Importance of Calibrating Analytical Equipment for Detecting and Quantifying Degradation Byproducts of C4F7N/CO2/O2 Gas Mixtures Insulation Fluid

Author(s): Muhammad Bilal Arif, Christophe Coquelet, Maxime Lacuve, Frank Jacquier, Rachel Calvet.

In the past few years, the C4F7N/CO2/O2 gaseous blend has been recognized as the best promising alternatives to SF6 gas, allowing to keep the minimum dimensional and environmental footprint of high voltage power transmission equipment’s versus other alternatives. In the event of extreme thermoelectric stress, similar to SF6 the gas mixture undergoes dissociation and produces a diverse range of byproducts in various concentrations. Analytical technologies such as gas chromatography coupled to mass spectrometry (GC-MS) and Fourier Transform Infrared (FTIR) are the key devices that can have the accurate estimation of qualitative and quantitative measurements of byproduct gas samples. Analysis of the arced gas sample reveals a range of byproducts, including CO, CF4, C2F6, C3F8, C2F4, C3F6, COF2, CF3CN, C2F6CN, CF2=CF-CN, (CN)2, CF3-N=CF2, CF(CF3)2-CO-NH2, and (CH3)2SiF2 that can be found as trace-level. However, due to the limited availability of standard gas in the market, only five gases, CF4, C2F6, C3F8, CF3CN, and COF2 were selected as standard for quantification. In our GC-MS method development, achieving complete peak separation was not possible due to the potential matrix effect of the sample. However, the peak area corresponding to the molecular ion of CF4, C2F6, C3F8, CF3CN, and COF2 was carefully determined, and the regression curve was plotted for each molecule individually. In COF2 results, the standard deviation was 69%, which led us to develop the FTIR methodology for COF2 with the classical least squares (CLS) method, in which the standard deviation drops to 4% from 69%.