Study on Diagnosis for Transformers by Tan $\delta$ and Moisture of Insulation Oil According to Thermal Aging

절연유의 열열화에 따른 Tan $\delta$와 수분의 변화에 의한 변압기의 예방진단 연구

This paper reports the experiments regarding to diagnosis techniques for power transformers by measuring dissipation factor and moisture contents of mineral oils. Thermal aging environments of mineral oils were varied by the specially designed systems. Thermal aging of elevated temperature of $90^{\circ}C$ was performed for about 240 and 460 hours, respectively. Dissipation factor, permittivity, and water content were measured. Our test samples were not exposed to air. Dissipation factor increased while permittivity did not change. The level of dissipation factor determining the insulating quality of mineral oil was compared with the previous results of resistivity and several correction factor.