(1) Electrical discharge - visually detectable faults defined by IEC 60599
Partial discharge (PD): Possible X-wax deposition, pin holes or carbonized perforation in paper
Discharge of low energy: Large carbonized perforation through paper, carbonization of paper surface, or carbon particles in oil
Discharge of high energy: Extensive destruction and carbonization of paper, metal fusion at the discharge location, extensive carbonization in oil, in some cases tripping of equipment
(2) Thermal faults - visually detectable faults defined by IEC 60599
Thermal faults, in oil or/and in paper, below 300℃ if the paper has turned brownish and above 300℃ if the paper has carbonized
Thermal faults of temperature above 700℃ if there is strong evidence of carbonization of the oil, metal coloration(800℃) or metal fusion (>1000℃)
(3) Suggested ratios:
C2H2/C2H4, CH4/H2, C2H4/C2H6
Range of 90% typical concentration values observed in power transformers (all types) (ppm in volume)
Incremental ratios of CO2/CO less than 3 are generally considered as an indication of probable paper involvement in a fault.