Learnings

Outcomes

The Threepwood report conclusions are summarised below;

• A 33kV compressed dry air switchgear solution has not been presented to the ENA panel for consideration and approval due to the technology not being ready;
• Alternative insulation mediums are available, but they have a larger footprint than the SF6 33kV switchgear; a substantial remodelling and substation expansion would be required to replace existing SF6 equipment;
• Modelling demonstrates no cost benefit to introduce compressed dry air;
• Positively, there are no major technical barriers to compressed dry air as an alternative to SF6 but it’s still at the design stage;
• Currently, there is only one company - Nuventura developing a compressed dry air solution. This technology still must undergo and achieve two remaining type-tests, which will prove the electrical safety and suitability of the design;
• DNOs should develop a strategy to move away from their reliance on SF6 as an insulation medium and outline an implementation plan. This will help determine the timescales and allow SF6 insulation alternatives to be selected for investment. This will then allow elements of the implementation plan to be addressed such as SF6 free switchgear specification development;
• New switchgear products that no longer use SF6 as an insulation medium but have the same footprint are more likely to be produced first for the world-wide market before coming into the UK. As the products will be designed for the world-wide market, the operational acceptance phase of the implementation plan will need to focus on what modifications or additions are required to comply with UK Operational Safety Requirements.

There has been no change to the technical readiness level of 33kV compress dry air switchgear, as it was a desk-top study.

Lessons Learnt

As a result of this investigative project we have developed a snapshot of the level of development of 33kV switchgear alternatives to SF6 at the current time. This document could be used positively by other Distribution Network Owners to select a preference in emerging insulation technology, which best matches their network parameters and supports their future 33kV switchgear procurement programmes. This snapshot of 33kV switchgear alternatives for SF6 also could be used as a baseline to measure the onward development within the market.

All approached manufacturers supply the 33kV switchgear market world-wide. It is important to note that electrical products have to be made specifically or adapted for the UK market, so they are housed and maintained in a way that aligns with present UK Operational Safety Requirements, this incurs additional costs. The UK 33kV switchgear is a relatively small market comparing to the world-wide one, therefore there are greater world-wide influential factors that will stimulate changes in insulation mediums away from SF6. As it is more likely that a new switchgear product will come from the world-wide market the operational acceptability and commission phases of the implementation plan will take longer to ensure inclusion of appropriate UK system safety de-risking measures.

This project was a desk-based study, further research is required once an alternative solution to SF6 switchgear is ready for the operational acceptance phase of the implementation plan. This will develop the functional understanding and the technical documentation suitable for SF6 free 33kV switchgear to move towards BaU.