Dissolved Gas Analysis - Analysis

Analysis

When gassing occurs in transformers there are several gases that are created. Enough useful information can be derived from nine gases so the additional gases are usually not examined. The nine gases examined are:

  • atmospheric gases: hydrogen, nitrogen and oxygen
  • oxides of carbon: carbon monoxide and carbon dioxide
  • hydrocarbons: acetylene, ethylene, methane and ethane

The gases extracted from the sample oil are injected into a gas chromatograph where the columns separate gases. The gases are injected into the chromatograph and transported through a column. The column selectively retards the sample gases and they are identified as they travel past a detector at different times. A plot of detector signal versus time is called the chromatogram.

The separated gases are detected by thermal conductivity detector for atmospheric gases, by flame ionization detector for hydrocarbons and oxides of carbon. A methanator is used to detect oxides of carbon by reducing them to methane, when they are in very low concentration.

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