A significant proportion of power transformers installed across the world approaching the end of their designed life. One reason for a power transformer to reach the end of its life is that its paper insulation has degraded to the point where it has lost its tensile strength. The rate at which paper degrades is mainly related to the temperatures within the transformer and the water content of its solid insulation. Being able to monitor the water content of transformer solid insulation would be very desirable to improve the maintenance of the equipment. In a previous work, a sensor to monitor this variable was proposed by the authors. In this paper the characterization of Sensor's dielectric response is presented through a multiphysics model under inhomogeneous moisture distribution using Frequency Dielectric Spectroscopy (FDS) method.