Aging Characterization of Oil-paper Insulation Based on Fluorescence Characteristics of Suspended Fibers in Oil

The aging assessment of paper insulation is important for the operation, maintenance, overhaul, and decommissioning of transformers. This paper presents a new method for assessing the aging of paper insulation in oil-immersed transformers based on the fluorescence characteristics of suspended fibers in oil. Accelerated thermal aging experiments are performed on oil-paper specimens at 120°C and 130°C to obtain fiber samples with different degrees of aging. Fluorescence emission(Em) and excitation(Ex) spectra of these fibers are obtained using a fluorescence characteristic test platform. The experimental results show that the fluorescence intensity decreases with the increase of aging and the fluorescence peak position is gradually red-shifted. The mechanism of the fluorescence characteristics of fibers before and after thermal aging is studied by molecular simulation. The results show that fiber fluorescence intensity decreases with hydrogen bond strength and number reduction during thermal aging. Finally, a new aging characteristic parameter-fluorescence lifetime based on transient fluorescence characteristics of fibers-is proposed. The relationship between it and the degree of polymerization is obtained. The fluorescence characteristics of fibers in oil show their potential for online monitoring of paper insulation aging.