Abstract

According to the new F-gas regulation, entry into force in February 2024, from 2035, the use of virgin SF6, as insulating gas in electrical switchgear equipment (GIS), is prohibited. Depending on the voltage levels fluorinated greenhouse gases with a GWP >1 used as insulating or breaking medium in switchgear are also prohibited with time scales from 2026 (MV equipment) to 2032 (HV equipment). Existing assets are also concerned due to the ban of use virgin SF6 even for maintenance purpose. A study regarding the possible retrofilling solutions of existing 245 kV and 420 kV equipment is the scope of this paper. This work has been conducted within a three-party collaboration with a transmission system operator (TSO), a neutral research centre and a manufacturer of GIS. Due to its GWP<1 synthetic air, composed of 80% N2/ 20% O2, has been taken into consideration for these investigations. The main constraint in the retrofilling is the fact that the enclosures and all the main parts are not meant to be replaced. That means that the possibility for pressure increase with a new insulating gas is limited. Different evaluations and testing campaigns have been conducted to investigate the feasibility of this solution:

• A study, including bursting tests, has been conducted with the manufacturer of the equipment to see if the pressure, without changing the design, could be increased.
• Dielectric tests have been conducted in a real scale GIS set up to investigate the dielectric properties of synthetic air at 0,6 MPa, 0,8 MPa and 1 MPa.
• The electric field in the equipment has been studied via Finite Element Method (FEM) simulations. This study provides insight on the maximum stress at which the equipment is subjected.
• Synthetic air presents worst thermal properties than SF6 thus a continuous current test has been conducted in the passive compartments of a 420 kV GIS.

In conclusion of the pressure study a new design pressure has been defined, 0,72 MPa with respect to the old 0,5 MPa. Despite this pressure increase, comparing the dielectric strength resulted from investigations to the electric stress calculated for type test requirements and the continuous current test results, the use of synthetic air as a retrofilling alternative to SF6 seems impossible.

In conclusion of the feasibility studies, synthetic air gas has been discarded as retrofilling alternative to SF6 in these types of equipment

Caterina Toigo (SuperGrid Institute), Victor Petit (SuperGrid Institute), Lydie Cossedu (MasterGrid), Michael Inversin (RTE), Vivien Dona (MasterGrid), Alain Girodet (SuperGrid Institute), Marie Laure Allard (RTE)

Presented at CIGRE 2025 International Symposium