Table 4 Oil-immersed transformer fault types and causes

PD

Discharge phenomenon occurring due to gas bubbles produced, e.g., by drying defects or oil infusion defects and voids in paper

D1

Include spark-type partial discharge or low-energy arcs and carbonized perforation in the paper

D2

Significant damage to paper, formation of large quantities of carbon parties in oil, metal dissolution, and device tripping by gas alarms resulting from perforations due to high–energy arcs, flashovers, and short circuits

T1

Overload or oil flow duct blockage. Paper discoloration: Brown (\(<200^\circ{\rm C}\)), black or carbonize (> \(300^\circ{\rm C}\))

T2

Occurrence of carbonization of paper or formation of carbon in oil, e.g. to contact faults, welding defects, or circulating current

T3

Occurrence of formation of large quantities of carbon parties in oil, for example, excessive circulation of current in the tank or iron core or lamination layer short circuit

DT

Electrical abnormalities