Abstract：Oil-paper insulation is of vital importance for power transformers; and their chemical and mechanical performance will vary with the operation. However, traditional methods of aging assessment are generally destructive or time-costing. To address these issues, this paper proposes an aging assessment method of oil-immersed insulating paperboard based on the electromechanical impedance. Reflecting the mechanical performance of the insulating paper, it can provide the novel evidence for aging classification of insulating paper. Firstly, a vibration model of the paper-piezoelectric material system is established considering the coupling effects of mechanical and electric fields. The electromechanical impedance expression of the paper-piezoelectric material system is derived based on the principle of stationary action. The electromechanical impedance equation of the system shows that the amplitude and equivalent angular frequency of the electromechanical impedance spectrum of the paper-piezoelectric material system are related to the coupled system stiffness and the equivalent mass. In addition, the complex modulus of elasticity characterizes the stiffness of the oil-paper system, achieving the simulation of electromechanical impedance characteristics under different aging states. Due to the long-time aging, the variation in complex modulus of elasticity, i.e., the difference in equivalent stiffness leads to the larger electromechanical impedance and smaller intrinsic frequency. Furthermore, the experiments demonstrate the electromechanical impedance characteristics of the insulting paper with the different aging duration, which are comparable to the simulation. The effect of the number of insulation paper layers is also taken into consideration, which is necessary to be normalized when extracting aging characteristic parameters. The normalized root-mean-square deviation of the electromechanical impedance is selected to assess the aging degree of oil-immersed insulating paperboard. Finally, the correspondence between the aging state of oil-paper, mechanical strength and electromechanical impedance characteristics is investigated. The following conclusions can be drawn from the simulation and experiment analysis: (1) The peak impedance of a paper-piezoelectric material system correlates positively with the degree to which the insulating paper has aged. The longer the aging time, the stiffer the system becomes, and the larger the impedance peak becomes. Additionally, the entire electromechanical impedance spectrum shifts to the left. As the number of insulating paper layers increases, the equivalent mass of the paper-piezoelectric material system rises, resulting in an increase in the peak magnitude of the main-frequency impedance spectrum and a shift of the peak frequency toward lower frequencies. Concurrently, the rate of increase in peak magnitude diminishes with additional layers. (2) The compression modulus of the insulating paper decreases with aging. This leads to a decrease in the equivalent stiffness of the paper-piezoelectric material system. In turn, this causes a significant increase in the normalized root-mean-square deviation of the resonance peaks of the electromechanical impedance spectrum. The aging assessment based on the normalized root-mean-square deviation is also suitable to the multi-layer insulating paper. (3) The aging state (degree of polymerization) and mechanical state (compression modulus) of the insulating paper correspond to the inverse of the root-mean-square deviation of electromechanical impedance (main frequency). The higher the aging degree of the insulating paper, the smaller the values of these parameters are. Hence, it offers a novel method for non-destructively evaluating the aging state of insulating paper.
黄秀君, 汲胜昌, 曹文博, 杨宇翔, 张凡. 基于压电阻抗技术的油浸绝缘纸板老化评估方法[J]. 电工技术学报, 2026, 41(11): 3882-3892.
Huang Xiujun, Ji Shengchang, Cao Wenbo, Yang Yuxiang, Zhang Fan. Aging Assessment of Oil-Immersed Insulating Paperboard Based on Electromechanical Impedance Technology. Transactions of China Electrotechnical Society, 2026, 41(11): 3882-3892.
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