Evaluation of diffusion-driven material property profiles using three-wavelength interdigital sensor

The response of a three-wavelength interdigital dielectrometry sensor to the moisture diffusion process in oil-impregnated transformer pressboard has been simulated using an empirical relationship between the moisture concentration and the dielectric properties of the pressboard. A benchmark test of the moisture diffusion process has been developed with the purpose of comparing alternative parameter estimation algorithms used in ω-κ (frequency wavenumber) dielectrometry. The results of simulations highlight characteristic features of the multi-wavelength sensor response, such as the sensor response delay from the start of the transient moisture diffusion process as a function of sensor wavelength, the influence of moisture boundary conditions, and the relation between the signal magnitude and variations of dielectric properties. One of the parameter estimation algorithms, linear calibrated admittance-based estimation (LCABE), has been applied to both simulated and measured data. Adequate performance of the LCABE approach in the absence of strong discontinuities of dielectric properties in the electric field penetration region is demonstrated and contrasted to an electrically shielded region case, in which the signal response becomes nonlinear. The proposed approach offers significant potential for the measurement of diffusion processes in various dielectrics, especially for cases with highly irregular geometry or material structure. Measurement results from moisture diffusion process monitoring are included. Parameter estimation of measurement results with LCABE confirm its applicability to the monitoring of moisture dynamics in transformer pressboard