Field-Dependent Dielectric Relaxation in Oil-Pressboard Insulation Systems

Inhalt:
Oil-pressboard barrier systems are operationally relevant insulation configurations that require intensive investigation regarding their dielectric response under direct current (DC) stress. In that regard, distinguishing between various relaxation phenomena is a step towards an enhanced understanding of the system. In this contribution, simultaneous electric field and current measurements were carried out on a specific configuration of oil and pressboard layers, and the results were analyzed with the aid of the numerical solution of Poisson-Nernst-Planck (PNP) equations. Measurements show that for the investigated electric field strength levels, the relaxation time of the system increases with the applied electric field strength, which is recognized from the shift of the electric field curves to longer times. Numerical results based on simple charge transport equations, widely applied within the context of electrical conduction in mineral oil, qualitatively confirmed this behavior. It is attempted to pinpoint a specific mechanism leading to this observation through parameter variation in the numerical calculations.