Improvement Of The Second Order Kinetic Model Based On Oil-Paper In- Sulation Thermal Aging Properties

Oil-immersed power transformers are the core of the power system, its operating status related to the safety of power grid. Safe and stable operation of power transformers depend on the merits of its insulating properties. Water and carboxylic acids exert a significant impact on the aging rate of oil-paper insulation system. Hydrolysis reaction between water and cellulose is the main form of cellulose aging. Glucosyl 1-4-β-glycosidic bond was broken during the hydrol-ysis reaction, meanwhile, the cellulose molecules degraded to short-chain molecules. Short-chain molecules further hydrolysis into low molecular weight carboxylic acid and water. The role of low molecular weight carboxylic acid can’t be ignored in terms of aging acceleration because the majority of low molecular weight carboxylic acid remain in insulating paper and synergy with water. Currently, there are a large number of domestic and international research about the effect of water and carboxylic acid on the aging characteristics of oil-paper insulation system. But the quantitative research which about the effect of carboxylic acid on aging rate of insulating paper is rare. Therefore, this paper will launch a quantitative research on the synergy between carboxylic acid and water based on the thermal aging characteristics of insulating paper.Currently, there are numerous mathematical model on aging characteristics of oil-paper insulation such as first-order kinetic model, second-order kinetic model and cumulative degra-dation kinetic model for loss of DP of cellulose. But the accuracy of the model uneven. Further-more, some problems exist in the existing models, for example, equivocal meaning of kinetic equation parameters and the impact factors of aging factors are distinguished unclearly. There-fore, thermal aging experiments will be designed and developed based on the former research on the thermal aging characteristics of insulating paper. Finally, the second-order kinetic model will be improved and refined based on these experiments.Currently, the application of the second-order kinetic model is still limited in laboratory, its engineering value is limited. The degree of polymerization (DP) of insulating paper that inside the transformer requires a direct measurement during the application process of existing sec-ond-order kinetic model. This can’t be achieved for the measurement requires the hanging hood coring operation to a transformer. In addition, a number of factors will influence the measure-ment error of DP, resulting in the expansion of measurement error. To avoid measurement error enlargement resulted from direct measurement of the DP of insulating paper, this paper attempts to establish the function between parameters (kto and k2) of the second-order kinetic model and the operating environment parameters (temperature, moisture and acidity) of insulating paper by experimental study. The establishment of the functional relationship between parameters will provide a new way to get the DP data of insulating paper. During the embodiment, the water content and acidity of insulating oil will be measured firstly, then the water content and acid content of insulating paper can be calculated via balanced distribution curves. Afterwards, the parameters of the second-order kinetic model can be calculated via the function that estab-lished in this paper. Then, we will get the second-order kinetic model whose parameters are known by substituting kto and k2 into the second order kinetic model. Finally, this model will be applied to assess the aging condition of insulating paper and predict its life. The establish-ment of the functional relationship between the model parameters and the runtime parameters of insulating paper laid the foundation for engineering application of second-order kinetic model.During the establishment of the function between parameters, the second-order kinetic model is applied to fitting the experimental data to obtain kto and k2, kto is defined as the initial aging rate of insulating paper, meanwhile, k2 is defined as the constant that weigh the operating environment of insulating paper. The values of kto and k2 were further fitted to establish the functional relationship to the parameters that initial moisture content (w) of paper and acid con-tent (v) of oil. Finally, the second-order kinetic model has been improved and refined.