Estimation of Moisture Content of Oil-Paper Insulation in Transformers Using Electric Modulus

Abstract

In this work, a novel technique has been proposed to estimate the moisture content of oil-paper insulation in transformers employing the concept and idea of electric modulus. Polarization and other relaxation mechanisms of dipoles in any dielectric are directly reflected in the electric modulus. Thus, electric modulus can be regarded as an important parameter to analyze the moisture and ageing condition in dielectrics. Considering the aforesaid fact, electric modulus has been used to estimate the moisture content of oil-paper insulation in transformers with reasonable accuracy. Samples of different moisture contents (1%, 2%, 3% and 4% by weight) were prepared in the laboratory and were subjected to sinusoidal excitation of frequency varying from 0.1 mHz-10 kHz to evaluate the frequency domain spectroscopy (FDS) characteristics of the sample. Using the FDS characteristics, the real and imaginary parts of the complex electric modulus were calculated. Two moisture sensitive characteristic parameters were extracted based on the variation of electric modulus with frequency. Later, it has been shown that using these two parameters the moisture content of the sample can be assessed with reasonable accuracy. This proposed technique can be used to assess the health conditions of oil-paper insulation in real life transformers also.