Comparison between headspace and vacuum gas extraction techniques for the gas chromatographic determination of dissolved gases from transformer insulating oils

The conventional headspace sampling technique is highly efficient for analyzing dissolved gases in transformer oil apart from the relatively long time that the analytes take to equilibrate between the sample and vapor phases. By mixing the sample during the equilibration period, the equilibration time was shortened by a factor of 15. Under these conditions, analysis of the gases of the first sample is completed in 32 min, while analysis of each subsequent sample takes only 20 min. The results of the analysis of dissolved-gas standards by the headspace sampling technique were compared to those obtained by four labs using the ASTM D3612 method. Our technique compares well to the vacuum gas extraction technique with a number of accurate analyses higher than the best results obtained by the participating labs. An average relative standard deviation of 4% for all gases studied was observed. Excellent correlation between the results of the analysis of 80 transformer oil samples by these two techniques was noted for all gases of interest