All transformers generate gases to some extent at normal operating temperatures. But occasionally a gas-generating abnormality does occur within an operating transformer such as a local or general overheating, dielectric problems, or a combination of these. In electrical equipment, these abnormalities are called “faults”. Internal faults in oil produce the gaseous byproducts hydrogen (H2), methane (CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6). When cellulose is involved, the faults produce methane(CH4), hydrogen (H2), carbon monoxide (CO), and carbon dioxide (CO2). Each of these types of faults produces certain gases that are generally combustible.

Dissolve Gas Analysis (DGA) is a non-destructive way of diagnosing the condition of the transformer by analyzing the amount of the combustible gasses dissolved in the oil. Though it is not a deterministic way of determining the exact condition of the transformer, DGA can somehow establish the healthiness of a transformer.

IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers provides detailed procedures for analyzing gas from gas spaces or gas-collecting devices as well as gas dissolved in oil.

To make this article short, below is an excel program for analyzing the result of DGA based on Doernenburg Ratio and Rogers Ratio Methods, both discussed in the IEEE paper mentioned above.

Download the Excel Here