Simulation of Long-Term Transformer Operation with a Dynamic Thermal, Moisture and Aging Model

This paper introduces a dynamic thermo-hydraulic network model for transformer applications. The model includes the dynamic performance of temperatures, moisture levels, oil flows and the temperature dependent losses, separated in individual windings and individual positions. Therefore, interactions between single windings and also the core are covered by this model which is not the case in standard models. The temperature and moisture values are applied to calculate the insulation aging at different positions. In IEC 60076-7 (2018) the influence of moisture and oxygen can be considered roughly for aging calculations while the determination of the local moisture levels is not part of the standard. Here this paper gives assistance to determine such local moisture levels during the life time of a transformer. The thermo-hydraulic model includes also the dynamic properties of moisture transport in solid and liquid insulation to determine the local moisture levels and DP-values in the insulation. Simulations point out the difference between the aging model of IEC and the model developed by the transformer manufacturer. In addition, the moisture generation during cellulose aging and the change of moisture absorption capability by aging are parts of the simulation studies in the paper.