Abstract
The corrosive sulfur compounds present in the mineral oil causes the formation of dibenzyl disulfide (DBDS) complex and it can also erode the on-load tap changing selector contacts leading to generation of silver sulfide (AgS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ).The present work reports the effect of DBDS and Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S concentrations in mineral oil on thermally aged pressboard material. The results demonstrate that surface discharge inception voltage (SDIV) is higher for the aged pressboard specimen. The higher concentrations of DBDS showed a reduction of more than 50% in the magnitude of SDIV compared to its effect with the addition of Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S. The surface potential analysis indicates a higher initial potential for the aged specimens with an increased half lifetime. In addition, only deep traps observed on the aged specimens with a slight right shift in its trap energy level. The mechanical strength of aged pressboard specimens with DBDS and Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S is understood using tensile testing and simultaneous analysis is captured using Digital Image Correlation (DIC) technique to understand its strain percentage at different areas on the pressboard material during its elongation. The laser induced breakdown spectroscopy (LIBS) analysis is performed to identify the elements responsible for thermal ageing such as carbon, copper and sulfur on the surface of pressboard material. The plasma temperature calculated from sulfur peaks is higher for DBDS aged specimen compared to AgS <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> and a linear correlation is observed on the LIBS intensity with ageing duration. Further, the Principal Component Analysis (PCA) is used for its classification on the degradation of pressboard due to the diffusion of both copper and silver sulfide from the mineral oil. The two principal components (PC1 and PC2) provided a higher variance of 99.8% with a clear classification observed between the unaged and aged pressboard specimens due to the addition of both DBDS and Ag <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> S in mineral oil.
Highlights
The power system components, such as transformers and cables, employ liquid dielectrics as an insulating medium and coolant, and as an arc quencher in high voltage circuit breakers [1]
The present work considers the effect of dibenzyl disulfide (DBDS) and Ag2S diffusion towards the pressboard material through various surface characterization analysis with novel digital image correlation (DIC) technique adopted for its tensile strength and multivariate analysis of laser induced breakdown spectroscopy (LIBS) spectra coupled with principal component analysis (PCA) for its classification on the aged pressboard specimens
SURFACE DISCHARGE INCEPTION VOLTAGE The surface discharge inception voltage (SDIV) was measured based on the first discharge detected by the fluorescent fiber
Summary
The power system components, such as transformers and cables, employ liquid dielectrics as an insulating medium and coolant, and as an arc quencher in high voltage circuit breakers [1]. The present work considers the effect of DBDS and Ag2S diffusion towards the pressboard material through various surface characterization analysis with novel digital image correlation (DIC) technique adopted for its tensile strength and multivariate analysis of LIBS spectra coupled with PCA for its classification on the aged pressboard specimens.
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