Experimental validation of a moisture sensor for cellulosic insulation of power transformers

Abstract

Power transformers comprise one of the most important assets in the power systems. Damage in a power transformer can lead to a collapse in the electrical transmission network, disturbing a big number of users. The cellulosic insulation plays a key role in the life of power transformer. Several studies have demonstrated that high levels of moisture in the cellulosic insulation increase its rate of ageing limiting the power transformer's life expectancy. In this work, the experimental validation of a sensor aimed at determining the moisture content of cellulosic insulation is presented. The working principle of the sensor is based in the use of the Frequency Dielectric Spectroscopy method (FDS) to relate the main dielectric characteristics of the sensor and those of the transformer solid insulation. The validation presented in this work considers different temperatures and moisture contents under equilibrium and non-equilibrium conditions. Additionally, the experimental dielectric curves of the sensor are compared with simulation data obtained by means of a finite-element model that reproduces the applied experimental conditions, to validate the modeling process.