Insulating fluids, generally mineral oils, are used in transformers. Under normal and mild conditions, there is very little decomposition. Occasionally however, overheating of the oil occurs and decomposition products are formed. If the concentration of these gases reaches a critical point, the chances of catastrophic transformer failure are high.

The ASTM D 3612 method describes in detail three different ways to extract gas from oil for analyzing:

A. Vacuum Extraction

The gases are extracted from the oil via a vacuum extraction device (usually by syringe) and analyzed via gas chromatography.

GC2010D Transformer Oil Dissolved Gas Analyzer adopts this method to extract the gas.

B. Stripper Column Extraction

Dissolved gases are extracted from a sample of oil by sparging the oil with the carrier gas on a stripper column containing a high surface area bead. The gases are then flushed from the stripper column into a gas chromatograph for analysis.

C. Headspace Sampling

An oil sample is brought into contact with a gas phase (headspace) in a closed vessel purged with Argon. As a result, a portion of a gas dissolved in the oil is transferred to the Headspace.