Measurements and Modeling of Moisture in Transformer Insulation

The presence of moisture in a transformer deteriorates the insulation by decreasing its electrical, mechanical, and thermal strength. Therefore, it is critical to monitor the moisture condition in both liquid and solid insulation. This book performs an extensive study of on-line moisture monitoring for transformer insulation systems and provides new tools and advanced approaches on this topic. A new set of moisture equilibrium curves for oil and paper systems is constructed with a wider range than reported in prior literature. Such curves can be used to predict moisture in the paper insulation from oil moisture measurements taken when the system is in equilibrium. When the system is not in equilibrium, the three- wavelength interdigital dielectrometry sensor developed at MIT provides a unique way to non- destructively measure the spatial profile of the moisture distribution in transformer pressboard. A universal curve is found relating dielectric properties to moisture concentration and temperature. The diffusion coefficient for pressboard as a function of temperature and moisture concentration is estimated.