Dissolved gas analysis of faults in biodegradable oil transformer insulating systems

This paper presents results of experimental tests performed on laboratory models of transformer windings immersed in bio-degradable oil. The investigations covered three common types of transformer faults: partial discharge (PD), arcing and overheating. Dissolved hydro-carbon gas products generated by these three fault types in bio-degradable oil are analyzed and compared with existing dissolved gas analysis (DGA) interpretation methods for mineral oil insulation. The PD and arcing tests were performed in small test cells using mineral and vegetable oils, with and without insulated pressboards. The overheating test was performed by heating the oils in the oven. At the end of each test, an oil sample was extracted for dissolved gas and moisture measurement. The results show that existing DGA interpretation techniques need to be modified if they are to be used for insulation assessment of bio-degradable oil.