Moisture and thermal aging effects on the FDS measurement of silicone oil-paper insulation

As an alternative insulating liquid of mineral oil, the silicone oil is widely used in the high voltage apparatuses where fireproofing and environment must be considered. Both the thermal aging and moisture threaten the reliability of the oil-paper insulating system. As a nondestructive measurement method, the frequency domain spectroscope (FDS) property of the electric apparatus has been used to assess the moisture content and aging condition of the mineral oil-paper composed insulating system. However, whether FDS is suitable for the assessment of silicone oil-paper composed insulating system is still unknown. To clarify how the thermal aging and moisture influence the FDS property of the silicone oil-paper is significantly meaningful. In this paper, the accelerated thermal aging experiments are performed on both silicone oil and mineral oil impregnated paper samples at high temperature. FDS measurements of samples with different aging time and moisture are performed then. Experiment results show that for the mineral oil-paper system, both the thermal aging and moisture impact the FDS results a lot in the low frequency region and it is very hard to separate them apart clearly. However, for the silicone oil-paper system, the moisture significantly impacts the FDS results while the thermal aging plays a slight role. Therefore, compared to the mineral oil-paper system electric apparatuses, the FDS method maybe much more suitable to estimate moisture content for the silicone oil-paper insulation apparatuses.