Polarization and Depolarization Current of Pressboard Impregnated with Natural Ester under Thermal Stress

Abstract

Mineral oil has long been utilized in transformers due to its low cost and suitable qualities. Alternative liquid insulations with great characteristics have recently been presented, and natural ester was considered. Pressboard is a type of cellulose insulation used for electrical insulation and mechanical support. This paper intends to study pressboard impregnated with natural ester under thermal stress. The pressboards and the natural ester were prepared for the experiment. Vacuum ovens were used for moisture elimination of materials and the impregnation process. The test specimens consisted of impregnated pressboards for 0, 8, 16, and 24 hours with thermal stress by heating at 150 degrees Celsius in a vacuum oven for 0, 30, and 90 days. Polarization and depolarization current (PDC) of the test specimens were investigated in each period by PDC-Analyser 1MOD. The test cell for PDC measurement was designed according to JIS C2111, and it was clean before the experiment. The PDC characteristics of the pressboard that had been subjected to thermal stress were discovered to be slightly different when compared with the same impregnation time of the pressboard.