IEEE C57.104-1991 pdf free.IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers.
IEEE C57.104 decomposition of oil-impregnated cellulose insulation produces carbon oxides (CO, CO2) and somehydrogen or methane (H), CHa) due to the oil (CO, is not a combustible gas).The rate at which they are produceddepends exponentially on the temperature and directly on the volume of material at that temperature. Because of thevolume effect, a large, heated volume of insulation at moderate temperature will produce the same quantity of gas asa smaller volume at a higher temperature.
Mineral transformer oils are mixtures of many different hydrocarbon molecules, and the decomposition processes forthese hydrocarbons in thermal or electrical faults are complex. The fundamental steps are the breaking of carbon-hydrogen and carbon-carbon bonds.Active hydrogen atoms and hydrocarbon fragments are formed. These freeradicals can combine with each other to form gases, molecular hydrogen, methane, ethane, etc., or can recombine toform new,condensable molecules. Further decomposition and rearrangement processes lead to the formation ofproducts such as ethylene and acetylene and, in the extreme, to modestly hydrogenated carbon in particulate form.These processes are dependent on the presence of individual hydrocarbons，on the distribution of energy andtemperature in the neighborhood of the fault, and on the time during which the oil is thermally or electrically stressed.These reactions occur stoichiometrically; therefore,the specific degradations of the transformer oil hydrocarbonensembles and the fault conditions cannot be predicted reliably from chemical kinetic considerations. An alternativeapproach is to assume that all hydrocarbons in the oil are decomposed into the same products and that each product isin equilibrium with all the others. Thermodynamic models permit calculation of the partial pressure of each gaseousproduct as a function of temperature, using known equilibrium constants for the relevant decomposition reactions.Anexample of the results of this approach is shown in Fig 1 due to Halstead.The quantity of hydrogen formed is relativelyhigh and insensitive to temperature; formation of acetylene becomes appreciable only at temperatures nearing 100o c.Formation of methane, ethane, and ethylene each also have unique dependences on temperature in the model.Thethermodynamic approach has limits; it must assume an idealized but nonexistent isothermal equilibrium in the regionof a fault, and there is no provision for dealing with multiple faults in a transformer.However, the concentrations of theindividual gases actually found in a transformer can be used directly or in ratios to estimate the thermal history of theoil in the transformer from a model and to adduce any past or potential faults on the unit.As the simplest example: thepresence of acetylene suggests a high temperature fault, perhaps an arc, has occurred in the oil in a transformer, thepresence of methane suggests that—if a fault has occurred—it is a lower energy electrical or thermal fault.Much workhas been done to correlate predictions from thermodynamic models with actual behavior of transformers.IEEE C57.104 pdf download.