Moisture detector in biodegradable esters

Abstract

The moisture content of insulating oils is one of the important parameters affecting the dielectric properties and reliability of the entire transformer. Water can be introduced into the insulating oil due to thermal oxidative aging of cellulose or ester itself, or from the surrounding atmosphere due to low pressure. One of the promising methods for quantifying the amount of water in insulating fluids is measuring of frequency dependence of dielectric properties of oil. It can be done through oil sensor onsite or in laboratory conditions studied using broadband dielectric spectroscopy method. We have studied a dielectric response of biodegradable oil samples in a defined electric field over a specified temperature interval as a function of frequency. A BDS 1308 two-electrode system was used to measure liquid samples. Three different types of insulating oils were compared during the measurement. The insulating oils were the mineral oil Nynas Lyra, the synthetic ester oil Midel 7131, and the natural insulating oil Envirotemp FR3. Samples were compared before and after the drying process. Drying was carried out for 46 hours at 60 °C. Subsequently, the water content in the samples was calibrated by Karl Fisher coulometric titration measurement. The test proceeds from - 60 °C to 60 °C in 10 °C intervals at a frequency range from 0.01 Hz to 1 MHZ. The results proved the impact of water content on the resulting dielectric properties as a function of frequency and are used in the model designed for online onsite measurement.