Update on C4FN mixture 245 kV and 420 kV metal enclosed switchgear

Benefiting of the same compactness and equivalent performances as the latest SF6 apparatus generation, the C4FN / O2 / CO2 gas mixture does not need any longer to demonstrate its viability to be an effective solution for high voltage circuit-breakers. Thanks to several technical achievements based on the C4FN alternative gas mixtures in the last decade, the latest complete development of the SF6-free 420 kV metal enclosed switchgear led the way for a common interrupter dedicated to multiple ranges. Combining different architectures for respective applications, this latest metal-enclosed switchgear version continues its development journey to reach key performance such as 245 kV and above.

This paper will make a particular focus on GIS circuit-breakers and on the efforts made for the standardization between the SF6-free 420 kV and the 245 kV switchgears. The shared circuitbreaker approach for single or double-chamber architecture is desirable to facilitate a standardization in the manufacturing process, the switch from one specification to another, and the transition toward more environmental-friendly solutions. This paper will also present updates on the technological progress achieved to extend the initial

SF6-free 420 kV 63 kA 50 Hz circuit-breaker up to 60 Hz performances. The double-chamber architecture completed its type-test qualification sequence over 2025 to fulfil the 362 kV 60 Hz application, addressing GIS for North America. Technical details are provided for this performance extension to highlight the main differences and challenges brought with the 60Hz under international standard requirements.

Then, the latest technical progress achieved for the 245 kV SF6-free circuit-breaker range updates on the progress and performances demonstrated on the current product 245 kV 50 kA 50 Hz will be given.

The extension to 245 kV 63 kA 60 Hz will be developed. Technical challenges solved during this development are reviewed to expose the readiness of the C4FN alternative gas for the stringent applications.