A study of the temperature-based dynamic nature of characteristic gases in oil-cellulose insulation systems

Dissolved Gas Analysis (DGA) is a well established method to monitor and predict the condition of devices with oil-cellulose insulation, especially power transformers. However, the effect of the migration of theses gases between the liquid and solid insulation is often ignored. The migration phenomenon is temperature dependent and, if ignored, can potentially lead to erroneous condition assessment by the DGA method. This paper addresses the dynamic nature of propagation of these gases in such systems based on temperature variations. Diffusion times, and therefore diffusivity of the gases, in oil-impregnated cellulose are calculated by identifying the diffusion process as a linear system. The diffusion time-constants, and steady-state condition at the working concentrations, are estimated based on the identified model. A sensitivity study is performed to show the dependency of the diffusion time-constants to the temperature and the oil-cellulose ratio in the system. The equilibrium curves are obtained in the case of carbon dioxide by using solubility information of this gas in the oil and paper pulp, similar to the case of moisture equilibrium. The results are compared with the experimental data. An example of the implication of the obtained data is shown.