Parameter Identification Method of Hybrid Equivalent Circuit for Oil-Paper Insulation of Transformer Based on Spectral Decomposition Method
Lin Zhiyong1,2, Li Ronghua1,2, Deng Dongping3, Wu Yonghai4, Lin Renjie5
1. School of Electrical Engineering and Automation Xiamen University of Technology Xiamen 361024 China; 2. Xiamen Key Laboratory of Frontier Electric Power Equipment and Intelligent Control Xiamen 361024 China; 3. State Grid Fujian Electric Power Co. Ltd Zhangping Power Supply Company Zhangping 364400 China; 4. State Grid Fujian Electric Power Co. Ltd Longyan Power Supply Company Longyan 364000 China; 5. State Grid Fujian Electric Power Co. Ltd Jinjiang Power Supply Company Jinjiang 362200 China
Abstract：The extended Debye equivalent circuit model fails to accurately represent the aging characteristics of complex oil-paper insulation medium in transformers. Additionally, the identification method for the hybrid equivalent circuit, which relies on intelligent optimization algorithms, often produces non-unique and inaccurate results. Based on the functional relationship between the depolarization current and the hybrid equivalent circuit parameters, quadratic differential spectrum of depolarization current is constructed, and the characteristics of the sub spectra, as well as their internal relations to the corresponding polarization branch parameters, are analyzed. A method for identifying the parameters of the hybrid equivalent circuit is suggested. The specific idea and identification steps are as follows: (1) Beginning from the end of the quadratic differential time-domain spectrum of the depolarization current, the parameters of the series-type sub-spectrum at large time constants (t≥200 s) are resolved using the point- selection method. This step determines the polarization resistance and polarization capacitance of the corresponding branches with large time constants. (2) The parameters of the hybrid-type sub-spectrum at medium-time constants (2 s<t<200 s) are resolved using the point-selection method. This step determines the polarization resistance and polarization capacitance of the corresponding branches with medium time constants. (3) The parameters of the series-type sub-spectrum at small time constants (t≤2 s) are resolved using the point-selection method. The sub spectra are decomposed using the spectral decomposition method, and hybrid equivalent circuit parameters are further identified based on the parameters of the sub spectra. Finally, The traditional identification method and the spectral identification method are respectively applied to study the transformer T1 to verify the reliability of the method.The experiment results demonstrate that the traditional identification method has the following disadvantages: (1) Artificially assuming different numbers of polarization branches in advance will also affect the identification results of hybrid equivalent circuit parameters. (2) In the light of the complex relationship between the characteristics of the recovery voltage and the parameters of the hybrid equivalent circuit in the objective function of Equ.(10), different equivalent circuit parameters will also be obtained when the identification program is run each time under the condition of ensuring the identification accuracy. the quadratic differential time domain spectra of the depolarization current can effectively and accurately decompose the information related to the number of polarization branches, sub spectra parameters, and polarization branch parameters that are embedded within the depolarization current. The parameter identification process for the hybrid equivalent circuit, based on the spectrum decomposition method, is straightforward. The results of this identification are both accurate and unique, effectively reflecting the aging information of the depolarization current. It avoids the problems of randomness and multiple solutions in traditional parameter optimization processes. Furthermore, a comparative analysis is performed on multiple transformers in various aging states, utilizing the proposed method and the traditional method. The results indicate that the average fitting degree achieved by the proposed method is 0.97, which is on average 0.10 higher than that of the traditional method. This further substantiates that the quadratic differential spectral decomposition method can reliably and accurately identify the hybrid equivalent circuit parameters.
林智勇, 李荣华, 邓东平, 吴勇海, 林仁杰. 基于解谱法的变压器油纸绝缘混联等效电路参数辨识方法[J]. 电工技术学报, 2025, 40(19): 6283-6292.
Lin Zhiyong, Li Ronghua, Deng Dongping, Wu Yonghai, Lin Renjie. Parameter Identification Method of Hybrid Equivalent Circuit for Oil-Paper Insulation of Transformer Based on Spectral Decomposition Method. Transactions of China Electrotechnical Society, 2025, 40(19): 6283-6292.
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2025, Vol. 40 
