A methodology for determining water saturation limits and moisture equilibrium diagrams of alternative insulation systems

In recent years one can observe a higher interest in alternative dielectric materials for power transformers. These are for example natural and synthetic esters or aramid fiber based solid insulation materials. In this paper moisture saturation curves of various insulation oils are presented up to a temperature of 140°C, together with the sorption isotherms of Nomex® pressboard. These lead to adjusted equilibrium charts for moisture diagnosis of transformers with unconventional insulation systems.