Dissolved Gas Analysis	Interpretation	Acceptable Limits
Hydrogen* H 2	Thermal decomposition of the cellulose insulation material - overheating condition.	500 ppm (0.05%) (Max.)
Methane* CH 4	Overheating or other fault conditions have occurred or exist inside the transformer.	100 ppm (0.010%) (Max.)
Ethane* C 2H 6	Low energy arcing has occurred or exists inside the transformer.	50 ppm (0.005%) (Max.)
Ethylene* C 2H 4	Transformer is operating hot or localized overheating has occurred or exists.	50 ppm (0.005%) (Max.)
Acetylene* C 2H 2	High energy arcing has occurred or exists inside the transformer.	0 ppm (0.00%) (Max.)
Oxygen O 2	Thermal decomposition of the cellulose insulation material - overheating condition.	20,000 ppm (2.00%) (Max.)
CarbonMonoxide* CO	Thermal decomposition of the cellulose insulation material - overheating condition.	1,000 ppm (0.10%) (Max.)
Carbon Dioxide CO 2	Thermal decomposition of the cellulose insulation material - overheating condition.	10,000 ppm (1.00%) (Max.)
* Combustible Gas

Oil Screen Analysis	Interpretation	Acceptable Limits
Moisture Content	Reveals if transformer tank is sealed or cellulosic breakdown via the level of water present.	25 ppm ↓ 69KV XFRM (Max.) 35 ppm ↑ 69KV XFRM (Max.)
Interfacial Tension	Reveals the presence of sludge. Precursor to the insulation’s failure to properly cool the unit.	24 dyne/cm (Min.)
Acid Number	The amount of acidic or alkaline material present.	0.20 mg KOH/g-oil (Max.)
Color Number	Elevated number indicates oil contamination or deterioration of the oil.	0.5 (New Oil) – 8.0 (Worse case )
Dielectric Breakdown	Reveals conductive contaminants in the oil such as metallic cuttings, fibers or free water.	24 KVAC (Min.)
Specific Gravity	Helps reveal if oil has been mixed with other fluids.	Approx 0.875 @15°C
Power Factor	Reveals leakage current through oil. Elevated power factor reveals moisture, resins or fuel oils.	0.5% ↓ 69KV XFRM @ 25°C 1.0% ↑ 69KV XFRM @ 25°C (Max.)