Abstract
An accelerated thermal aging process was used to simulate the condition of paper insulation in transformer oil-paper systems. Optical parameters of the insulation paper after various aging intervals were analyzed with terahertz time-domain spectroscopy (THz-TDS) over the range 0.1~1.8 THz. The result shows that the paper had seven absorption peaks at 0.19, 0.49, 0.82, 1.19, 1.43, 1.53, and 1.74 THz, and density functional theory of B3LYP/6-311G+ (d, p) was used to simulate the molecular dynamics of the repeating component (cellobiose) of the cellulose paper. Theoretical spectra were consistent with experiment, which had absorption peaks at 0.18, 0.82, 1.47, and 1.53 THz in the same frequency range. At the same time, the paper samples after various aging intervals had different refractive indexes, and least squares fitting revealed a linear relationship between the degree of polymerization and the refractive index of the paper. Hence, this paper demonstrates that THz-TDS could be used to analyze the aging condition of transformer insulation paper and provides the theoretical and experimental basis for detection.
Highlights
Terahertz (THz) radiation has wavelengths of 30 μm~3 mm (0.1~10 THz) between far-infrared and microwaves
The insulation paper was dried for 24 h at 343 K in a 500 Pa vacuum to keep the remaining water content less than 0.5%
Degassed insulating oil was heated to 313 K and injected into the container holding the insulation paper to produce an oil-paper ratio of 20:1
Summary
Terahertz (THz) radiation has wavelengths of 30 μm~3 mm (0.1~10 THz) between far-infrared and microwaves. It is a transitional region between macro-electronics and micro-photonics [1,2]. As a cutting-edge analytical technique, terahertz (THz) spectroscopy has multivariate characteristics, such as fingerprint absorption, coherence, and low ionization damage [3,4]. It is quite sensitive to different chemical composition and intermolecular interactions and oscillations of materials, and there are different fingerprint characteristics in the THz region [5,6]. Applications include security [11] and nondestructive testing [12]. THz technology has a great scientific research and application potential, with continuous development of THz emitters [13] and detectors [14]
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