Diffusion coefficient in transformer pressboard insulation part 1: non impregnated pressboard

Abstract

Water is harmful for transformers; the dynamic behavior of moisture influences the dielectric integrity and insulation aging in a transformer on operation. In this paper, the determination of the diffusion coefficient of moisture in transformer pressboard is tackled. This work has been focused in analyzing non oil-impregnated pressboard, so the obtained coefficient is useful for studying the processes of transformer drying in factory. Drying experiments were developed in a thermogravimetric analyzer on nonimpregnated samples of pressboard subjected to different drying temperatures. The experimental conditions were simulated by means of a diffusion model implemented by means of Finite Element Method. The comparison between estimated and measured values allows drawing conclusions about the accuracy of the proposed coefficient.

Modified Expression of Moisture Diffusion Factor for Non-Oil-Immersed Insulation Paper

“…On the basis of reported studies in [20], Fig. 6 shows the extraction process of MDF based on diffusion model.…”

“…Based on the results reported by Guidi and Fullerton, Foss and Du conducted experiments to determine the parameter values of the empirical expression for different insulation materials [17]- [19]. Subsequently, Garcia optimized the expression of MDF by considering the effects of thickness [20]. Additionally, some scholars gave the experimental values of MDF for insulation paper in forms of curves and tables [21].…”

“…here D 1 and D 2 are constants when the sample has fixed thickness; k is constant and equals 0.43 for non-oil-immersed insulation paper [20]; and T is temperature, the unit of which is Kelvin. The above studies provide the basis for analysis of drying process, and they are helpful to optimize the drying process.…”