The Polarization and Depolarization Current Characteristics of Mineral Oil, Natural Ester (FR3), Palm Oil, and Liquid Impregnated Pressboard

Abstract

Polarization and Depolarization Current (PDC) measurement is a non-destructive dielectric testing method used to determine the electrical properties of transformer insulation. Nowadays, natural ester has been used as alternative liquid insulation in transformers because it can be easily decomposed, highly flammable, resistant to moisture, and prolong of pressboard (solid insulation in a transformer) compared with mineral oil. Furthermore, palm oil is also an interestingly alternative insulating liquid. This paper presents the PDC characteristics of mineral oil, natural ester (FR3), and palm oil under various temperatures. All received liquid specimen were dry in the controlled temperature oven at 70°C under 200 mbar and then they were cooled down to ambient temperature around 25-30°C. The liquid samples were investigated for three cases as follows: 1) moisture content measurement according to ASTM D1533, 2) dielectric dissipation factor measurement as per ASTM D924, and 3) polarization current and depolarization current measurement at liquid temperature of 30°C, 50°C, and 70°C respectively. The PDC characteristics of mineral oil impregnated pressboards and natural ester impregnated pressboards were also investigated. The PDC test results were analyzed. It was found that the dielectric response of mineral oil was significantly different from natural ester (FR3) and palm oil. Besides, it was clearly that the conduction current of liquid insulation increased with increasing liquid temperature. Moreover, the pressboard impregnated with natural ester provided better insulation characteristics such as lower conduction current than that of the pressboard impregnated with mineral oil.