A case study, Online DGA during varying transformer conditions

Abstract

In this online DGA trial, fault-gas formation and moisture in a transformer was studied real time under varying transformer-operating conditions over roughly one-year period. Some recently updated data cover over 2 years. The main method used was to look if there was any correlation between gas levels or gassing rate and transformer operating conditions like loading, top oil temperature and estimated hot spot. During the study, the transformer was also degassed and the gases were monitored online during and after the degassing. The degassing process itself was efficient. However, soon after finishing the process some gas levels increased significantly whereas others not so much. This is discussed in this paper together with the actual measurement graphs. In addition, the performance of the online DGA monitor was studied by comparing the readings of the monitor to frequently taken oil samples analyzed in a laboratory. All 7 key fault gases were measured: methane (CH4), ethane (C2H6), ethylene (C2H4), acetylene (C2H2), carbon monoxide (CO), carbon dioxide (CO2) and hydrogen (H2).