Return on Experience on the C4-FN/O2/CO2 Technology based on a GIS after 7 years in Operation

France. This GIS, operated by RTE and manufactured by GE Vernova also serves for a longterm study focused on the gas composition evolution. This was the 3rd dedicated measurement campaign, providing data since the GIS commissioning in November 2018.

The gas analyses were performed using five different mobile analysers. Four analysers were compared to a reference gas before transport. The fifth’s correction was determined based on the comparison with other devices. In total, all 59 gas compartments were analysed at least once, and 93 measures were performed.

The gas composition was determined to be very stable. Minor expected C4-FN and O2 increases were generally observed. These are lower than previously determined as the accuracy over 7 years is better. The humidity appears quite low although some analysers still show difficulty with that measurement. Normal CO traces were observed, with an outlier at 1600 ppm corresponding to a circuit-breaker with moderate switching activity.

The integrated digital pressure monitoring was used to estimate the leakage rates. The substation shows an average annual leakage rate of 0.22% over 7 years, and only 0.15%/year on the last 3.5 years, despite not having yet the new improved sealing against CO2 permeation.

All results are satisfactory, and no action is necessary. The GIS is in very good condition, showing nothing abnormal. The analyse will continue to capitalize furthermore on this unique dataset. Main task is to continue working on the reliability and accuracy of the mobile gas analysers.