Retrofill application of 420 kV Gas Insulated lines with fluoronitrile based gas mixture

The latest introduction of high-voltage equipment on the market has seen substantial innovations and technological transformations to offer SF6-free solutions. In this context, a new generation of gas-insulated switchgear has been designed and industrialized by manufacturers.

It is well known that this objective has been achieved using a gas mixture based on fluoronitrile

(C4F7N), carbon dioxide (CO2), and oxygen (O2). Combined with new product designs, this has demonstrated many advantages in terms of dielectric withstand, thermal properties, and dimensional footprint comparable to SF6 equipment. However, dismantling the installed product base, which still has 10 or more years of lifetime remaining, is not economically viable.

This paper explores the technical feasibility of retrofilling gas-insulated lines (GIL) by substituting SF6 with a C4F7N-based gas mixture, focusing specifically on dielectric withstand, temperature rise, and tightness performance. The project presented focuses on a retrofill application for a 420kV GIL, supported and co-funded by the European Commission under a

Program for the Environment and Climate Action sub-program named “SECOND LIFE GIS”

(Project 101113840 — LIFE22-CCM-FR-SECO2ND LIFE GIS). Based on IEC standard requirements, 420kV performance has been evaluated to determine the viability of this innovative solution.

From the manufacturer's perspective, the qualification process is faster and cheaper compared to installing new products, since only part of the type tests needs to be performed. For TSOs, the main parts of the equipment can be reused, resulting in cost savings and a reduction of environmental impact.