Identification of fault type is a critical component to dissolved gas analysis and assessing a transformer's condition. Fault conditions occur primarily from the thermal and electrical deterioration of oil and electrical insulation. Each combustible gas level will vary depending upon the fault process.
Arcing is the most severe of all fault processes. Large amounts of hydrogen and acetylene are produced, with minor quantities of methane and ethylene. Arcring occurs through high current and high temperture conditions. Carbon dioxide and carbon monoxide may also be formed if the fault involved cellulose. In some instances, the oil may become carbonized.
Corona is a low-energy electrical fault. Low-energy electrical discharges produce hydrogen and methane, with small quantities of ethane and ethylene. Comparable amounts of carbon monoxide and dioxide may result from discharge in cellulose.
Sparking occurs as an intermittent high voltage flashover without high current. Increased levels of methane and ethane are detected without concurrent increases in acetylene, ethylene or hydrogen.
Decomposition products include ethylene and methane, together with smaller quantities of hydrogen and ethane. Traces of acetylene may be formed if the fault is severe or involves electrical contacts.
Large quantities of carbon dioxide and carbon monoxide are evolved from overheated cellulose. Hydrocarbon gases, such as methane and ethylene, will be formed if the fault involved an oil-impregnated structure. A furanic compound and/or degree of polymerization analysis may be performed to further assess the condition of the insulating paper.
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