Transformer Fault Diagnosis by Dissolved-Gas Analysis

The great majority of incipient faults occurring in power transformers gives evidence of their presence early in their developmental stages. Oil and oil-impregnated electrical insulating materials can decompose under the influence of thermal and electrical stresses generating gaseous decomposition products which dissolve in the mineral oil. The nature and the amount of the individual component gases extracted from the oil may be indicative of the type and degree of the abnormality present [1]. One out of four transformers tested, using a gas chromatography technique, has an operational fault. Data obtained from the analysis of nearly 5000 transformers considers units ranging in size from 25 kVA-300 MVA. Case histories comparing fault diagnosis with actual conditions are cited. A method of determining the severity of the problem will be demonstrated. Over three years of experience using this method has proved the practical value of this chemical analytical tool to the power engineer.