Abstract
Oil-impregnated insulation paper is an important part of transformers; its performance seriously affects the life of power equipment. It is of significance to study the aging characteristics and mechanism of oil-impregnated insulation paper under thermal stress for transformer status detection and evaluation. In the work, the accelerated thermal aging was carried out at 120 °C, and DP1490, DP787, and DP311 samples were selected to represent the new, mid-aging, and late-aging status of the transformer, respectively. The space charge distribution within the specimens was measured by the pulsed electro-acoustic (PEA) method and the trap parameters were extracted based on the measurement curves. Further, the aging mechanism was studied by molecular simulation technology. A typical molecular chain defect model was constructed to study the motion of cellulose molecules under thermal stress. The experimental results show that the corresponding trap energy levels are 0.54 eV, 0.73 eV, and 0.92 eV for the new specimen, the mid-aging specimen, and the late aging specimen, respectively. The simulation results show that the trapped energy at the beginning of aging is mainly determined by the loss of H atoms. The changes in trap energy in the middle stage of aging are mainly caused by the absence of some C atoms, and the trap energy level at the end of aging is mainly caused by the breakage of chemical bonds. This study is of great significance to reveal the aging mechanism of oil-impregnated insulation paper and the modification of insulation paper.
Highlights
The trap parameters of oil-paper insulation under thermal aging were studied based on the experiment and molecular simulation
The trap energy level at the non-aging stage is about 0.54 eV, which indicates that the cellulose is intact at this stage and a small amount of H atom deletion exists
The trap characteristic parameters are extracted through space charge curves, and the trap change mechanisms are explained by molecular simulation
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The power transformer is the key component of the high-voltage DC (HVDC) transmission project. The oil-impregnated paper, as the main insulation of the power transformer, plays an important role in the safe operation of electrical equipment. During the operation of the transformer, the insulation paper is prone to generating space charge due to the influence of thermal stress and other factors, which will cause local electric field distortion, aging, and breakdown of the insulation system, and poses a great threat to the safe and reliable operation of equipment [1,2,3,4,5]
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