Abstract
Knowledge about moisture content in impregnated cellulose insulation is essential for power transformers when estimating remaining lifetime, planning operating conditions and drying procedure. Frequency dielectric spectroscopy (FDS) is non-destructive, convenient method to asses moisture content of insulation. It is important to study dielectric response of ester-cellulose insulation due to growing number of transformers using synthetic ester MIDEL 7131 as insulation fluid [1, 2]. The paper presents study of dielectric response of synthetic ester-pressboard samples with various moisture content (from dry to 5%) measured in wide temperature range (from 5 ˚C to 50 ˚C). Measurement results for pressboard impregnated with synthetic ester are compared to data of pressboard impregnated with mineral oil. The aim of presented work is to provide patterns of dielectric response of synthetic esterpressboard for accurate moisture content evaluation.
Highlights
Knowledge about moisture content in impregnated cellulose insulation is essential for power transformers when estimating remaining lifetime, planning operating conditions and drying procedure
Insulation system of typical power transformer consists of oil and impregnated cellulose in the form of pressboard and paper
The evaluation of water content using Frequency dielectric spectroscopy (FDS) is based on dielectric response patterns of impregnated pressboard for various moisture content, which contains characteristics of mineral oil impregnated pressboard
Summary
Knowledge about moisture content in impregnated cellulose insulation is essential for power transformers when estimating remaining lifetime, planning operating conditions and drying procedure. The evaluation of water content using FDS is based on dielectric response patterns of impregnated pressboard for various moisture content, which contains characteristics of mineral oil impregnated pressboard. Dielectric liquids like MIDEL 7131 – the synthetic ester, are used as an alternative instead of mineral oil. It was observed that type of impregnating liquid has influence on dielectric response of pressboard [3,4].
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