Decomposition of transformer oils: a new approach for the determination of dissolved gases

The possibility of using a staticheadspace sampling technique for introducing gases into a chromatograph and performing dissolved-gas analysis automatically was demonstrated in a previous work. The main drawback of the method was the relatively long time that the analytes take to equilibrate between the oil and the headspace. In this paper, the application of mechanical agitation to a viscous matrix to enhance diffusion of the species during the equilibration period was investigated together with the use of an improved nickel catalyst system and a new porous-layer open tubular chromatog~aphic column. The analytical performance of the technique is established and compared with that of method A of the ASTM D 3612 standard procedure. The comparison shows that the technique can be used to assess dissolved gases with the same precision (overall precision < 5 % at medium concentration) in a much shorter time (first sample in 55 min; 25 min for each subsequent sample) with a higher sensitivity of detection (0.6, 11, 11.2, 0.06, 0.09, 0.1, 0.05, 0.04, 0.04 and 0.2 ppm (v/v>+ for H2, 0 2 , Nz, CH4, CO, c029 C2H29 cZH4, CzH6 and C3H8, respectively). An excellent correlation was observed between the analytical results of the two techniques applied to 35 transformer oil samples. The high sensitivity of detection achieved means that transformer fault diagnosis can now be extended to equipment newly commissioned or apparatus other than open breathing equipment, where the total gas content in oil is very low.