Paper & power: modifying electrical insulation paper

Abstract

Paper is employed in conjunction with oil in the electrical industry to insulate high voltage cables and transformers. This research examines changes in the electrical performance of insulation paper as a result of changes to its structure and surface properties. In addition to the electrical properties of the base paper, the effects of fibre type, fillers and the role of paper additives were investigated. Variations in filler content, density, thickness, smoothness and porosity were also considered for their impact on the dielectric breakdown strength of oil-paper insulation.

Of the three fibre types that were tested, the industry standard unbleached kraft pulp performed best electrically. Of the two fillers that were tried, the hydrophobic talcum filler clearly outperformed the hydrophilic bentonite filler. In comparison to the unfilled samples, the latter severely degraded the electrical breakdown strength of the paper, whereas the talcum filled samples displayed improved electrical performance. The high amount of filler employed in the trials reduced the mechanical strength of the papers and lead to the trial of additives to address this effect. The addition of both cationic starch and polyvinyl alcohol (PVA) increased the mechanical strength of the paper and showed positive results in the electrical breakdown tests. The dielectric spectroscopy measurements, however, revealed a marked increase in permittivity and dielectric loss for the samples containing the cationic starch. The use of PVA appeared to alleviate this effect. In a similar vein, calendering as a surface treatment showed positive results for the electrical breakdown strength, but a negative influence on the dielectric performance.

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ORCID for P.L. Lewin: orcid.org/0000-0002-3299-2556

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