Thermodynamic Computation Method of Thermal Decomposition Gas Content in Transformer Oil Considering Temperature and Competitive Reaction

Dissolved gas analysis (DGA) is one of the most essential methods for troubleshooting oil-immersed transformers in the power industry. The demand for quantitative and digital DGA, particularly in computational high-voltage engineering applications, continuously increases. On the basis of thermodynamics principle, a computational method for determining the thermal decomposition gas content of alkane molecules in transformer oil was studied. In this approach, specific heat capacity serves as a temperature-dependent function, considering the effect of temperature on the chemical equilibrium constant. Moreover, the relationship between the enthalpy of the reaction and the equilibrium constant is derived, considering temperature. Competitive factors were proposed to quantify the number of moles of each substance in the reaction to characterize the phenomenon of varying extent of thermal decomposition reactions at a specific temperature, and the thermal decomposition equations of alkane molecules were established. This study used a mixed system of propane and butane for calculation. The computational validity of the proposed methodology was verified by analyzing and comparing the results with the gas generation in the transformer oil provided by the U.S. Department of the Interior, as well as by using the improved IEC ratios to output the types of faults associated with the gas generation.