Gas in oil analysis-methods and equipment re-assessed

This paper describes a comparison of results obtained by the headspace dissolved gas analysis (DGA) technique used by PowerGen, with a reference Toepler gas extraction procedure, to detect fault gases in power transformers. The justification for the study was to establish a correlation between the results obtained by automated headspace gas analysis and a standard DGA method described in IEC 567. An additional objective was to investigate the reproducibility of the headspace analysis method. The study showed that the headspace method gives good reproducibility for individual fault gases. However, when the results obtained by the two methods were compared, it was evident that the Toepler reference method gives lower values for fault gas concentrations. The difference observed for each individual fault gas is reasonably consistent and therefore permits the results from the two methods to be brought to the same base if required. Finally, in view of the observed differences, it is preferable that the same analysis technique is used consistently to monitor changes in transformer oil fault gas concentrations over a period of time