gas-free alternatives

In 2018, TransnetBW started a long journey to replace SF6 in its electrical equipment with more sustainable solutions. The natural origin gases (NOGs) or gas mixtures with a GWP ≤ 1 have been preferred as SF6 alternatives from the beginning. Based on experience from own projects, market analysis and considering the latest requirements by policy-makers, TransnetBW published its own strategy on how to replace SF6 only with NOG-based alternatives in 2022. This strategy is being carefully considered in all grid expansion projects, in order to ensure the availability of equipment and avoid delays in its implementation. Thes strategy is compliant with the present F-gas-Regulation requirements.

Based on this strategy, TransnetBW stopped installing SF6-equipment below 123 kV in 2023. Since then, several NOG-based instrument transformers (ITs) and circuit breakers (CBs) have been installed and have been working flawlessly. Selecting NOGs as an alternative to SF6 is seen as both a sustainable and future-proof solution. NOGs are safer to handle, with lower operation costs and lower toxicity of the by-products in comparison to other alternatives and SF6. Furthermore, NOGs are not prone to be affected by incoming regulations (new revision of F-gas Regulation, PFAS Regulation etc.). 

Due to the very good experience gathered with SF6 instrument transformers (ITs), their replacement with NOG-based ITs rather than oil-insulated ITs is preferred by TransnetBW. They match the existing configuration of the substation (bay width) and only the foundations may need to be reinforced in some cases. Currently, there are about 120 oil-ITs (123 and 420 kV) in operation in the TransnetBW grid which are approaching their technical end of life and are planned to be replaced with SF6-free ITs based on N2/O2 over the coming years. The selection of NOGs in insulation systems provides for synergy effects in terms of grid operation and maintenance, as both prequalified manufacturers use the same gas mixture. The same gas handling devices can thus be used for gas quality checks, refilling can be performed from the same cylinder, no additional expertise is needed etc.

With regard to CBs, there are two technologies on the market which are compliant with the TransnetBW strategy and current F-gas-Regulation. The first one is based on N2/O2 as insulation medium and a vacuum interrupter for arc quenching. The second technology uses a gas mixture of CO2 and O2 for both insulation and arc quenching. CBs using technologies of this type are already on the market for up to 123 kV and most applications are already covered. On the 420-kV level, there are currently pilot projects being initiated at TransnetBW to install new NOG-based CBs as well. It is planned to use both technologies (N2/O2 with vacuum interrupter and CO2/O2) and commissioning is scheduled for 2027.

As far as 420-kV GIS is concerned, this remains the ultimate solution for those cases where an AIS substation cannot be accommodated. However, a NOG-based GIS remains the first option ahead of other solutions based on F-gases. The decision will be taken on a case-by-case basis in order to avoid delays in grid expansion and to remain compliant with the F-gas-Regulation at any time.