Discrete Elements Thermo-Chemical Digital Twin Incorporating Oil and Paper Degradation

Understanding the distribution of the water inside a transformer is of paramount importance for assessing its degradation and reliability. The challenge lies in the lack of direct measurement solutions. Even systems hermetically sealed experience a gradual increase in the total water content. The degradation of the cellulose-based materials generates water as a byproduct, which accumulates inside the transformer gradually. The authors presented an article introducing the thermo-chemical model at this same conference in 2023 [1]. Based on the well-known initial conditions of the transformer, the water content of the insulating liquid and the solid insulation is recalculated for each numerical integration step iteratively, finding a new solution for the system of equations that distributes the total mass of water inside the transformer. The estimation of the solid insulation degradation rate takes into consideration the equations from Annex A of IEC 60076-7:2018 allowing a comparison with the traditional Arrhenius model. Paper degradation is used to calculate the stoichiometric generation of water due to the scissions of the cellulose molecules.The variation of the water saturation limit with the aging of mineral oil was incorporated into the model, as suggested during last year’s presentation. This calculation is based on the CIGRE Technical Brochure 741 [2], and the IEC 60422 [3].This paper presents the resultant model and the results of the simulation of the life of transformers submitted to different loading conditions. The method was named "Thermo-Chemical Digital Twin". It applies a variation of Runge–Kutta methods for integrating the life consumption of the transformer based on successive steps of loading application, dynamically representing several thermo-chemical processes. The iterative calculation stops when the accumulated life consumption reaches 180,000 hours.